{"id":516,"date":"2021-12-17T21:47:14","date_gmt":"2021-12-17T21:47:14","guid":{"rendered":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/7-geologic-time\/"},"modified":"2022-05-18T14:11:27","modified_gmt":"2022-05-18T14:11:27","slug":"7-geologic-time","status":"publish","type":"chapter","link":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/7-geologic-time\/","title":{"raw":"7 Geologic Time","rendered":"7 Geologic Time"},"content":{"raw":"[caption id=\"attachment_3216\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Grand_Canyon_Beauty-scaled.jpg\"><img class=\"size-large wp-image-3216\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2021\/12\/Grand_Canyon_Beauty-scaled-1.jpg\" alt=\"The canyon is shown with many layers\" width=\"1024\" height=\"683\"><\/a> Perhaps no place on Earth better exemplifies the principles geologists use to determine the ages of rocks than Arizona\u2019s Grand Canyon National Park.[\/caption]\n\n<b>KEY CONCEPTS<\/b>\n<ul>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Explain the difference between relative time and numeric time<\/span><\/li>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Describe the five principles of [pb_glossary id=\"1937\"]stratigraphy[\/pb_glossary]<\/span><\/li>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Apply [pb_glossary id=\"2031\"]relative dating[\/pb_glossary] principles to a block diagram and interpret the sequence of geologic events<\/span><\/li>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Define an [pb_glossary id=\"1779\"]isotope[\/pb_glossary], and explain [pb_glossary id=\"2046\"]alpha decay[\/pb_glossary], [pb_glossary id=\"1223\"]beta decay[\/pb_glossary], and [pb_glossary id=\"1225\"]electron capture[\/pb_glossary] as mechanisms of [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] decay<\/span><\/li>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Describe how radioisotopic dating is accomplished and list the four key [pb_glossary id=\"1779\"]isotopes[\/pb_glossary]\u00a0used<\/span><\/li>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Explain how carbon-14 forms in the [pb_glossary id=\"1745\"]atmosphere[\/pb_glossary] and how it is used in dating recent events<\/span><\/li>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Explain how scientists know the numeric age of <\/span><span style=\"font-weight: 400\">the Earth and other events in Earth history<\/span><\/li>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Explain how sedimentary sequences can be dated using radioisotopes and other techniques<\/span><\/li>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Define a [pb_glossary id=\"1228\"]fossil[\/pb_glossary] and describe types of [pb_glossary id=\"1228\"]fossils[\/pb_glossary] preservation<\/span><\/li>\n \t<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Outline how natural selection takes place as a mechanism of evolution<\/span><\/li>\n \t<li style=\"font-weight: 400\">Describe [pb_glossary id=\"1237\"]stratigraphic correlation[\/pb_glossary]<\/li>\n \t<li style=\"font-weight: 400\">List the [pb_glossary id=\"1242\"]eons[\/pb_glossary], [pb_glossary id=\"1243\"]eras[\/pb_glossary], and [pb_glossary id=\"1244\"]periods[\/pb_glossary] of the geologic time scale and explain the purpose behind the divisions<\/li>\n \t<li>Explain the relationship between time units and corresponding rock units\u2014[pb_glossary id=\"1239\"]chronostratigraphy[\/pb_glossary] versus [pb_glossary id=\"1238\"]lithostratigraphy[\/pb_glossary]<\/li>\n<\/ul>\n[caption id=\"attachment_3217\" align=\"alignright\" width=\"225\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Portrait_of_Nicolas_Stenonus.jpg\"><img class=\"wp-image-464 size-full\" title=\"Unsigned but attributed to court painter Justus Sustermans\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Portrait_of_Nicolas_Stenonus.jpg\" alt=\"It shows a man\" width=\"225\" height=\"300\"><\/a> Nicolas Steno, c. 1670[\/caption]\n\n<span style=\"font-weight: 400\">The geologic time scale and basic outline of Earth\u2019s history were worked out long before we had any scientific means of assigning numerical age units, like years, to events of Earth history. Working out Earth\u2019s history depended on realizing some key principles of relative time. Nicolas Steno (1638-1686) introduced basic principles of [pb_glossary id=\"1937\"]stratigraphy[\/pb_glossary], the study of layered rocks, in 1669<\/span><span style=\"font-weight: 400\">. William Smith (1769-1839), working with the [pb_glossary id=\"1935\"]strata[\/pb_glossary] of English [pb_glossary id=\"1934\"]coal[\/pb_glossary] [pb_glossary id=\"2402\"]mines[\/pb_glossary], noticed that [pb_glossary id=\"1935\"]strata[\/pb_glossary] and their sequence were consistent throughout the region. Eventually he produced the first national geologic map of Britain<\/span><span style=\"font-weight: 400\">,<\/span><span style=\"font-weight: 400\"> becoming known as \u201cthe Father of English Geology.\u201d Nineteenth-century scientists developed a relative time scale using Steno\u2019s principles, with names derived from the characteristics of the rocks in those areas. The figure of this geologic time scale shows the names of the units and subunits. Using this time scale, geologists can place all events of Earth history in order without ever knowing their numerical ages. The specific events within Earth history are discussed in <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/8-earth-history\/\">Chapter 8<\/a>. \u00a0<\/span>\n<h2><span style=\"font-weight: 400\">7.1 Relative Dating<\/span><\/h2>\n[caption id=\"attachment_3218\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.1_Geologic_time_scale.gif\"><img class=\"wp-image-465 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.1_Geologic_time_scale-300x300.gif\" alt=\"Chart showing the names of the unit of the Geooogic Time Scale\" width=\"300\" height=\"300\"><\/a> Geoloigic Time Scale[\/caption]\n\n&nbsp;\n\n<span style=\"font-weight: 400\"><strong>[pb_glossary id=\"2031\"]Relative dating[\/pb_glossary]<\/strong> is the process of determining if one rock or geologic event is older or younger than another, without knowing their specific ages\u2014i.e., how many years ago the object was formed. The principles of relative time are simple, even obvious now, but were not generally accepted by scholars until the scientific revolution of the 17th and 18th centuries<\/span><span style=\"font-weight: 400\">. James Hutton (see <a href=\"http:\/\/opengeology.org\/textbook\/1-understanding-science\/#14_Foundations_of_Modern_Geology\">Chapter 1<\/a>) realized geologic processes are slow and his ideas on [pb_glossary id=\"1736\"]uniformitarianism[\/pb_glossary] (i.e., \u201cthe present is the key to the past\u201d) provided a basis for interpreting rocks of the Earth using scientific principles.<\/span>\n<h3><\/h3>\n<h3><\/h3>\n<h3>7.1.1 Relative Dating Principles<\/h3>\n<b>[pb_glossary id=\"1937\"]Stratigraphy[\/pb_glossary] <\/b>is the study of layered sedimentary rocks. This section discusses principles of relative time used in all of geology, but are especially useful in [pb_glossary id=\"1937\"]stratigraphy[\/pb_glossary].\n\n[caption id=\"attachment_3219\" align=\"alignright\" width=\"228\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.2_IsfjordenSuperposition.jpg\"><img class=\"wp-image-466 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition-228x300.jpg\" alt=\"Photo of superposed strata with the younger on top of the older\" width=\"228\" height=\"300\"><\/a> Lower strata are older than those lying on top of them.[\/caption]\n\n&nbsp;\n\n<b><b>[pb_glossary id=\"2032\"]Principle of Superposition[\/pb_glossary]: <\/b><\/b>In an otherwise undisturbed sequence of sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary], or rock layers, the layers on the bottom are the oldest and layers above them are younger.\n\n<b><b>[pb_glossary id=\"2033\"]Principle of Original Horizontality[\/pb_glossary]: <\/b><\/b>Layers of rocks deposited from above, such as [pb_glossary id=\"1756\"]sediments[\/pb_glossary] and [pb_glossary id=\"1751\"]lava[\/pb_glossary] flows, are originally laid down horizontally. The exception to this principle is at the margins of basins, where the [pb_glossary id=\"1935\"]strata[\/pb_glossary] can slope slightly downward into the [pb_glossary id=\"508\"]basin[\/pb_glossary].\n\n[caption id=\"attachment_3220\" align=\"aligncenter\" width=\"420\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995.jpg\"><img class=\"wp-image-467\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995-300x105.jpg\" alt=\"Photo of Grand Canyon strata showing that they are continuous across the canyon\" width=\"420\" height=\"147\"><\/a> Lateral continuity[\/caption]\n\n<b>[pb_glossary id=\"2034\"]Principle of Lateral Continuity[\/pb_glossary]: <\/b>Within the depositional [pb_glossary id=\"508\"]basin[\/pb_glossary], [pb_glossary id=\"1935\"]strata[\/pb_glossary] are continuous in all directions until they thin out at the edge of that [pb_glossary id=\"508\"]basin[\/pb_glossary]. Of course, all [pb_glossary id=\"1935\"]strata[\/pb_glossary] eventually end, either by hitting a geographic barrier, such as a ridge, or when the depositional process extends too far from its source, either a [pb_glossary id=\"1756\"]sediment[\/pb_glossary] source or a [pb_glossary id=\"228\"]volcano[\/pb_glossary]. [pb_glossary id=\"1935\"]Strata[\/pb_glossary] that are cut by a canyon later remain continuous on either side of the canyon.\n\n[caption id=\"attachment_3221\" align=\"alignleft\" width=\"225\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.6_Multiple_Igneous_Intrusion_Phases_Kosterhavet_Sweden.jpg\"><img class=\"wp-image-468 size-medium\" title=\"By Thomas Eliasson of Geological Survey of Sweden http:\/\/www.flickr.com\/people\/geologicalsurveyofsweden\/ [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by\/2.0&quot;>CC BY 2.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AMultiple_Igneous_Intrusion_Phases_Kosterhavet_Sweden.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.6_Multiple_Igneous_Intrusion_Phases_Kosterhavet_Sweden-225x300.jpg\" alt=\"Photo of rock outcrop with a dike cutting through an older rock and another dike cutting across that one.\" width=\"225\" height=\"300\"><\/a> Dark dike cutting across older rocks, the lighter of which is younger than the grey rock.[\/caption]<b>[pb_glossary id=\"2035\"]Principle of Cross-Cutting Relationships[\/pb_glossary]:<\/b><span style=\"font-weight: 400\">\u00a0 [pb_glossary id=\"495\"]Deformation[\/pb_glossary] events like [pb_glossary id=\"502\"]folds[\/pb_glossary], [pb_glossary id=\"2143\"]faults[\/pb_glossary] and [pb_glossary id=\"1753\"]igneous[\/pb_glossary] intrusions that cut across rocks are younger than the\u00a0<\/span><span style=\"font-weight: 400\">rocks they cut across<\/span><span style=\"font-weight: 400\"><span style=\"font-weight: 400\"><span style=\"font-weight: 400\">.\u00a0<\/span><\/span><\/span>\n\n<strong>Principle of I<\/strong><b>nclusions: <\/b><span style=\"font-weight: 400\">When one rock [pb_glossary id=\"2038\"]formation[\/pb_glossary] contains pieces or [pb_glossary id=\"2036\"]inclusions[\/pb_glossary] of another rock, the included rock is older than the [pb_glossary id=\"1935\"]host rock[\/pb_glossary].<\/span>\n\n[caption id=\"attachment_3222\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.7_Faunal_sucession.jpg\" target=\"_blank\" rel=\"noopener noreferrer\"><img class=\"wp-image-469 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.7_Faunal_sucession-300x220.jpg\" alt=\"Diagram showing layers containing fossils. Lines correlating the strata with equivalent fossil content.\" width=\"300\" height=\"220\"><\/a> Fossil succession showing correlation among strata.[\/caption]\n\n<strong><b>Principle<\/b> of [pb_glossary id=\"1228\"]Fossil[\/pb_glossary] Succession:<\/strong>Evolution has produced a succession of unique [pb_glossary id=\"1228\"]fossils[\/pb_glossary] that correlate to the units of the geologic time scale. Assemblages of [pb_glossary id=\"1228\"]fossils[\/pb_glossary] contained in [pb_glossary id=\"1935\"]strata[\/pb_glossary] are unique to the time they lived, and can be used to correlate rocks of the same age across a wide geographic distribution. Assemblages of [pb_glossary id=\"1228\"]fossils[\/pb_glossary] refers to groups of several unique [pb_glossary id=\"1228\"]fossils[\/pb_glossary] occurring together.\n<h3><b>7.1.2 Grand Canyon Example<\/b><\/h3>\n[caption id=\"attachment_3223\" align=\"alignright\" width=\"392\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.8_Grand_canyon_march_2013.jpg\"><img class=\"wp-image-470\" title=\"\u00a9 Tomas Castelazo, <a rel=&quot;nofollow&quot; class=&quot;external text&quot; href=&quot;http:\/\/www.tomascastelazo.com&quot;>www.tomascastelazo.com<\/a>&amp;nbsp;\/&amp;nbsp;<a href=&quot;\/wiki\/Main_Page&quot; title=&quot;Main Page&quot;>Wikimedia Commons<\/a>, <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AGrand_canyon_march_2013.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.8_Grand_canyon_march_2013-300x200.jpg\" alt=\"Photo of the Grand Canyon showing expanse of canyon and the various rock layers\" width=\"392\" height=\"262\"><\/a> The Grand Canyon of Arizona[\/caption]\n\nThe Grand Canyon of Arizona illustrates the [pb_glossary id=\"1937\"]stratigraphic[\/pb_glossary] principles. The photo shows layers of rock on top of one another in order, from the oldest at the bottom to the youngest at the top, based on the [pb_glossary id=\"2032\"]principle of superposition[\/pb_glossary]. The predominant white layer just below the canyon rim is the Coconino [pb_glossary id=\"1912\"]Sandstone[\/pb_glossary]. This layer is laterally continuous, even though the intervening canyon separates its outcrops. The rock layers exhibit the [pb_glossary id=\"2034\"]principle of lateral continuity[\/pb_glossary], as they are found on both sides of the Grand Canyon which has been carved by the Colorado [pb_glossary id=\"2212\"]River[\/pb_glossary].\n\n&nbsp;\n\n[caption id=\"attachment_3224\" align=\"alignright\" width=\"450\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.3_Stratigraphy_of_the_Grand_Canyon.png\"><img class=\"wp-image-471\" title=\"Image in the public domain.\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.3_Stratigraphy_of_the_Grand_Canyon.png\" alt=\"Diagram showing the three classes of rocks in the Grand Canyon: the oldest metamorphic and granitic rocks of the inner gorge, the tilted and block faulted strata of the later Precambrian Grand Canyon Supergroup, and the horizontal Paleozoic strata of the canyon walls.\" width=\"450\" height=\"614\"><\/a> The rocks of the Grand Canyon[\/caption]\n\nThe diagram called \u201cGrand Canyon\u2019s Three Sets of Rocks\u201d shows a cross-section of the rocks exposed on the walls of the Grand Canyon, illustrating the [pb_glossary id=\"2035\"]principle of cross-cutting relationships[\/pb_glossary], [pb_glossary id=\"2032\"]superposition[\/pb_glossary], and [pb_glossary id=\"2033\"]original horizontality[\/pb_glossary]. In the lowest parts of the Grand Canyon are the oldest sedimentary [pb_glossary id=\"2038\"]formations[\/pb_glossary], with [pb_glossary id=\"1753\"]igneous[\/pb_glossary] and [pb_glossary id=\"1992\"]metamorphic[\/pb_glossary] rocks at the bottom. The [pb_glossary id=\"2035\"]principle of cross-cutting relationships[\/pb_glossary] shows the sequence of these events. The [pb_glossary id=\"1992\"]metamorphic[\/pb_glossary] [pb_glossary id=\"2007\"]schist[\/pb_glossary] (#16) is the oldest rock [pb_glossary id=\"2038\"]formation[\/pb_glossary] and the cross-cutting [pb_glossary id=\"1014\"]granite[\/pb_glossary] intrusion (#17) is younger. As seen in the figure, the other layers on the walls of the Grand Canyon are numbered in reverse order with #15 being the oldest and #1 the youngest. This illustrates the [pb_glossary id=\"2032\"]principle of superposition[\/pb_glossary]. The Grand Canyon region lies in Colorado Plateau, which is characterized by horizontal or nearly horizontal [pb_glossary id=\"1935\"]strata[\/pb_glossary], which follows the [pb_glossary id=\"2033\"]principle of original horizontality[\/pb_glossary]. These rock [pb_glossary id=\"1935\"]strata[\/pb_glossary] have been barely disturbed from their original [pb_glossary id=\"1757\"]deposition[\/pb_glossary], except by a broad regional uplift.\n\n[caption id=\"attachment_3225\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Grand_Canyon_Nonconformity.jpg\"><img class=\"wp-image-472 size-medium\" title=\"By Simeon87 (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AGrand_Canyon_with_Snow_4.JPG&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Grand_Canyon_Nonconformity-300x225.jpg\" alt=\"The red rocks are layered, the dark rocks are not.\" width=\"300\" height=\"225\"><\/a> The red, layered rocks of the Grand Canyon Supergroup overlying the dark-colored rocks of the Vishnu schist represents a type of unconformity called a nonconformity.[\/caption]The photo of the Grand Canyon here show [pb_glossary id=\"1935\"]strata[\/pb_glossary] that were originally deposited in a flat layer on top of older [pb_glossary id=\"1753\"]igneous[\/pb_glossary] and [pb_glossary id=\"1992\"]metamorphic[\/pb_glossary] \u201c[pb_glossary id=\"1935\"]basement[\/pb_glossary]\u201d rocks, per the [pb_glossary id=\"2033\"]original horizontality[\/pb_glossary] principle. Because the [pb_glossary id=\"2038\"]formation[\/pb_glossary] of the [pb_glossary id=\"1023\"]basement[\/pb_glossary] rocks and the [pb_glossary id=\"1757\"]deposition[\/pb_glossary] of the overlying [pb_glossary id=\"1935\"]strata[\/pb_glossary] is not continuous but broken by events of [pb_glossary id=\"1992\"]metamorphism[\/pb_glossary], intrusion, and [pb_glossary id=\"1755\"]erosion[\/pb_glossary], the contact between the [pb_glossary id=\"1935\"]strata[\/pb_glossary] and the older [pb_glossary id=\"1023\"]basement[\/pb_glossary] is termed an <strong>[pb_glossary id=\"2039\"]unconformity[\/pb_glossary]<\/strong>. An [pb_glossary id=\"2039\"]unconformity[\/pb_glossary] represents a [pb_glossary id=\"1244\"]period[\/pb_glossary] during which [pb_glossary id=\"1757\"]deposition[\/pb_glossary] did not occur or [pb_glossary id=\"1755\"]erosion[\/pb_glossary] removed rock that had been deposited, so there are no rocks that represent events of Earth history during that span of time at that place. [pb_glossary id=\"2039\"]Unconformities[\/pb_glossary] appear in cross sections and [pb_glossary id=\"1937\"]stratigraphic[\/pb_glossary] columns as wavy lines between [pb_glossary id=\"2038\"]formations[\/pb_glossary]. [pb_glossary id=\"2039\"]Unconformities[\/pb_glossary] are discussed in the next section.\n<h3><b>7.1.3 Unconformities<\/b><\/h3>\n[caption id=\"attachment_3226\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon.jpg\"><img class=\"wp-image-473 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon-300x225.jpg\" alt=\"The three rock layers are shown.\" width=\"300\" height=\"225\"><\/a> All three of these formations have a disconformity at the two contacts between them. The pinching Temple Butte is the easiest to see the erosion, but even between the Muav and Redwall, there is an unconfomity.[\/caption]\n\nThere are three types of [pb_glossary id=\"2039\"]unconformities[\/pb_glossary], [pb_glossary id=\"2040\"]nonconformity[\/pb_glossary], [pb_glossary id=\"2041\"]disconformity[\/pb_glossary], and [pb_glossary id=\"2042\"]angular unconformity[\/pb_glossary]. A [pb_glossary id=\"2040\"]nonconformity[\/pb_glossary] occurs when [pb_glossary id=\"1761\"]sedimentary rock[\/pb_glossary] is deposited on top of [pb_glossary id=\"1753\"]igneous[\/pb_glossary] and [pb_glossary id=\"1992\"]metamorphic[\/pb_glossary] rocks as is the case with the contact between the [pb_glossary id=\"1935\"]strata[\/pb_glossary] and [pb_glossary id=\"1023\"]basement[\/pb_glossary] rocks at the bottom of the Grand Canyon.\n\nThe [pb_glossary id=\"1935\"]strata[\/pb_glossary] in the Grand Canyon represent alternating [pb_glossary id=\"1961\"]marine[\/pb_glossary] [pb_glossary id=\"1972\"]transgressions[\/pb_glossary]\u00a0and [pb_glossary id=\"1973\"]regressions[\/pb_glossary] where sea level rose and fell over millions of years. When the sea level was high [pb_glossary id=\"1961\"]marine[\/pb_glossary] [pb_glossary id=\"1935\"]strata[\/pb_glossary] formed. When sea-level fell, the land was exposed to [pb_glossary id=\"1755\"]erosion[\/pb_glossary] creating an [pb_glossary id=\"2039\"]unconformity[\/pb_glossary]. In the Grand Canyon cross-section, this [pb_glossary id=\"1755\"]erosion[\/pb_glossary] is shown as heavy wavy lines between the various numbered [pb_glossary id=\"1935\"]strata[\/pb_glossary]. This is a type of [pb_glossary id=\"2039\"]unconformity[\/pb_glossary] called a <strong>[pb_glossary id=\"2041\"]disconformity[\/pb_glossary]<\/strong>, where either non-[pb_glossary id=\"1757\"]deposition[\/pb_glossary] or [pb_glossary id=\"1755\"]erosion[\/pb_glossary] took place. In other words, layers of rock that could have been present, are absent. The time that could have been represented by such layers is instead represented by the [pb_glossary id=\"2041\"]disconformity[\/pb_glossary]. Disconformities are [pb_glossary id=\"2039\"]unconformities[\/pb_glossary] that occur between parallel layers of [pb_glossary id=\"1935\"]strata[\/pb_glossary] indicating either a [pb_glossary id=\"1244\"]period[\/pb_glossary] of no [pb_glossary id=\"1757\"]deposition[\/pb_glossary] or [pb_glossary id=\"1755\"]erosion[\/pb_glossary].\n\n[caption id=\"attachment_3227\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/View_from_Lipan_Point.jpg\"><img class=\"wp-image-474 size-medium\" title=\"By Doug Dolde \/ Doug Dolde at en.wikipedia (Contax 645, 140mm, Leaf Aptus 75S) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AView_from_Lipan_Point.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/View_from_Lipan_Point-300x224.jpg\" alt=\"The rocks are mostly red.\" width=\"300\" height=\"224\"><\/a> In the lower part of the picture is an angular unconformity in the Grand Canyon known as the Great Unconformity. Notice flat lying strata over dipping strata (Source: Doug Dolde).[\/caption]The [pb_glossary id=\"1269\"]Phanerozoic[\/pb_glossary] [pb_glossary id=\"1935\"]strata[\/pb_glossary] in most of the Grand Canyon are horizontal. \u00a0However, near the bottom horizontal [pb_glossary id=\"1935\"]strata[\/pb_glossary] overlie tilted [pb_glossary id=\"1935\"]strata[\/pb_glossary]. This is known as the Great [pb_glossary id=\"2039\"]Unconformity[\/pb_glossary] and is an example of an <strong>[pb_glossary id=\"2042\"]angular unconformity[\/pb_glossary]<\/strong>. The lower [pb_glossary id=\"1935\"]strata[\/pb_glossary] were tilted by [pb_glossary id=\"1654\"]tectonic[\/pb_glossary] processes that disturbed their [pb_glossary id=\"2033\"]original horizontality[\/pb_glossary] and caused the [pb_glossary id=\"1935\"]strata[\/pb_glossary] to be eroded. Later, horizontal [pb_glossary id=\"1935\"]strata[\/pb_glossary] were deposited on top of the tilted [pb_glossary id=\"1935\"]strata[\/pb_glossary] creating the [pb_glossary id=\"2042\"]angular unconformity[\/pb_glossary].\n\nHere are three graphical illustrations of the three types of [pb_glossary id=\"2039\"]unconformity[\/pb_glossary].\n\n[caption id=\"attachment_3228\" align=\"alignleft\" width=\"165\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Disconformity.jpg\"><img class=\"wp-image-475\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Disconformity-300x227.jpg\" alt=\"A disconformity occurs where there is non-deposition or erosion between parallel layers in a depositional sequence\" width=\"165\" height=\"125\"><\/a> Disconformity[\/caption]\n\n<strong>[pb_glossary id=\"2041\"]Disconformity[\/pb_glossary]<\/strong>, where is a break or stratigraphic absence between [pb_glossary id=\"1935\"]strata[\/pb_glossary] in an otherwise parallel sequence of [pb_glossary id=\"1935\"]strata[\/pb_glossary].\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n\n[caption id=\"attachment_3229\" align=\"alignleft\" width=\"165\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Nonconformity.jpg\"><img class=\"wp-image-476\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nonconformity-300x226.jpg\" alt=\"A nonconformity occurs where sedimentary strata are deposited on crystalline rocks\" width=\"165\" height=\"124\"><\/a> Nonconformity (the lower rocks are igneous or metamorphic)[\/caption]\n\n<strong>[pb_glossary id=\"2040\"]Nonconformity[\/pb_glossary]<\/strong>, where sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary] are deposited on crystalline ([pb_glossary id=\"1753\"]igneous[\/pb_glossary]\u00a0or [pb_glossary id=\"1992\"]metamorphic[\/pb_glossary]) rocks.\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n\n[caption id=\"attachment_3230\" align=\"alignleft\" width=\"165\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Angular-unconformity.jpg\"><img class=\"wp-image-477\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Angular-unconformity-300x227.jpg\" alt=\"An angular unconformity develops where sedimentary strata are deposited on strata that have been deformed.\" width=\"165\" height=\"125\"><\/a> Angular unconformity[\/caption]\n\n<strong>[pb_glossary id=\"2042\"]Angular unconformity[\/pb_glossary]<\/strong>, where sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary] are deposited on a terrain developed on sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary] that have been deformed by tilting, folding, and\/or [pb_glossary id=\"2143\"]faulting[\/pb_glossary]. so that they are no longer horizontal.\n<h3><\/h3>\n<h3><\/h3>\n<h3><\/h3>\n<h3><\/h3>\n&nbsp;\n<h3><span style=\"font-weight: 400\">7.1.3 Applying Relative Dating Principles<\/span><\/h3>\n[caption id=\"attachment_3231\" align=\"alignright\" width=\"474\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.4_Block_diagram.jpg\"><img class=\"wp-image-478\" title=\"By Woudloper (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/1.0&quot;>CC BY-SA 1.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ACross-cutting_relations.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Block_diagram-300x159.jpg\" alt=\"The diagram shows many different layers\" width=\"474\" height=\"251\"><\/a> Block diagram to apply relative dating principles. The wavy rock is a old metamorphic gneiss, A and F are faults, B is an igneous granite, D is a basaltic dike, and C and E are sedimentary strata.[\/caption]In the block diagram, the sequence of geological events can be determined by using the relative-dating principles and known properties of [pb_glossary id=\"1753\"]igneous[\/pb_glossary], sedimentary, [pb_glossary id=\"1762\"]metamorphic rock[\/pb_glossary] (see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>, <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">Chapter 5<\/a>, and <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/6-metamorphic-rocks\/\">Chapter 6<\/a>). The sequence begins with the folded [pb_glossary id=\"1992\"]metamorphic[\/pb_glossary] [pb_glossary id=\"2010\"]gneiss[\/pb_glossary] on the bottom. Next, the gneiss is cut and displaced by the [pb_glossary id=\"2143\"]fault[\/pb_glossary] labeled A. Both the [pb_glossary id=\"2010\"]gneiss[\/pb_glossary] and [pb_glossary id=\"2143\"]fault[\/pb_glossary] A are cut by the [pb_glossary id=\"1753\"]igneous[\/pb_glossary] granitic intrusion called [pb_glossary id=\"1020\"]batholith[\/pb_glossary] B; its irregular outline suggests it is an [pb_glossary id=\"1753\"]igneous[\/pb_glossary] granitic intrusion emplaced as [pb_glossary id=\"1750\"]magma[\/pb_glossary] into the [pb_glossary id=\"2010\"]gneiss[\/pb_glossary]. Since [pb_glossary id=\"1020\"]batholith[\/pb_glossary] B cuts both the [pb_glossary id=\"2010\"]gneiss[\/pb_glossary] and [pb_glossary id=\"2143\"]fault[\/pb_glossary] A, [pb_glossary id=\"1020\"]batholith[\/pb_glossary] B is younger than the other two rock [pb_glossary id=\"2038\"]formations[\/pb_glossary]. Next, the [pb_glossary id=\"2010\"]gneiss[\/pb_glossary], [pb_glossary id=\"2143\"]fault[\/pb_glossary] A, and [pb_glossary id=\"1020\"]batholith[\/pb_glossary] B were eroded forming a [pb_glossary id=\"2040\"]nonconformity[\/pb_glossary] as shown with the wavy line. This [pb_glossary id=\"2039\"]unconformity[\/pb_glossary] was actually an ancient landscape surface on which [pb_glossary id=\"1761\"]sedimentary rock[\/pb_glossary] C was subsequently deposited perhaps by a [pb_glossary id=\"1961\"]marine[\/pb_glossary] [pb_glossary id=\"1972\"]transgression[\/pb_glossary]. Next, [pb_glossary id=\"1753\"]igneous[\/pb_glossary] basaltic [pb_glossary id=\"1021\"]dike[\/pb_glossary] D cut through all rocks except [pb_glossary id=\"1761\"]sedimentary rock[\/pb_glossary] E. This shows that there is a [pb_glossary id=\"2041\"]disconformity[\/pb_glossary] between sedimentary rocks C and E. The top of [pb_glossary id=\"1021\"]dike[\/pb_glossary] D is level with the top of layer C, which establishes that [pb_glossary id=\"1755\"]erosion[\/pb_glossary] flattened the landscape prior to the [pb_glossary id=\"1757\"]deposition[\/pb_glossary] of layer E, creating a [pb_glossary id=\"2041\"]disconformity[\/pb_glossary] between rocks D and E. [pb_glossary id=\"2143\"]Fault[\/pb_glossary] F cuts across all of the older rocks B, C and E, producing a [pb_glossary id=\"2185\"]fault scarp[\/pb_glossary], which is the low ridge on the upper-left side of the diagram. The final events affecting this area are current [pb_glossary id=\"1755\"]erosion[\/pb_glossary] processes working on the land surface, [pb_glossary id=\"1908\"]rounding[\/pb_glossary] off the edge of the [pb_glossary id=\"2185\"]fault scarp[\/pb_glossary], and producing the modern landscape at the top of the diagram.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"43\"]\n\n[caption id=\"attachment_4083\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/7.1-Did-I-Get-It-QR-Code.png\"><img class=\"wp-image-479 size-thumbnail\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 7.1 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">7.2 Absolute Dating<\/span><\/h2>\n[caption id=\"attachment_3232\" align=\"alignleft\" width=\"407\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Nuvvuagittuq_belt_rocks.jpg\"><img class=\"wp-image-480\" title=\"NASA, public domain\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nuvvuagittuq_belt_rocks-300x225.jpg\" alt=\"It shows rocks on a shoreline.\" width=\"407\" height=\"305\"><\/a> Canada's Nuvvuagittuq Greenstone Belt may have the oldest rocks and oldest evidence life on Earth, according to recent studies.[\/caption]\n\nRelative time allows scientists to tell the story of Earth events, but does not provide specific numeric ages, and thus, the rate at which geologic processes operate. Based on Hutton\u2019s [pb_glossary id=\"1736\"]principle of uniformitarianism[\/pb_glossary] (see <a href=\"#14_Foundations_of_Modern_Geology\">Chapter 1<\/a>), early geologists surmised geological processes work slowly and the Earth is very old. [pb_glossary id=\"2031\"]Relative dating[\/pb_glossary] principles was how scientists interpreted Earth history until the end of the 19th Century. Because science advances as technology advances, the discovery of [pb_glossary id=\"2044\"]radioactivity[\/pb_glossary] in the late 1800s provided scientists with a new scientific tool called <strong>radioisotopic dating<\/strong>. Using this new technology, they could assign specific time units, in this case years, to [pb_glossary id=\"1765\"]mineral[\/pb_glossary] grains within a rock. These numerical values are not dependent on comparisons with other rocks such as with [pb_glossary id=\"2031\"]relative dating[\/pb_glossary], so this dating method is called <strong>[pb_glossary id=\"2043\"]absolute dating[\/pb_glossary]<\/strong>. There are several types of [pb_glossary id=\"2043\"]absolute dating[\/pb_glossary] discussed in this section but radioisotopic dating is the most common and therefore is the [pb_glossary id=\"2158\"]focus[\/pb_glossary] on this section.\n<h3><b>7.2.1 Radioactive Decay<\/b><\/h3>\n[caption id=\"attachment_3233\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Isotopes-of-hydrogen.jpg\"><img class=\"wp-image-481 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Isotopes-of-hydrogen-300x154.jpg\" alt=\"Three isotopes of hydrogen differing in the number of neutrons.\" width=\"300\" height=\"154\"><\/a> Three isotopes of hydrogen[\/caption]\n\n<span style=\"font-weight: 400\">All [pb_glossary id=\"1778\"]elements[\/pb_glossary] on the Periodic Table of [pb_glossary id=\"1778\"]Elements[\/pb_glossary] (see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/3-minerals\/\">Chapter 3<\/a>) contain [pb_glossary id=\"1779\"]isotopes[\/pb_glossary]. An [pb_glossary id=\"1779\"]isotope[\/pb_glossary] is an atom of an [pb_glossary id=\"1778\"]element[\/pb_glossary] with a different number of neutrons. For example, hydrogen (H) always has 1 proton in its nucleus (the atomic number), but the number of neutrons can vary among the [pb_glossary id=\"1779\"]isotopes[\/pb_glossary] (0, 1, 2). Recall that the number of neutrons added to the atomic number gives the atomic mass. When hydrogen has 1 proton and 0 neutrons it is sometimes called protium (<sup>1<\/sup>H<\/span><span style=\"font-weight: 400\">), when hydrogen has 1 proton and 1 neutron it is called deuterium (<sup>2<\/sup>H<\/span><span style=\"font-weight: 400\">), and when hydrogen has 1 proton and 2 neutrons it is called tritium (<sup>3<\/sup>H<\/span><span style=\"font-weight: 400\">).<\/span>\n\nMany [pb_glossary id=\"1778\"]elements[\/pb_glossary] have both stable and unstable [pb_glossary id=\"1779\"]isotopes[\/pb_glossary]. For the hydrogen example, <sup>1<\/sup>H and <sup>2<\/sup>H are stable, but <sup>3<\/sup>H is unstable. Unstable [pb_glossary id=\"1779\"]isotopes[\/pb_glossary], called <strong>[pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"1779\"]isotopes[\/pb_glossary]<\/strong>, spontaneously decay over time releasing subatomic particles or energy in a process called <strong>[pb_glossary id=\"2044\"]radioactive[\/pb_glossary] decay<\/strong>. When this occurs, an unstable [pb_glossary id=\"1779\"]isotope[\/pb_glossary] becomes a more stable [pb_glossary id=\"1779\"]isotope[\/pb_glossary] of another [pb_glossary id=\"1778\"]element[\/pb_glossary]. For example, carbon-14 (<sup>14<\/sup>C) decays to nitrogen-14 (<sup>14<\/sup>N).\n\n[caption id=\"attachment_3234\" align=\"alignleft\" width=\"140\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Halflife-sim.gif\"><img class=\"wp-image-482\" title=\"By Sbyrnes321 (Own work) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AHalflife-sim.gif&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Halflife-sim.gif\" alt=\"The many looks more smooth\" width=\"140\" height=\"263\"><\/a> Simulation of half-life. On the left, 4 simulations with only a few atoms. On the right, 4 simulations with many atoms.[\/caption]&nbsp;\n\nThe [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] decay of any individual atom is a completely unpredictable and random event. However, some rock specimens have an enormous number of [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"1779\"]isotopes[\/pb_glossary], perhaps trillions of atoms, and this large group of [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"1779\"]isotopes[\/pb_glossary] does have a predictable pattern of [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] decay. The [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] decay of <em>half<\/em> of the [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"1779\"]isotopes[\/pb_glossary] in this group takes a specific amount of time. The time it takes for half of the atoms in a substance to decay is called the <strong>[pb_glossary id=\"2045\"]half-life[\/pb_glossary]<\/strong>. In other words, the [pb_glossary id=\"2045\"]half-life[\/pb_glossary] of an [pb_glossary id=\"1779\"]isotope[\/pb_glossary] is the amount of time it takes for half of a group of unstable [pb_glossary id=\"1779\"]isotopes[\/pb_glossary] to decay to a stable [pb_glossary id=\"1779\"]isotope[\/pb_glossary]. The [pb_glossary id=\"2045\"]half-life[\/pb_glossary] is constant and measurable for a given [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"1779\"]isotope[\/pb_glossary], so it can be used to calculate the age of a rock. For example, the [pb_glossary id=\"2045\"]half-life[\/pb_glossary] uranium-238 (<sup>238<\/sup>U) is 4.5 billion years and the [pb_glossary id=\"2045\"]half-life[\/pb_glossary] of <sup>14<\/sup>C is 5,730 years.\n\nThe principles behind this dating method require two key assumptions. First, the [pb_glossary id=\"1765\"]mineral[\/pb_glossary] grains containing the [pb_glossary id=\"1779\"]isotope[\/pb_glossary] formed at the same time as the rock, such as [pb_glossary id=\"1765\"]minerals[\/pb_glossary] in an [pb_glossary id=\"1753\"]igneous rock[\/pb_glossary] that crystallized from [pb_glossary id=\"1750\"]magma[\/pb_glossary]. Second, the [pb_glossary id=\"1765\"]mineral[\/pb_glossary] crystals remain a closed [pb_glossary id=\"1742\"]system[\/pb_glossary], meaning they are not subsequently altered by [pb_glossary id=\"1778\"]elements[\/pb_glossary] moving in or out of them.\n\n[caption id=\"attachment_3152\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.1-03-Granite-vs-Gneiss.jpg\"><img class=\"wp-image-434 size-medium\" title=\"Source: Peter Davis\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/06.1-03-Granite-vs-Gneiss-300x130.jpg\" alt=\"Two rocks with very similar colors. One is a granite and another is a gneiss that has aligned dark minerals.\" width=\"300\" height=\"130\"><\/a> Granite (left) and gneiss (right). Dating a mineral within the granite would give the crystallization age of the rock, while dating the gneiss might reflect the timing of metamorphism.[\/caption]\n\nThese requirements place some constraints on the kinds of rock suitable for dating, with [pb_glossary id=\"1753\"]igneous rock[\/pb_glossary] being the best. [pb_glossary id=\"1992\"]Metamorphic[\/pb_glossary] rocks are crystalline, but the processes of [pb_glossary id=\"1762\"]metamorphism[\/pb_glossary] may reset the clock and derived ages may represent a smear of different [pb_glossary id=\"1992\"]metamorphic[\/pb_glossary] events rather than the age of original [pb_glossary id=\"1752\"]crystallization[\/pb_glossary]. [pb_glossary id=\"2441\"]Detrital[\/pb_glossary] sedimentary rocks contain clasts from separate [pb_glossary id=\"1766\"]parent rocks[\/pb_glossary] from unknown locations and derived ages are thus meaningless. However, sedimentary rocks with [pb_glossary id=\"1785\"]precipitated[\/pb_glossary] [pb_glossary id=\"1765\"]minerals[\/pb_glossary], such as [pb_glossary id=\"1920\"]evaporites[\/pb_glossary], may contain [pb_glossary id=\"1778\"]elements[\/pb_glossary] suitable for radioisotopic dating. [pb_glossary id=\"1753\"]Igneous[\/pb_glossary] [pb_glossary id=\"1004\"]pyroclastic[\/pb_glossary] layers and [pb_glossary id=\"1751\"]lava[\/pb_glossary]<span style=\"font-size: 1em\">\u00a0flows within a sedimentary sequence can be used to date the sequence. Cross-cutting [pb_glossary id=\"1753\"]igneous[\/pb_glossary] rocks and [pb_glossary id=\"1022\"]sills[\/pb_glossary] can be used to bracket the ages of affected, older sedimentary rocks. The resistant [pb_glossary id=\"1765\"]mineral[\/pb_glossary] [pb_glossary id=\"1227\"]zircon[\/pb_glossary], found as clasts in many ancient sedimentary rocks, has been successfully used for establishing very old dates, including the age of Earth\u2019s oldest known rocks. Knowing that [pb_glossary id=\"1227\"]zircon[\/pb_glossary] [pb_glossary id=\"1765\"]minerals[\/pb_glossary] in metamorphosed [pb_glossary id=\"1756\"]sediments[\/pb_glossary] came from older rocks that are no longer available for study, scientists can date [pb_glossary id=\"1227\"]zircon[\/pb_glossary] to establish the age of the pre-[pb_glossary id=\"1992\"]metamorphic[\/pb_glossary] [pb_glossary id=\"2418\"]source rocks[\/pb_glossary].<\/span>\n\n[caption id=\"attachment_3236\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Alpha_Decay.svg_.png\"><img class=\"wp-image-483 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Alpha_Decay.svg_-300x204.png\" alt=\"Two protons and two neutrons leave the nucleus.\" width=\"300\" height=\"204\"><\/a> An alpha decay: Two protons and two neutrons leave the nucleus.[\/caption]\n\nThere are several ways [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] atoms decay.\u00a0 We will consider three of them here\u2014<b>[pb_glossary id=\"2046\"]alpha decay[\/pb_glossary], [pb_glossary id=\"1223\"]beta decay[\/pb_glossary], <\/b>and<b> [pb_glossary id=\"1225\"]electron capture[\/pb_glossary]<\/b><span style=\"font-weight: 400\">. <\/span><strong>[pb_glossary id=\"2046\"]Alpha decay[\/pb_glossary]<\/strong> is when an alpha particle, which consists of two protons and two neutrons, is emitted from the nucleus of an atom. This also happens to be the nucleus of a helium atom; helium gas may get trapped in the crystal lattice of a [pb_glossary id=\"1765\"]mineral[\/pb_glossary] in which [pb_glossary id=\"2046\"]alpha decay[\/pb_glossary] has taken place. When an atom loses two protons from its nucleus, lowering its atomic number, it is transformed into an [pb_glossary id=\"1778\"]element[\/pb_glossary] that is two atomic numbers lower on the Periodic Table of the [pb_glossary id=\"1778\"]Elements[\/pb_glossary].\n\n[caption id=\"attachment_3237\" align=\"alignright\" width=\"477\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.11_periodic_table.png\"><img class=\"wp-image-484\" title=\"By Sandbh (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0&quot;>CC BY-SA 4.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3APeriodic_Table_Chart.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.11_periodic_table-300x160.png\" alt=\"Simplified Periodic Table of the Elements\" width=\"477\" height=\"254\"><\/a> Periodic Table of the Elements[\/caption]The loss of four particles, in this case two neutrons and two protons, also lowers the mass of the atom by four. For example [pb_glossary id=\"2046\"]alpha decay[\/pb_glossary] takes place in the unstable [pb_glossary id=\"1779\"]isotope[\/pb_glossary] <sup>238<\/sup>U, which has an atomic number of 92 (92 protons) and mass number of 238 (total of all protons and neutrons). When <sup>238<\/sup>U spontaneously emits an alpha particle, it becomes thorium-234 (<sup>234<\/sup>Th). The [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] decay product of an [pb_glossary id=\"1778\"]element[\/pb_glossary] is called its <strong>[pb_glossary id=\"1222\"]daughter isotope[\/pb_glossary]<\/strong> and the original [pb_glossary id=\"1778\"]element[\/pb_glossary] is called the <strong>[pb_glossary id=\"2047\"]parent isotope[\/pb_glossary]<\/strong>. In this case, <sup>238<\/sup>U is the [pb_glossary id=\"2047\"]parent isotope[\/pb_glossary] and <sup>234<\/sup>Th is the [pb_glossary id=\"1222\"]daughter isotope[\/pb_glossary]. The [pb_glossary id=\"2045\"]half-life[\/pb_glossary] of <sup>238<\/sup>U is 4.5 billion years, i.e., the time it takes for half of the [pb_glossary id=\"2047\"]parent isotope[\/pb_glossary] atoms to decay into the [pb_glossary id=\"1222\"]daughter isotope[\/pb_glossary]. This isotope of uranium, <sup>238<\/sup>U, can be used for [pb_glossary id=\"2043\"]absolute dating[\/pb_glossary] the oldest materials found on Earth, and even [pb_glossary id=\"1254\"]meteorites[\/pb_glossary]\u00a0and materials from the earliest events in our [pb_glossary id=\"1253\"]solar system[\/pb_glossary].\n\n[caption id=\"attachment_3238\" align=\"alignleft\" width=\"198\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/U-238-decay-chain.jpg\"><img class=\"wp-image-485 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/U-238-decay-chain-198x300.jpg\" alt=\"Decay chain of U-238 to stable Pb-206 through a series of alpha and beta decays.\" width=\"198\" height=\"300\"><\/a> Decay chain of U-238 to stable Pb-206 through a series of alpha and beta decays.[\/caption]\n\n<b>B<\/b>\n\n[pb_glossary id=\"1223\"]Beta decay[\/pb_glossary] is when a neutron in its nucleus splits into an electron and a proton. The electron is emitted from the nucleus as a beta ray. The new proton increases the [pb_glossary id=\"1778\"]element[\/pb_glossary]\u2019s atomic number by one, forming a new [pb_glossary id=\"1778\"]element[\/pb_glossary] with the same atomic mass as the [pb_glossary id=\"2047\"]parent isotope[\/pb_glossary]. For example, <sup>234<\/sup>Th is unstable and undergoes [pb_glossary id=\"1223\"]beta decay[\/pb_glossary] to form protactinium-234 (<sup>234<\/sup>Pa), which also undergoes [pb_glossary id=\"1223\"]beta decay[\/pb_glossary] to form uranium-234 (<sup>234<\/sup>U). Notice these are all [pb_glossary id=\"4207\"]isotopes[\/pb_glossary] of different [pb_glossary id=\"1778\"]elements[\/pb_glossary] but they have the same atomic mass of 234. The decay process of [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"1778\"]elements[\/pb_glossary] like uranium keeps producing [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"2047\"]parents[\/pb_glossary] and [pb_glossary id=\"1222\"]daughters[\/pb_glossary] until a stable, or non-[pb_glossary id=\"2044\"]radioactive[\/pb_glossary], daughter is formed. Such a series is called a <strong>[pb_glossary id=\"1224\"]decay chain[\/pb_glossary]<\/strong>. The [pb_glossary id=\"1224\"]decay chain[\/pb_glossary] of the [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"2047\"]parent isotope[\/pb_glossary] <sup>238<\/sup>U progresses through a series of alpha (red arrows on the adjacent figure) and beta decays (blue arrows), until it forms the stable [pb_glossary id=\"1222\"]daughter isotope[\/pb_glossary], lead-206 (<sup>206<\/sup>Pb).\n\n[caption id=\"attachment_3239\" align=\"alignright\" width=\"254\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Atomic_rearrangement_following_an_electron_capture.svg_.png\"><img class=\"wp-image-486 size-medium\" title=\"By Pamputt (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0&quot;>CC BY-SA 4.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AAtomic_rearrangement_following_an_electron_capture.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Atomic_rearrangement_following_an_electron_capture.svg_-254x300.png\" alt=\"It shows two paths\" width=\"254\" height=\"300\"><\/a> The two paths of electron capture[\/caption]<span style=\"font-weight: 400\"><strong>[pb_glossary id=\"1225\"]Electron capture[\/pb_glossary]<\/strong> is when a proton in the nucleus captures an electron from one of the electron shells and becomes a neutron. This produces one of two different effects: 1) an electron jumps in to fill the missing spot of the departed electron and emits an X-ray, or 2) in what is called the Auger process, another electron is released and changes the atom into an [pb_glossary id=\"2449\"]ion[\/pb_glossary]. The atomic number is reduced by one and mass number remains the same. An example of an [pb_glossary id=\"1778\"]element[\/pb_glossary] that decays by [pb_glossary id=\"1225\"]electron capture[\/pb_glossary] is potassium-40 (<sup>40<\/sup>K). [pb_glossary id=\"2044\"]Radioactive[\/pb_glossary] <sup>40<\/sup>K makes up a tiny percentage (0.012%) of naturally occurring potassium, most of which not [pb_glossary id=\"2044\"]radioactive[\/pb_glossary]. <sup>40<\/sup>K decays to argon-40 (<sup>40<\/sup>Ar) with a [pb_glossary id=\"2045\"]half-life[\/pb_glossary] of 1.25 billion years, so it is very useful for dating geological events<\/span><span style=\"font-weight: 400\">. <\/span>Below is a table of some of the more commonly-used [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] dating [pb_glossary id=\"1779\"]isotopes[\/pb_glossary] and their half-lives.\n<table>\n<tbody>\n<tr>\n<td><b>[pb_glossary id=\"1778\"]Elements[\/pb_glossary]<\/b><\/td>\n<td><b>Parent symbol<\/b><\/td>\n<td><b>Daughter symbol<\/b><\/td>\n<td><b>[pb_glossary id=\"2045\"]Half-life[\/pb_glossary]<\/b><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Uranium-238\/Lead-206<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>238<\/sup>U<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>206<\/sup>Pb<\/span><\/td>\n<td><span style=\"font-weight: 400\">4.5 billion years<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Uranium-235\/Lead-207<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>235<\/sup>U<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>207<\/sup>Pb<\/span><\/td>\n<td><span style=\"font-weight: 400\">704 million years<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Potassium-40\/Argon-40<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>40<\/sup>K<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>40<\/sup>Ar<\/span><\/td>\n<td><span style=\"font-weight: 400\">1.25 billion years<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Rubidium-87\/Strontium-87<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>87<\/sup>Rb<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>87<\/sup>Sr<\/span><\/td>\n<td><span style=\"font-weight: 400\">48.8 billion years<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Carbon-14\/Nitrogen-14<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>14<\/sup>C<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>14<\/sup>N<\/span><\/td>\n<td><span style=\"font-weight: 400\">5,730 years<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<em>Some common [pb_glossary id=\"1779\"]<em>isotopes<\/em>[\/pb_glossary] used for radioisotopic dating.<\/em>\n<h3><b>7.2.2 Radioisotopic Dating<\/b><\/h3>\n[caption id=\"attachment_3240\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.14_Mass_spectrometer.jpg\"><img class=\"wp-image-487 size-medium\" title=\"This is a copyrighted image from the CAMECA Archives Reproduction is authorized, under the terms of the GNU Free Documentation License.\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.14_Mass_spectrometer-300x213.jpg\" alt=\"Photo of mass spectrometer\" width=\"300\" height=\"213\"><\/a> Mass spectrometer instrument[\/caption]\n\nFor a given a sample of rock, how is the dating procedure carried out? The parent and [pb_glossary id=\"1222\"]daughter isotopes[\/pb_glossary]\u00a0are separated out of the [pb_glossary id=\"1765\"]mineral[\/pb_glossary] using chemical extraction. In the case of uranium, <sup>238<\/sup>U and <sup>235<\/sup>U [pb_glossary id=\"1779\"]isotopes[\/pb_glossary] are separated out together, as are the <sup>206<\/sup>Pb and <sup>207<\/sup>Pb with an instrument called a [pb_glossary id=\"1226\"]mass spectrometer[\/pb_glossary]<span style=\"font-weight: 400\">.\u00a0<\/span>\n\n[caption id=\"attachment_3241\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Half_times.svg_.png\"><img class=\"wp-image-488 size-medium\" title=\"By Krishnavedala (Own work) [<a href=&quot;http:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en&quot;>CC0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AHalf_times.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Half_times.svg_-300x300.png\" alt=\"The graph gets progressively taller\" width=\"300\" height=\"300\"><\/a> Graph of amount of half life vs. amount of daughter isotope.[\/caption]Here is a simple example of age calculation using the daughter-to-parent ratio of [pb_glossary id=\"1779\"]isotopes[\/pb_glossary]. When the [pb_glossary id=\"1765\"]mineral[\/pb_glossary] initially forms, it consists of 0% daughter and 100% [pb_glossary id=\"2047\"]parent isotope[\/pb_glossary], so the daughter-to-parent ratio (D\/P) is 0. After one [pb_glossary id=\"2045\"]half-life[\/pb_glossary], half the parent has decayed so there is 50% daughter and 50% parent, a 50\/50 ratio, with D\/P = 1. After two <u>half-lives<\/u>, there is 75% daughter and 25% parent (75\/25 ratio) and D<u>\/P = <\/u>3. This can be further calculated for a series of half-lives as shown in the table. The table does not show more than 10 half-lives because after about 10 half-lives, the amount of remaining parent is so small it becomes too difficult to accurately measure via chemical analysis. Modern applications of this method have achieved remarkable accuracies of plus or minus two million years in 2.5 billion years (that\u2019s \u00b10.055%). Applying the uranium\/lead technique in any given sample analysis provides two separate clocks running at the same time, <sup>238<\/sup>U and <sup>235<\/sup>U. The existence of these two clocks in the same sample gives a cross-check between the two. Many geological samples contain multiple parent\/daughter pairs, so cross-checking the clocks confirms that radioisotopic dating is highly reliable.\n<table>\n<tbody>\n<tr style=\"height: 111px\">\n<td style=\"height: 111px\"><b>Half-lives<\/b>\n\n<b>(#)<\/b><\/td>\n<td style=\"height: 111px\"><b>Parent present (%)<\/b><\/td>\n<td style=\"height: 111px\"><b>Daughter present <\/b>\n\n<b>(%)<\/b><\/td>\n<td style=\"height: 111px\"><b>Daughter\/<\/b>\n\n<b>Parent ratio<\/b><\/td>\n<td style=\"height: 111px\"><b>Parent\/ <\/b>\n\n<b>Daughter ratio<\/b><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">Start the clock<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">100<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0<\/span><\/td>\n<td style=\"height: 27px\">\u00a0infinite<\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">1<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">50<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">50<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">1<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">1<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">2<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">25<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">75<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">3<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.33<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">3<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">12.5<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">87.5<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">7<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.143<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">4<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">6.25<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">93.75<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">15<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.0667<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27.9277px\">\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">5<\/span><\/td>\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">3.125<\/span><\/td>\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">96.875<\/span><\/td>\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">31<\/span><\/td>\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">0.0325<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">10<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.098<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">99.9<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">1023<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.00098<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<em>Ratio of parent to daughter in terms of [pb_glossary id=\"2045\"]<em>half-life<\/em>[\/pb_glossary].<\/em>\n\n[caption id=\"attachment_3242\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Accelerator_mass_spectrometer_schematic_for_radiocarbon.svg_.png\"><img class=\"wp-image-489 size-medium\" title=\"By Mike Christie (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AAccelerator_mass_spectrometer_schematic_for_radiocarbon.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Accelerator_mass_spectrometer_schematic_for_radiocarbon.svg_-300x111.png\" alt=\"It shows the isotopes separating\" width=\"300\" height=\"111\"><\/a> Schematic of carbon going through a mass spectrometer.[\/caption]<span style=\"font-weight: 400\">Another radioisotopic dating method involves carbon and is useful for dating archaeologically important samples containing organic substances like wood or bone. <strong>Radiocarbon dating<\/strong>, also called carbon dating, uses the unstable [pb_glossary id=\"1779\"]isotope[\/pb_glossary] carbon-14 (<sup>14<\/sup>C) and the stable [pb_glossary id=\"1779\"]isotope[\/pb_glossary] carbon-12 (<sup>12<\/sup>C). Carbon-14 is constantly being created in the [pb_glossary id=\"1745\"]atmosphere[\/pb_glossary] by the interaction of cosmic particles with atmospheric nitrogen-14 (<sup>14<\/sup>N)<\/span><span style=\"font-weight: 400\">. Cosmic particles such as neutrons [pb_glossary id=\"500\"]strike[\/pb_glossary] the nitrogen nucleus, kicking out a proton but leaving the neutron in the nucleus. The [pb_glossary id=\"1698\"]collision[\/pb_glossary] reduces the atomic number by one, changing it from seven to six, changing the nitrogen into carbon with the same mass number of 14. The <sup>14<\/sup>C quickly [pb_glossary id=\"1781\"]bonds[\/pb_glossary] with oxygen (O) in the [pb_glossary id=\"1745\"]atmosphere[\/pb_glossary] to form carbon dioxide (<sup>14<\/sup>CO<sub>2<\/sub>) that mixes with other atmospheric carbon dioxide (<sup>12<\/sup>CO<sub>2<\/sub>) and this mix of gases is incorporated into living matter. While an organism is alive, the ratio of <sup>14<\/sup>C\/<sup>12<\/sup>C in its body doesn\u2019t really change since CO<sub>2<\/sub> is constantly exchanged with the [pb_glossary id=\"1745\"]atmosphere[\/pb_glossary]. However, when it dies, the radiocarbon clock starts ticking as the <sup>14<\/sup>C decays back to <sup>14<\/sup>N by [pb_glossary id=\"1223\"]beta decay[\/pb_glossary], which has a [pb_glossary id=\"2045\"]half-life[\/pb_glossary] of 5,730 years. The radiocarbon dating technique is thus useful for 57,300 years or so, about 10 half-lives back.<\/span>\n\n[caption id=\"attachment_3243\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Carbon_Dioxide_400kyr.png\"><img class=\"wp-image-490 size-medium\" title=\"by Robert A. Rohde\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Carbon_Dioxide_400kyr-300x218.png\" alt=\"It varies, but spikes in recent past.\" width=\"300\" height=\"218\"><\/a> Carbon dioxide concentrations over the last 400,000 years.[\/caption]\n\nRadiocarbon dating relies on daughter-to-parent ratios derived from a known quantity of parent <sup>14<\/sup>C. Early applications of carbon dating assumed the production and concentration of <sup>14<\/sup>C in the [pb_glossary id=\"1745\"]atmosphere[\/pb_glossary] remained fairly constant for the last 50,000 years. However, it is now known that the amount of parent <sup>14<\/sup>C levels in the [pb_glossary id=\"1745\"]atmosphere[\/pb_glossary] has varied. Comparisons of carbon ages with tree-ring data and other data for known events have allowed reliable calibration of the radiocarbon dating method. Taking into account carbon-14 baseline levels must be calibrated against other reliable dating methods, carbon dating has been shown to be a reliable method for dating archaeological specimens and very recent geologic events.\n<h3><b>7.2.3 Age of the Earth<\/b><\/h3>\n[caption id=\"attachment_3244\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Hadean.png\"><img class=\"wp-image-491 size-medium\" title=\"By Tim Bertelink (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0&quot;>CC BY-SA 4.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AHadean.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Hadean-300x161.png\" alt=\"The surface of Earth is full of volcanoes.\" width=\"300\" height=\"161\"><\/a> Artist\u2019s impression of Earth in the Hadean Eon, early in Earth\u2019s history.[\/caption]<span style=\"font-weight: 400\">The work of Hutton and other scientists gained attention after the Renaissance (see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/1-understanding-science\/\">Chapter 1<\/a>), spurring exploration into the idea of an ancient Earth. In the late 19<sup>th<\/sup> century William Thompson, a.k.a. Lord Kelvin, applied his knowledge of physics to develop the assumption that the Earth started as a hot molten sphere. He estimated the Earth is 98 million years old, but because of uncertainties in his calculations stated the age as a range of between 20 and 400 million years<\/span><span style=\"font-weight: 400\">. <\/span><a href=\"https:\/\/youtu.be\/mOSpRzW2i_4\">This animation<\/a> illustrates how Kelvin calculated this range and why his numbers were so far off, which has to do with unequal heat transfer within the Earth. It has also been pointed out that Kelvin failed to consider pliability and [pb_glossary id=\"1655\"]convection[\/pb_glossary] in the Earth\u2019s [pb_glossary id=\"1664\"]mantle[\/pb_glossary] as a heat transfer mechanism. Kelvin\u2019s estimate for Earth\u2019s age was considered plausible but not without challenge, and the discovery of [pb_glossary id=\"2044\"]radioactivity[\/pb_glossary] provided a more accurate method for determining ancient ages<span style=\"font-weight: 400\">.<\/span>\n\n<span style=\"font-weight: 400\">In the 1950\u2019s, Clair Patterson (1922\u20131995) thought he could determine the age of the Earth using [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"1779\"]isotopes[\/pb_glossary] from [pb_glossary id=\"1254\"]meteorites[\/pb_glossary], which he considered to be early [pb_glossary id=\"1253\"]solar system[\/pb_glossary] remnants that were present at the time Earth was forming. Patterson analyzed [pb_glossary id=\"1254\"]meteorite[\/pb_glossary] samples for uranium and lead using a [pb_glossary id=\"1226\"]mass spectrometer[\/pb_glossary]. He used the uranium\/lead dating technique in determining the age of the Earth to be 4.55 billion years, give or take about 70 million (\u00b1 1.5%). The current estimate for the age of the Earth is 4.54 billion years, give or take 50 million (\u00b1 1.1%)<\/span><span style=\"font-weight: 400\">. It is remarkable that Patterson, who was still a graduate student at the University of Chicago, came up with a result that has been little altered in over 60 years, even as technology has improved dating methods.<\/span>\n<h3><b>7.2.4 Dating Geological Events<\/b><\/h3>\n[caption id=\"attachment_3245\" align=\"alignright\" width=\"212\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.17_Zircon_microscope.jpg\"><img class=\"wp-image-492 size-medium\" title=\"Photo by Foto Chd (german wikipedia, https:\/\/de.wikipedia.org\/wiki\/Benutzer:Chd), used under the terms of the GNU Free Documentation License\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.17_Zircon_microscope-212x300.jpg\" alt=\"Photomicrograph of zircon crystal\" width=\"212\" height=\"300\"><\/a> Photomicrograph of zircon crystal[\/caption]\n\n[pb_glossary id=\"2044\"]Radioactive[\/pb_glossary] [pb_glossary id=\"1779\"]isotopes[\/pb_glossary] of[pb_glossary id=\"1765\"] elements[\/pb_glossary] that are common in [pb_glossary id=\"1765\"]mineral[\/pb_glossary] crystals are useful for radioisotopic dating. The uranium\/lead method, with its two cross-checking clocks, is most often used with crystals of the [pb_glossary id=\"1765\"]mineral[\/pb_glossary] [pb_glossary id=\"1227\"]zircon[\/pb_glossary] (ZrSiO<sub>4<\/sub>) where uranium can substitute for zirconium in the crystal lattice. [pb_glossary id=\"1227\"]Zircon[\/pb_glossary] is resistant to [pb_glossary id=\"1754\"]weathering[\/pb_glossary] which makes it useful for dating geological events in ancient rocks. During [pb_glossary id=\"1992\"]metamorphic[\/pb_glossary] events, [pb_glossary id=\"1227\"]zircon[\/pb_glossary] crystals may form multiple crystal layers, with each layer recording the isotopic age of an event, thus tracing the progress of the several [pb_glossary id=\"1992\"]metamorphic[\/pb_glossary] events<span style=\"font-weight: 400\">.\u00a0<\/span>\n\nGeologists have used [pb_glossary id=\"1227\"]zircon[\/pb_glossary] grains to do some amazing studies that illustrate how scientific conclusions can change with technological advancements. [pb_glossary id=\"1227\"]Zircon[\/pb_glossary] crystals from Western Australia that formed when the crust first differentiated from the [pb_glossary id=\"1664\"]mantle[\/pb_glossary] 4.4 billion years ago have been determined to be the oldest known rocks. The [pb_glossary id=\"1227\"]zircon[\/pb_glossary] grains were incorporated into metasedimentary host rocks, sedimentary rocks showing signs of having undergone partial metamorphism. The host rocks were not very old but the embedded zircon grains were created 4.4 billion years ago, and survived the subsequent processes of [pb_glossary id=\"1754\"]weathering[\/pb_glossary], [pb_glossary id=\"1755\"]erosion[\/pb_glossary], [pb_glossary id=\"1757\"]deposition[\/pb_glossary], and [pb_glossary id=\"1992\"]metamorphism[\/pb_glossary]. From other properties of the [pb_glossary id=\"1227\"]zircon[\/pb_glossary] crystals, researchers concluded that not only were continental rocks exposed above sea level, but also that conditions on the early Earth were cool enough for liquid water to exist on the surface. The presence of liquid water allowed the processes of weathering and erosion to take place. Researchers at UCLA studied 4.1 billion-year-old [pb_glossary id=\"1227\"]zircon[\/pb_glossary] crystals and found carbon in the [pb_glossary id=\"1227\"]zircon[\/pb_glossary] crystals that may be biogenic in origin, meaning that life may have existed on Earth much earlier than previously thought.\n\n[caption id=\"attachment_2557\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Yellowstone_volcano_-_ash_beds.jpg\"><img class=\"wp-image-134 size-medium\" title=\"Public domain, USGS\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Yellowstone_volcano_-_ash_beds-300x195.jpg\" alt=\"The eruptions trend eastward due to prevailing winds.\" width=\"300\" height=\"195\"><\/a> Several prominent ash beds found in North America, including three Yellowstone eruptions shaded pink (Mesa Falls, Huckleberry Ridge, and Lava Creek), the Bisho Tuff ash bed (brown dashed line), and the modern May 18th, 1980 ash fall (yellow).[\/caption]\n\n<span style=\"font-weight: 400\">[pb_glossary id=\"1753\"]Igneous[\/pb_glossary] rocks best suited for radioisotopic dating because their primary [pb_glossary id=\"1765\"]minerals[\/pb_glossary] provide dates of [pb_glossary id=\"1752\"]crystallization[\/pb_glossary] from [pb_glossary id=\"1750\"]magma[\/pb_glossary]. [pb_glossary id=\"1992\"]Metamorphic[\/pb_glossary] processes tend to reset the clocks and smear the [pb_glossary id=\"1753\"]igneous rock[\/pb_glossary]\u2019s original date. [pb_glossary id=\"2441\"]Detrital[\/pb_glossary] sedimentary rocks are less useful because they are made of [pb_glossary id=\"1765\"]minerals[\/pb_glossary] derived from multiple parent sources with potentially many dates. However, scientists can use [pb_glossary id=\"1753\"]igneous[\/pb_glossary] events to date sedimentary sequences. For example, if sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary] are between a [pb_glossary id=\"1751\"]lava[\/pb_glossary] flow and [pb_glossary id=\"228\"]volcanic[\/pb_glossary] [pb_glossary id=\"1001\"]ash[\/pb_glossary] [pb_glossary id=\"1936\"]bed[\/pb_glossary] with radioisotopic dates of 54 million years and 50 million years, then geologists know the sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary] and its [pb_glossary id=\"1228\"]fossils[\/pb_glossary] formed between 54 and 50 million years ago. Another example would be a 65 million year old [pb_glossary id=\"228\"]volcanic[\/pb_glossary] [pb_glossary id=\"1021\"]dike[\/pb_glossary] that cut across sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary]. This provides an upper limit age on the sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary], so this [pb_glossary id=\"1935\"]strata[\/pb_glossary] would be older than 65 million years. Potassium is common in [pb_glossary id=\"1920\"]evaporite[\/pb_glossary] [pb_glossary id=\"1756\"]sediments[\/pb_glossary] and has been used for potassium\/argon dating<\/span><span style=\"font-weight: 400\">. Primary sedimentary [pb_glossary id=\"1765\"]minerals[\/pb_glossary] containing [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"1779\"]isotopes[\/pb_glossary] like <sup>40<\/sup>K, has provided dates for important geologic events.<\/span>\n<h3><span style=\"font-weight: 400\">7.2.5 Other Absolute Dating Techniques<\/span><\/h3>\n[caption id=\"attachment_3246\" align=\"alignright\" width=\"451\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Keizars_TLexplained2.jpg\"><img class=\"wp-image-493\" title=\"By Zkeizars (Own work) [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0-3.0-2.5-2.0-1.0&quot;>CC BY-SA 4.0-3.0-2.5-2.0-1.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AKeizars_TLexplained2.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Keizars_TLexplained2.jpg\" alt=\"The diagram explains the details of the technique, showing trapped electrons.\" width=\"451\" height=\"372\"><\/a> Thermoluminescence, a type of luminescence dating[\/caption]&nbsp;\n\n<span style=\"font-weight: 400\"><strong>Luminescence (aka Thermoluminescence):<\/strong> Radioisotopic dating is not the only way scientists determine numeric ages. Luminescence dating measures the time elapsed since some [pb_glossary id=\"1787\"]silicate[\/pb_glossary] [pb_glossary id=\"1765\"]minerals[\/pb_glossary], such as coarse-[pb_glossary id=\"1756\"]sediments[\/pb_glossary] of [pb_glossary id=\"1787\"]silicate[\/pb_glossary] [pb_glossary id=\"1765\"]minerals[\/pb_glossary], were last exposed to light or heat at the surface of Earth. All buried [pb_glossary id=\"1756\"]sediments[\/pb_glossary] are exposed to radiation from normal background radiation from the decay process described above. Some of these electrons get trapped in the crystal lattice of [pb_glossary id=\"1787\"]silicate[\/pb_glossary] [pb_glossary id=\"1765\"]minerals[\/pb_glossary] like [pb_glossary id=\"967\"]quartz[\/pb_glossary]. When exposed at the surface, ultraviolet radiation and heat from the Sun releases these electrons, but when the [pb_glossary id=\"1765\"]minerals[\/pb_glossary] are buried just a few inches below the surface, the electrons get trapped again. Samples of coarse [pb_glossary id=\"1756\"]sediments[\/pb_glossary] collected just a few feet below the surface are analyzed by stimulating them with light in a lab. This stimulation releases the trapped electrons as a photon of light which is called luminescence. The amount luminescence released indicates how long the [pb_glossary id=\"1756\"]sediment[\/pb_glossary] has been buried. Luminescence dating is only useful for dating young [pb_glossary id=\"1756\"]sediments[\/pb_glossary] that are less than 1 million years old. In Utah, luminescence dating is used to determine when coarse-grained [pb_glossary id=\"1756\"]sediment[\/pb_glossary] layers were buried near a [pb_glossary id=\"2143\"]fault[\/pb_glossary]. This is one technique used to determine the [pb_glossary id=\"2182\"]recurrence[\/pb_glossary] interval of large earthquakes on [pb_glossary id=\"2143\"]faults[\/pb_glossary] like the Wasatch [pb_glossary id=\"2143\"]Fault[\/pb_glossary] that primarily cut coarse-grained material and lack buried organic [pb_glossary id=\"250\"]soils[\/pb_glossary] for radiocarbon dating.<\/span>\n\n[caption id=\"attachment_3247\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Apatite-CaF-280343.jpg\"><img class=\"wp-image-494 size-medium\" title=\"Rob Lavinsky, <a rel=&quot;nofollow&quot; class=&quot;external text&quot; href=&quot;http:\/\/www.irocks.com\/&quot;>iRocks.com<\/a> \u2013 CC-BY-SA-3.0 [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AApatite-(CaF)-280343.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Apatite-CaF-280343-300x267.jpg\" alt=\"The crystal is hexagonal and light green.\" width=\"300\" height=\"267\"><\/a> Apatite from Mexico.[\/caption]<strong>Fission Track:<\/strong> Fission track dating relies on damage to the crystal lattice produced when unstable <sup>238<\/sup>U decays to the [pb_glossary id=\"1222\"]daughter product[\/pb_glossary] <sup>234<\/sup>Th and releases an alpha particle. These two decay products move in opposite directions from each other through the crystal lattice leaving a visible track of damage. This is common in uranium-bearing [pb_glossary id=\"1765\"]mineral[\/pb_glossary] grains such as apatite. The tracks are large and can be visually counted under an optical microscope. The number of tracks correspond to the age of the grains. Fission track dating works from about 100,000 to 2 billion (1 \u00d7 10<sup>5<\/sup> to 2 \u00d7 10<sup>9<\/sup>) years ago. Fission track dating has also been used as a second clock to confirm dates obtained by other methods.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"44\"]\n\n[caption id=\"attachment_4084\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/7.2-Did-I-Get-It-QR-Code.png\"><img class=\"wp-image-495 size-thumbnail\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 7.2 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">7.3 Fossils and Evolution<\/span><\/h2>\n[caption id=\"attachment_3248\" align=\"alignright\" width=\"222\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.3_Archaeopteryx_lithographica.jpg\"><img class=\"wp-image-496 size-medium\" title=\"By H. Raab (User: Vesta) (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a> or <a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AArchaeopteryx_lithographica_(Berlin_specimen).jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.3_Archaeopteryx_lithographica-222x300.jpg\" alt=\"Image of the Archaeopteryx fossil that show features of both reptiles and birds. This is a famous transition fossil between reptiles and birds.\" width=\"222\" height=\"300\"><\/a> Archaeopteryx lithographica, specimen displayed at the Museum f\u00fcr Naturkunde in Berlin.[\/caption]<span style=\"font-weight: 400\"><strong>[pb_glossary id=\"1228\"]Fossils[\/pb_glossary]<\/strong><\/span>\u00a0are any evidence of past life preserved in rocks. They may be actual remains of body parts (rare), impressions of soft body parts, [pb_glossary id=\"1231\"]casts[\/pb_glossary] and [pb_glossary id=\"1232\"]molds[\/pb_glossary] of body parts (more common), body parts replaced by [pb_glossary id=\"1765\"]mineral[\/pb_glossary] (common) or evidence of animal behavior such as footprints and burrows. The body parts of living organisms range from the hard bones and shells of animals, soft cellulose of plants, soft bodies of jellyfish, down to single cells of bacteria and algae. Which body parts can be preserved? The vast majority of life today consists soft-bodied and\/or single celled organisms, and will not likely be preserved in the geologic record except under unusual conditions. The best environment for preservation is the ocean, yet [pb_glossary id=\"1961\"]marine[\/pb_glossary] processes can [pb_glossary id=\"1893\"]dissolve[\/pb_glossary] hard parts and scavenging can reduce or eliminate remains. Thus, even under ideal conditions in the ocean, the likelihood of preservation is quite limited. For [pb_glossary id=\"1980\"]terrestrial[\/pb_glossary] life, the possibility of remains being buried and preserved is even more limited. In other words, the [pb_glossary id=\"1228\"]fossil[\/pb_glossary] record is incomplete and records only a small percentage of life that existed. Although incomplete, [pb_glossary id=\"1228\"]fossil[\/pb_glossary] records are used for [pb_glossary id=\"1237\"]stratigraphic correlation[\/pb_glossary], using the [pb_glossary id=\"2037\"]Principle of Faunal Succession[\/pb_glossary], and provide a method used for establishing the age of a [pb_glossary id=\"2038\"]formation[\/pb_glossary] on the Geologic Time Scale.\n<h3><span style=\"font-weight: 400\">7.3.1 Types of Preservation<\/span><\/h3>\n[caption id=\"attachment_3249\" align=\"alignleft\" width=\"148\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/ElrathiakingiUtahWheelerCambrian.jpg\"><img class=\"wp-image-497\" title=\"By Wilson44691 (Own work) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AElrathiakingiUtahWheelerCambrian.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/ElrathiakingiUtahWheelerCambrian-243x300.jpg\" alt=\"It has three lobes\" width=\"148\" height=\"183\"><\/a> Trilobites had a hard exoskeleton and are often preserved by permineralization.[\/caption]<span style=\"font-weight: 400\">Remnants or impressions of hard parts, such as a [pb_glossary id=\"1961\"]marine[\/pb_glossary] clam shell or dinosaur bone, are the most common types of [pb_glossary id=\"1228\"]fossils[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. <\/span>The original material has almost always been replaced with new [pb_glossary id=\"1765\"]minerals[\/pb_glossary] that preserve much of the shape of the original shell, bone, or cell. The common types of [pb_glossary id=\"1228\"]fossil[\/pb_glossary] preservation are [pb_glossary id=\"1229\"]actual preservation[\/pb_glossary], [pb_glossary id=\"1230\"]permineralization[\/pb_glossary], [pb_glossary id=\"1232\"]molds[\/pb_glossary] and [pb_glossary id=\"1231\"]casts[\/pb_glossary], [pb_glossary id=\"1234\"]carbonization[\/pb_glossary], and [pb_glossary id=\"1235\"]trace fossils[\/pb_glossary].\n\n<b>[pb_glossary id=\"1229\"]Actual preservation[\/pb_glossary] <\/b>is a rare form of fossilization where the original materials or hard parts of the organism are preserved. Preservation of soft-tissue is very rare since these organic materials easily disappear because of bacterial decay<span style=\"font-weight: 400\">.<\/span>\u00a0Examples of [pb_glossary id=\"1229\"]actual preservation[\/pb_glossary] are unaltered biological materials like insects in amber or original [pb_glossary id=\"1765\"]minerals[\/pb_glossary] like mother-of-pearl on the interior of a shell. Another example is mammoth skin and hair preserved in post-[pb_glossary id=\"1988\"]glacial[\/pb_glossary] deposits in the Arctic regions<span style=\"font-weight: 400\"><span style=\"font-weight: 400\">.\u00a0 Rare mummification has left fragments of soft tissue, skin, and sometimes even blood vessels of dinosaurs, from which proteins have been isolated and evidence for DNA fragments have been discovered.\u00a0<\/span><\/span>\n\n[caption id=\"attachment_3250\" align=\"aligncenter\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.19_mosquito_in_amber-scaled.jpg\"><img class=\"wp-image-3250 size-medium\" title=\"This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.19_mosquito_in_amber-scaled-1.jpg\" alt=\"Mosquito trapped in amber in actal preservation\" width=\"300\" height=\"206\"><\/a> Mosquito preserved in amber[\/caption]\n\n&nbsp;\n\n[caption id=\"attachment_3253\" align=\"aligncenter\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.20_Petrified_forest_log_2_md-1.jpg\"><img class=\"wp-image-357 size-medium\" title=\"By User:Moondigger (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/2.5&quot;>CC BY-SA 2.5<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3APetrified_forest_log_2_md.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.20_Petrified_forest_log_2_md-1-300x300.jpg\" alt=\"Photo of log of petrified wood showing structures of the original wood\" width=\"300\" height=\"300\"><\/a> Permineralization in petrified wood[\/caption]&nbsp;\n\n<strong>[pb_glossary id=\"1230\"]Permineralization[\/pb_glossary]<\/strong> occurs when an organism is buried, and then [pb_glossary id=\"1778\"]elements[\/pb_glossary] in [pb_glossary id=\"2207\"]groundwater[\/pb_glossary] completely impregnate all spaces within the body, even cells. Soft body structures can be preserved in great detail, but stronger materials like bone and teeth are the most likely to be preserved. Petrified wood is an example of detailed cellulose structures in the wood being preserved. The University of California Berkeley <a href=\"http:\/\/www.ucmp.berkeley.edu\/paleo\/fossils\/permin.html\">website<\/a> has more information on [pb_glossary id=\"1230\"]permineralization[\/pb_glossary].\n\n<strong>[pb_glossary id=\"1232\"]Molds[\/pb_glossary]<\/strong> and <strong>[pb_glossary id=\"1231\"]casts[\/pb_glossary]<\/strong> form when the original material of the organism dissolves and leaves a cavity in the surrounding rock. The shape of this cavity is an [pb_glossary id=\"1232\"]external mold[\/pb_glossary]. If the mold is subsequently filled with [pb_glossary id=\"1756\"]sediments[\/pb_glossary] or a [pb_glossary id=\"1765\"]mineral[\/pb_glossary] [pb_glossary id=\"1785\"]precipitate[\/pb_glossary], the organism\u2019s external shape is preserved as a [pb_glossary id=\"1231\"]cast[\/pb_glossary]. Sometimes internal cavities of organisms, such internal [pb_glossary id=\"1231\"]casts[\/pb_glossary] of clams, snails, and even skulls are preserved as internal [pb_glossary id=\"1231\"]casts[\/pb_glossary] showing details of soft structures. If the chemistry is right, and burial is rapid, [pb_glossary id=\"1765\"]mineral[\/pb_glossary] nodules form around soft structures preserving the three-dimensional detail. This is called <strong>[pb_glossary id=\"1233\"]authigenic mineralization[\/pb_glossary]<\/strong>.\n\n[caption id=\"attachment_3254\" align=\"aligncenter\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.21_external_mold_Aviculopecten_subcardiformis.jpg\"><img class=\"wp-image-499 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis-300x300.jpg\" alt=\"Photo of external mold of a clam shell\" width=\"300\" height=\"300\"><\/a> External mold of a clam[\/caption]\n\n[caption id=\"attachment_3255\" align=\"aligncenter\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.23_carbonization_of_ViburnumFossil.jpg\"><img class=\"wp-image-500 size-medium\" title=\"By Wilson44691 (Own work) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AViburnumFossil.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.23_carbonization_of_ViburnumFossil-300x215.jpg\" alt=\"carbonized leaf fossil showing insect damage and vein structure\" width=\"300\" height=\"215\"><\/a> Carbonized leaf[\/caption]&nbsp;\n\n<strong>[pb_glossary id=\"1234\"]Carbonization[\/pb_glossary]<\/strong> occurs when the organic tissues of an organism are compressed, the [pb_glossary id=\"1684\"]volatiles[\/pb_glossary] are driven out, and everything but the carbon disappears leaving a carbon silhouette of the original organism. Leaf and fern [pb_glossary id=\"1228\"]fossils[\/pb_glossary] are examples of [pb_glossary id=\"1234\"]carbonization[\/pb_glossary]<span style=\"font-weight: 400\">.<\/span>\n\n<strong>[pb_glossary id=\"1235\"]Trace fossils[\/pb_glossary]<\/strong> are indirect evidence left behind by an organism, such as burrows and footprints, as it lived its life. <strong>[pb_glossary id=\"1235\"]Ichnology[\/pb_glossary]<\/strong> is specifically the study of prehistoric animal tracks. Dinosaur tracks testify to their presence and movement over an area, and even provide information about their size, gait, speed, and behavior. Burrows dug by tunneling organisms tell of their presence and mode of life. <span style=\"font-weight: 400\">Other [pb_glossary id=\"1235\"]trace fossils[\/pb_glossary] include fossilized feces called <strong>coprolites<\/strong> and stomach stones called <strong>gastroliths<\/strong><\/span> that provide information about diet and habitat.\n\n&nbsp;\n\n[caption id=\"attachment_3256\" align=\"aligncenter\" width=\"189\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.24_Cheirotherium_prints_possibly_Ticinosuchus.jpg\"><img class=\"wp-image-501 size-medium\" title=\"<a href=&quot;https:\/\/en.wikipedia.org\/wiki\/User:Ballista&quot; class=&quot;extiw&quot; title=&quot;en:User:Ballista&quot;>Ballista<\/a> at the <a href=&quot;https:\/\/en.wikipedia.org\/wiki\/&quot; class=&quot;extiw&quot; title=&quot;w:&quot;>English language Wikipedia<\/a> [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ACheirotherium_prints_possibly_Ticinosuchus.JPG&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.24_Cheirotherium_prints_possibly_Ticinosuchus-189x300.jpg\" alt=\"Tracks of a smal1 dinosaur\" width=\"189\" height=\"300\"><\/a> Foot prints of the early crocodile Chirotherium[\/caption]\n\n[caption id=\"attachment_3257\" align=\"aligncenter\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.26_Coprolite.jpg\"><img class=\"wp-image-502 size-medium\" title=\"USGS, public domain\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.26_Coprolite-300x200.jpg\" alt=\"fossilized animal droppings\" width=\"300\" height=\"200\"><\/a> Fossil animal droppings (coprolite)[\/caption]\n\n&nbsp;\n<h3><span style=\"font-weight: 400\">7.3.2 Evolution<\/span><\/h3>\n<strong>Evolution<\/strong> has created a variety of ancient [pb_glossary id=\"1228\"]fossils[\/pb_glossary] that are important to [pb_glossary id=\"1237\"]stratigraphic correlation[\/pb_glossary]. (see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/7-geologic-time\/\">chapter 7<\/a> and <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">Chapter 5<\/a>) This section is a brief discussion of the process of evolution. The British naturalist Charles Darwin (1809-1882) recognized that life forms evolve into progeny life forms. He proposed <strong>natural selection<\/strong>\u2014which operated on organisms living under environmental conditions that posed challenges to survival\u2014was the mechanism driving the process of evolution forward.\n\n[caption id=\"attachment_3258\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.27_bell-shaped_curve.jpg\"><img class=\"wp-image-503 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.27_bell-shaped_curve-300x176.jpg\" alt=\"Berll-shaped curve showing how variation within a population is distributed with respect to characteristics. Most members group in the center with rarer members on the tails.\" width=\"300\" height=\"176\"><\/a> Variation within a population[\/caption]\n\n<span style=\"font-weight: 400\">The basic classification unit of life is the <strong>species<\/strong>: a population of organisms that exhibit shared characteristics and are capable of reproducing fertile offspring. For a species to survive, each individual within a particular population is faced with challenges posed by the environment and must survive them long enough to reproduce. Within the natural variations present in the population, there may be individuals possessing characteristics that give them some advantage in facing the environmental challenges. These individuals are more likely to reproduce and pass these favored characteristics on to successive generations. If sufficient individuals in a population fail to surmount the challenges of the environment and the population cannot produce enough viable offspring, the species becomes [pb_glossary id=\"755\"]extinct[\/pb_glossary]. The average lifespan of a species in the [pb_glossary id=\"1228\"]fossil[\/pb_glossary] record is around a million years. That life still exists on Earth shows the role and importance of evolution as a natural process in meeting the continual challenges posed by our dynamic Earth. If the inheritance of certain distinctive characteristics is sufficiently favored over time, populations may become genetically isolated from one another, eventually resulting in the evolution of separate species. This genetic isolation may also be caused by a geographic barrier, such as an island surrounded by ocean. This [pb_glossary id=\"1733\"]theory[\/pb_glossary] of evolution by natural selection was elaborated by Darwin in his book <em>On the Origin of Species<\/em>\u00a0(see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/1-understanding-science\/\">Chapter 1<\/a>). <\/span>Since Darwin\u2019s original ideas, technology has provided many tools and mechanisms to study how evolution and speciation take place and this arsenal of tools is growing. Evolution is well beyond the [pb_glossary id=\"1730\"]hypothesis[\/pb_glossary] stage and is a well-established [pb_glossary id=\"1733\"]theory[\/pb_glossary] of modern science.\n\nVariation within populations occurs by the natural mixing of genes through sexual reproduction or from naturally occurring mutations. Some of this genetic variation can introduce advantageous characteristics that increase the individual\u2019s chances of survival. While some species in the [pb_glossary id=\"1228\"]fossil[\/pb_glossary] record show little morphological change over time, others show gradual or punctuated changes, within which [pb_glossary id=\"1007\"]intermediate[\/pb_glossary] forms can be seen.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"45\"]\n\n[caption id=\"attachment_4085\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/7.3-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-504\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 7.3 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\"> 7.4 Correlation<\/span><\/h2>\n[caption id=\"attachment_3259\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Wegener_fossil_map.svg_.png\"><img class=\"wp-image-71 size-medium\" title=\"By Osvaldocangaspadilla (Own work) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ASnider-Pellegrini_Wegener_fossil_map.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Wegener_fossil_map.svg_-300x231.png\" alt=\"There are four different fossil organisms that connect South America, Africa, India, Antartica, and Australia.\" width=\"300\" height=\"231\"><\/a> Image showing fossils that connect the continents of Gondwana (the southern continents of Pangea).[\/caption][pb_glossary id=\"1236\"]Correlation[\/pb_glossary] is the process of establishing which sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary] are of the same age but geographically separate. [pb_glossary id=\"1236\"]Correlation[\/pb_glossary] can be determined by using magnetic polarity reversals (<a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>), rock types, unique rock sequences, or [pb_glossary id=\"1241\"]index fossils[\/pb_glossary]. There are four main types of [pb_glossary id=\"1236\"]correlation[\/pb_glossary]: [pb_glossary id=\"1937\"]stratigraphic[\/pb_glossary], lithostratigraphic, chronostratigraphic, and biostratigraphic.\n<h3><strong>7.4.1 Stratigraphic Correlation<\/strong><\/h3>\n<strong>[pb_glossary id=\"1237\"]Stratigraphic correlation[\/pb_glossary]<\/strong> is the process of establishing which sedimentary [pb_glossary id=\"1935\"]strata[\/pb_glossary] are the same age at distant geographical areas by means of their [pb_glossary id=\"1937\"]stratigraphic[\/pb_glossary] relationship. Geologists construct geologic histories of areas by mapping and making [pb_glossary id=\"1937\"]stratigraphic[\/pb_glossary] columns-a detailed description of the [pb_glossary id=\"1935\"]strata[\/pb_glossary] from bottom to top. An example of [pb_glossary id=\"1937\"]stratigraphic[\/pb_glossary] relationships and [pb_glossary id=\"1236\"]correlation[\/pb_glossary] between Canyonlands National Park and Zion National Park in Utah. At Canyonlands, the Navajo [pb_glossary id=\"1912\"]Sandstone[\/pb_glossary] overlies the Kayenta [pb_glossary id=\"2038\"]Formation[\/pb_glossary] which overlies the cliff-forming Wingate [pb_glossary id=\"2038\"]Formation[\/pb_glossary]. In Zion, the Navajo [pb_glossary id=\"1912\"]Sandstone[\/pb_glossary] overlies the Kayenta [pb_glossary id=\"2038\"]formation[\/pb_glossary] which overlies the cliff-forming Moenave [pb_glossary id=\"2038\"]Formation[\/pb_glossary]. Based on the [pb_glossary id=\"1937\"]stratigraphic[\/pb_glossary] relationship, the Wingate and Moenave [pb_glossary id=\"2038\"]Formations[\/pb_glossary] correlate. These two [pb_glossary id=\"2038\"]formations[\/pb_glossary] have unique names because their [pb_glossary id=\"1909\"]composition[\/pb_glossary] and outcrop pattern is slightly different.<span style=\"font-weight: 400\"> Other [pb_glossary id=\"1935\"]strata[\/pb_glossary] in the Colorado Plateau and their sequence can be recognized and correlated over thousands of square miles.<\/span>\n\n[caption id=\"attachment_3260\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.4_Grand_Staircase_Correlation.jpg\"><img class=\"wp-image-505 size-large\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation-1024x291.jpg\" alt=\"Cross-section showing the same strata in the Grand Canyon, Zion, Bryce Canyon, and Cedar Breaks\" width=\"1024\" height=\"291\"><\/a> Correlation of strata along the Grand Staircase from the Grand Canyon to Zion Canyon, Bryce Canyon and Cedar Breaks. (Source: National Park Service)[\/caption]\n<h3><strong>7.4.2 Lithostratigraphic Correlation<\/strong><\/h3>\n[caption id=\"attachment_3261\" align=\"alignright\" width=\"221\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.28_Navajo_Sandstone_Zion_angels_landing_view.jpg\"><img class=\"wp-image-506\" title=\"By Diliff (taken by Diliff) [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a>, <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/2.5-2.0-1.0&quot;>CC BY-SA 2.5-2.0-1.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AZion_angels_landing_view.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.28_Navajo_Sandstone_Zion_angels_landing_view-293x300.jpg\" alt=\"View of Navajo Sandstone from Angel's Landing in Zion National Park\" width=\"221\" height=\"227\"><\/a> View of Navajo Sandstone from Angel's Landing in Zion's National Park[\/caption]<strong>[pb_glossary id=\"1238\"]Lithostratigraphic correlation[\/pb_glossary]<\/strong> establishes a similar age of [pb_glossary id=\"1935\"]strata[\/pb_glossary] based on the <strong>lithology<\/strong> that is the [pb_glossary id=\"1909\"]composition[\/pb_glossary] and physical properties of that [pb_glossary id=\"1935\"]strata[\/pb_glossary].<em> Lithos<\/em> is Greek for stone and -logy comes from the Greek word for doctrine or science.\u00a0 [pb_glossary id=\"1238\"]Lithostratigraphic correlation[\/pb_glossary] can be used to correlate whole [pb_glossary id=\"2038\"]formations[\/pb_glossary] long distances or can be used to correlate smaller [pb_glossary id=\"1935\"]strata[\/pb_glossary] within formations to trace their extent and regional [pb_glossary id=\"1960\"]depositional environments[\/pb_glossary].\n\n[caption id=\"attachment_3262\" align=\"alignleft\" width=\"232\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.29_Navajo_Sandstone_StevensArchUT.jpg\"><img class=\"wp-image-507\" title=\"By G. Thomas at English Wikipedia [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AStevensArchUT.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.29_Navajo_Sandstone_StevensArchUT-300x212.jpg\" alt=\"Stevens Arch in the Navajo Sandstone at Coyote Gulch some 125 miles away from Zions Park\" width=\"232\" height=\"164\"><\/a> Stevens Arch in the Navajo Sandstone at Coyote Gulch some 125 miles away from Zions Park[\/caption]For example, the Navajo [pb_glossary id=\"1912\"]Sandstone[\/pb_glossary], which makes up the prominent walls of Zion National Park, is the same Navajo [pb_glossary id=\"1912\"]Sandstone[\/pb_glossary] in Canyonlands because the lithology of the two are identical even though they are hundreds of miles apart. \u00a0Extensions of the same Navajo [pb_glossary id=\"1912\"]Sandstone[\/pb_glossary] [pb_glossary id=\"2038\"]formation[\/pb_glossary] are found miles away in other parts of southern Utah, including Capitol [pb_glossary id=\"1976\"]Reef[\/pb_glossary] and Arches National Parks. Further, this same [pb_glossary id=\"2038\"]formation[\/pb_glossary] is the called the Aztec [pb_glossary id=\"1912\"]Sandstone[\/pb_glossary] in Nevada and Nugget [pb_glossary id=\"1912\"]Sandstone[\/pb_glossary] near Salt Lake City because they are lithologically distinct enough to warrant new names.\n<h3><strong>7.4.3 Chronostratigraphic Correlation<\/strong><\/h3>\n<strong>[pb_glossary id=\"1239\"]Chronostratigraphic correlation[\/pb_glossary]<\/strong> matches rocks of the same age, even though they are made of different lithologies. Different lithologies of sedimentary rocks can form at the same time at different geographic locations because [pb_glossary id=\"1960\"]depositional environments[\/pb_glossary] vary geographically. For example, at any one time in a [pb_glossary id=\"1961\"]marine[\/pb_glossary] setting there could be this sequence of [pb_glossary id=\"1960\"]depositional environments[\/pb_glossary] from beach to deep [pb_glossary id=\"1961\"]marine[\/pb_glossary]: beach, near [pb_glossary id=\"2273\"]shore[\/pb_glossary] area, shallow [pb_glossary id=\"1961\"]marine[\/pb_glossary] [pb_glossary id=\"1978\"]lagoon[\/pb_glossary], [pb_glossary id=\"1976\"]reef[\/pb_glossary], slope, and deep [pb_glossary id=\"1961\"]marine[\/pb_glossary]. Each [pb_glossary id=\"1960\"]depositional environment[\/pb_glossary] will have a unique [pb_glossary id=\"1761\"]sedimentary rock[\/pb_glossary] [pb_glossary id=\"2038\"]formation[\/pb_glossary]. On the figure of the [pb_glossary id=\"476\"]Permian[\/pb_glossary] Capitan [pb_glossary id=\"1976\"]Reef[\/pb_glossary] at Guadalupe National Monument in West Texas, the red line shows a chronostratigraphic time line that represents a snapshot in time. Shallow-water [pb_glossary id=\"1961\"]marine[\/pb_glossary] [pb_glossary id=\"1978\"]lagoon[\/pb_glossary]\/back [pb_glossary id=\"1976\"]reef[\/pb_glossary] area is light blue, the main Capitan [pb_glossary id=\"1976\"]reef[\/pb_glossary] is dark blue, and deep-water [pb_glossary id=\"1961\"]marine[\/pb_glossary] [pb_glossary id=\"1918\"]siltstone[\/pb_glossary] is yellow. All three of these unique lithologies were forming at the same time in [pb_glossary id=\"476\"]Permian[\/pb_glossary] along this red timeline.\n\n&nbsp;\n\n[caption id=\"attachment_3263\" align=\"aligncenter\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.4_Chronostrat_Guadelupe_NM.png\"><img class=\"wp-image-508 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Chronostrat_Guadelupe_NM-300x184.png\" alt=\"Cross-section showing three different rocks strata with unique lithology all being deposited at the same ancient time in nearby geographic areas.\" width=\"300\" height=\"184\"><\/a> Cross-section of the Permian El Capitan Reef at Guadalupe National Monument, Texas. The red line shows a chronostratigraphic time line that represents a snapshot in time in which the shallow marine lagoon\/back reef area (light blue), main Capitan reef (dark blue), and deep marine silstones (yellow) were all being deposited at the same time.[\/caption]\n\n[caption id=\"attachment_3264\" align=\"aligncenter\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/TransgressionRegression-1.png\"><img class=\"wp-image-410 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/TransgressionRegression-1-300x199.png\" alt=\"Onlap is sediments moving toward the land. Offlap is moving away.\" width=\"300\" height=\"199\"><\/a> The rising sea levels of transgressions create onlapping sediments, regressions create offlapping. Ocean water is shown in blue so the time line is on the surface below the water. At the same time sandstone (buff color), limestone (gray), and shale (mustard color) are all forming at different depths of water.[\/caption]\n<h3><strong>7.4.4 Biostratigraphic Correlation<\/strong><\/h3>\n[caption id=\"attachment_3265\" align=\"alignright\" width=\"250\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.32_Conodonts_from_Alaska.jpg\"><img class=\"wp-image-509 size-medium\" title=\"USGS image, public domain\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.32_Conodonts_from_Alaska-250x300.jpg\" alt=\"Illustration of microscopic conodonts from Alaska showing several different plate and tooth-like forms\" width=\"250\" height=\"300\"><\/a> Conodonts[\/caption]\n\n<strong>[pb_glossary id=\"1240\"]Biostratigraphic correlation[\/pb_glossary]<\/strong> uses [pb_glossary id=\"1241\"]index fossils[\/pb_glossary] to determine [pb_glossary id=\"1935\"]strata[\/pb_glossary] ages. [pb_glossary id=\"1241\"]Index fossils[\/pb_glossary] represent assemblages or groups of organisms that were uniquely present during specific intervals of geologic time. Assemblages is referring a group of [pb_glossary id=\"1228\"]fossils[\/pb_glossary]. [pb_glossary id=\"1228\"]Fossils[\/pb_glossary] allow geologists to assign a [pb_glossary id=\"2038\"]formation[\/pb_glossary] to an absolute date range, such as the [pb_glossary id=\"486\"]Jurassic[\/pb_glossary] [pb_glossary id=\"1244\"]Period[\/pb_glossary] (199 to 145 million years ago), rather than a relative time scale. In fact, most of the geologic time ranges are mapped to [pb_glossary id=\"1228\"]fossil[\/pb_glossary] assemblages. The most useful [pb_glossary id=\"1241\"]index fossils[\/pb_glossary] come from lifeforms that were geographically widespread and had a species lifespan that was limited to a narrow time interval. In other words, [pb_glossary id=\"1241\"]index fossils[\/pb_glossary]\u00a0can be found in many places around the world, but only during a narrow time frame. Some of the best [pb_glossary id=\"1228\"]fossils[\/pb_glossary] for [pb_glossary id=\"1240\"]biostratigraphic correlation[\/pb_glossary] are microfossils<strong>,<\/strong> most of which came from single-celled organisms. As with microscopic organisms today, they were widely distributed across many environments throughout the world. Some of these microscopic organisms had hard parts, such as exoskeletons or outer shells, making them better candidates for preservation. Foraminifera, single celled organisms with calcareous shells, are an example of an especially useful [pb_glossary id=\"1241\"]index fossil[\/pb_glossary] for the [pb_glossary id=\"487\"]Cretaceous[\/pb_glossary] [pb_glossary id=\"1244\"]Period[\/pb_glossary] and [pb_glossary id=\"488\"]Cenozoic[\/pb_glossary] [pb_glossary id=\"1243\"]Era[\/pb_glossary]<span style=\"font-weight: 400\">.<\/span>\n\n<strong>Conodonts<\/strong> are another example of microfossils useful for [pb_glossary id=\"1240\"]biostratigraphic correlation[\/pb_glossary] of the [pb_glossary id=\"1276\"]Cambrian[\/pb_glossary] through [pb_glossary id=\"485\"]Triassic[\/pb_glossary] [pb_glossary id=\"1244\"]Periods[\/pb_glossary]. Conodonts are tooth-like phosphatic structures of an eel-like multi-celled organism that had no other preservable hard parts. The conodont-bearing creatures lived in shallow [pb_glossary id=\"1961\"]marine[\/pb_glossary] environments all over the world. Upon death, the phosphatic hard parts were scattered into the rest of the [pb_glossary id=\"1961\"]marine[\/pb_glossary] [pb_glossary id=\"1756\"]sediments[\/pb_glossary]. These distinctive tooth-like structures are easily collected and separated from [pb_glossary id=\"1929\"]limestone[\/pb_glossary] in the laboratory.\n\n[caption id=\"attachment_3266\" align=\"aligncenter\" width=\"380\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.21_index_fossils.gif\"><img class=\"wp-image-510\" title=\"USGS image\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_index_fossils-300x237.gif\" alt=\"Image showing index fossils that identify ages of the Geologic Time Scale\" width=\"380\" height=\"300\"><\/a> Index fossils used for biostratigraphic correlation[\/caption]\n\n&nbsp;\n\n[caption id=\"attachment_3267\" align=\"aligncenter\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.31_foraminifera_Quinqueloculina_seminula-scaled.jpg\"><img class=\"wp-image-3267 size-medium\" title=\"\u00a9 Hans Hillewaert&amp;nbsp;\/&amp;nbsp;, <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AQuinqueloculina_seminula.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.31_foraminifera_Quinqueloculina_seminula-scaled-1.jpg\" alt=\"Specimens of faraminifera, a microfossil with a hard shell\" width=\"300\" height=\"225\"><\/a> Foraminifera, microscopic creatures with hard shells[\/caption]\n\n[caption id=\"attachment_3268\" align=\"alignleft\" width=\"299\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.33_Euconodonta.gif\"><img class=\"wp-image-512 size-full\" title=\"By Philippe Janvier, 1997 (Tree of Life Web Project) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by\/3.0&quot;>CC BY 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AEuconodonta.gif&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Euconodonta.gif\" alt=\"Artists rendering of what the conodont anmal might have looked like, an eel-like creature with large eyes and an apparatus of conodonts as mouthparts.\" width=\"299\" height=\"234\"><\/a> Artist reconstruction of the conodont animal[\/caption]&nbsp;\n\n<span style=\"font-weight: 400\">Because the conodont creatures were so widely abundant, rapidly evolving, and readily preserved in [pb_glossary id=\"1756\"]sediments[\/pb_glossary], their [pb_glossary id=\"1228\"]fossils[\/pb_glossary] are especially useful for correlating [pb_glossary id=\"1935\"]strata[\/pb_glossary], even though knowledge of the actual animal possessing them is sparse. Scientists in the 1960s carried out a fundamental [pb_glossary id=\"1240\"]biostratigraphic correlation[\/pb_glossary] that tied [pb_glossary id=\"485\"]Triassic[\/pb_glossary] conodont zonation into ammonoids, which are [pb_glossary id=\"755\"]extinct[\/pb_glossary] ancient cousins of the pearly nautilus. Up to that point ammonoids were the only standard for [pb_glossary id=\"485\"]Triassic[\/pb_glossary] [pb_glossary id=\"1236\"]correlation[\/pb_glossary], so cross-referencing micro- and macro-[pb_glossary id=\"1241\"]index fossils[\/pb_glossary] enhanced the reliability of [pb_glossary id=\"1240\"]biostratigraphic correlation[\/pb_glossary] for either type<\/span><span style=\"font-weight: 400\">. <\/span>That conodont study went on to establish the use of conodonts to internationally correlate [pb_glossary id=\"485\"]Triassic[\/pb_glossary] [pb_glossary id=\"1935\"]strata[\/pb_glossary] located in Europe, Western North America, and the Arctic Islands of Canada<span style=\"font-weight: 400\">.\u00a0<\/span>\n<h3><span style=\"font-weight: 400\">7.4.5 Geologic Time Scale<\/span><\/h3>\n[caption id=\"attachment_2486\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/GeologicClock.png\"><img class=\"wp-image-52 size-medium\" title=\"<code>By WoudloperDerivative work: Hardwigg (File:Geologic_clock.jpg) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AGeologic_Clock_with_events_and_periods.svg&quot;>via Wikimedia Commons<\/a><\/code>\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/GeologicClock-300x288.png\" alt=\"The circle starts at 4.6 billion years ago, then loops around to zero.\" width=\"300\" height=\"288\"><\/a> Geologic time on Earth, represented circularly, to show the individual time divisions and important events. Ga=billion years ago, Ma=million years ago.[\/caption]&nbsp;\n\nGeologic time has been subdivided into a series of divisions by geologists. [pb_glossary id=\"1242\"]Eon[\/pb_glossary] is the largest division of time, followed by [pb_glossary id=\"1243\"]era[\/pb_glossary], [pb_glossary id=\"1244\"]period[\/pb_glossary], [pb_glossary id=\"1245\"]epoch[\/pb_glossary], and age. The partitions of the geologic time scale is the same everywhere on Earth; however, rocks may or may not be present at a given location depending on the geologic activity going on during a particular [pb_glossary id=\"1244\"]period[\/pb_glossary] of time. Thus, we have the concept of time vs. rock, in which time is an unbroken continuum but rocks may be missing and\/or unavailable for study. The figure of the geologic time scale, represents time flowing continuously from the beginning of the Earth, with the time units presented in an unbroken sequence. But that does not mean there are rocks available for study for all of these time units.\n\n&nbsp;\n\n[caption id=\"attachment_2487\" align=\"aligncenter\" width=\"793\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/17.18_Geologic_Time_Scale_with_years-1.jpg\"><img class=\"wp-image-53 size-large\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/17.18_Geologic_Time_Scale_with_years-1-793x1024.jpg\" alt=\"The Geologic Time Scale with an age of each unit shown by a scale\" width=\"793\" height=\"1024\"><\/a> Geologic Time Scale with ages shown[\/caption]\n\n[caption id=\"attachment_3271\" align=\"alignright\" width=\"207\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.33_Geologic_time_scale_of_earth.jpg\"><img class=\"wp-image-513\" title=\"1888-1889, Popular Science Monthly Volume 34 (public domain)\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-373x1024.jpg\" alt=\"Stylized column of rock strata related to the eras and periods of the Geologic Time Scale illustrating the association of time, rock, and earth history\" width=\"207\" height=\"568\"><\/a> Names from the Geologic Time Scale applied to strata in a region[\/caption]\n\nThe geologic time scale was developed during the 19<sup>th<\/sup> century using the principles of [pb_glossary id=\"1937\"]stratigraphy[\/pb_glossary]. The relative order of the time units was determined before geologist had the tools to assign numerical ages to [pb_glossary id=\"1244\"]periods[\/pb_glossary] and events. [pb_glossary id=\"1240\"]Biostratigraphic correlation[\/pb_glossary] using [pb_glossary id=\"1228\"]fossils[\/pb_glossary] to assign [pb_glossary id=\"1243\"]era[\/pb_glossary] and [pb_glossary id=\"1244\"]period[\/pb_glossary] names to sedimentary rocks on a worldwide scale<span style=\"font-weight: 400\">. <\/span><span style=\"font-weight: 400\">With the expansion of science and technology, some geologists think the influence of humanity on natural processes has become so great they are suggesting a new geologic time [pb_glossary id=\"1244\"]period[\/pb_glossary], known as the <strong>[pb_glossary id=\"489\"]Anthropocene[\/pb_glossary]<\/strong>.<\/span><span style=\"font-weight: 400\">\n<\/span>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"46\"]\n\n[caption id=\"attachment_4086\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/7.4-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-514\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 7.4 via this QR Code.[\/caption]\n<h2>Chapter summary<\/h2>\nEvents in Earth history can be placed in sequence using the five principles of [pb_glossary id=\"2031\"]relative dating[\/pb_glossary]. The geologic time scale was completely worked out in the 19th Century using these principles without knowing any actual numeric ages for the events. The discovery of [pb_glossary id=\"2044\"]radioactivity[\/pb_glossary] in the late 1800s enabled [pb_glossary id=\"2043\"]absolute dating[\/pb_glossary], the assignment of numerical ages to events in the Earth\u2019s history, using decay of unstable [pb_glossary id=\"2044\"]radioactive[\/pb_glossary] [pb_glossary id=\"1779\"]isotopes[\/pb_glossary]. Accurately interpreting radioisotopic dating data depends on the type of rock tested and accurate assumptions about [pb_glossary id=\"1779\"]isotope[\/pb_glossary] baseline values. With a combination of relative and [pb_glossary id=\"2043\"]absolute dating[\/pb_glossary], the history of geological events, age of Earth, and a geologic time scale have been determined with considerable accuracy. [pb_glossary id=\"1237\"]Stratigraphic correlation[\/pb_glossary] is additional tool used for understanding how [pb_glossary id=\"1960\"]depositional environments[\/pb_glossary] change geographically. Geologic time is vast, providing plenty of time for the evolution of various lifeforms, and some of these have become preserved as [pb_glossary id=\"1228\"]fossils[\/pb_glossary] that can be used for [pb_glossary id=\"1240\"]biostratigraphic correlation[\/pb_glossary]. The geologic time scale is continuous, although the rock record may be broken because rocks representing certain time [pb_glossary id=\"1244\"]periods[\/pb_glossary] may be missing.\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n[h5p id=\"47\"]\n\n[caption id=\"attachment_4087\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Ch.-7-Review-QR-Code.png\"><img class=\"size-thumbnail wp-image-515\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the review quiz for Chapter 7 via this QR Code.[\/caption]\n<h1><span style=\"font-weight: 400\">References<\/span><\/h1>\n<div class=\"csl-bib-body\">\n<ol>\n \t<li class=\"csl-entry\">Allison, P.A., and Briggs, D.E.G., 1993, Exceptional [pb_glossary id=\"1228\"]fossil[\/pb_glossary] record: Distribution of soft-tissue preservation through the [pb_glossary id=\"1269\"]Phanerozoic[\/pb_glossary]: Geology, v. 21, no. 6, p. 527\u2013530.<\/li>\n \t<li class=\"csl-entry\">Bell, E.A., Boehnke, P., Harrison, T.M., and Mao, W.L., 2015, Potentially biogenic carbon preserved in a 4.1 billion-year-old [pb_glossary id=\"1227\"]zircon[\/pb_glossary]: Proc. Natl. Acad. Sci. U. S. A., v. 112, no. 47, p. 14518\u201314521.<\/li>\n \t<li class=\"csl-entry\">Brent Dalrymple, G., 1994, The Age of the Earth: Stanford University Press.<\/li>\n \t<li class=\"csl-entry\">Burleigh, R., 1981, W. F. Libby and the development of radiocarbon dating: Antiquity, v. 55, no. 214, p. 96\u201398.<\/li>\n \t<li class=\"csl-entry\">Christopher B. DuRoss, Stephen F. Personius, Anthony J. Crone, Susan S. Olig, and William R. Lund, 2011, Integration of Paleoseismic Data from Multiple Sites to Develop an [pb_glossary id=\"1722\"]Objective[\/pb_glossary] Earthquake Chronology: Application to the Weber Segment of the Wasatch [pb_glossary id=\"2143\"]Fault[\/pb_glossary] Zone, Utah: Bulletin of the Seismological Society of America, v. 101, no. 6, p. 2765\u20132781., doi: <a href=\"https:\/\/doi.org\/0.1785\/0120110102\">0.1785\/0120110102<\/a>.<\/li>\n \t<li class=\"csl-entry\">Dass, C., 2007, Basics of mass spectrometry, <i>in<\/i> Fundamentals of Contemporary Mass Spectrometry: John Wiley &amp; Sons, Inc., p. 1\u201314.<\/li>\n \t<li class=\"csl-entry\">Elston, D.P., Billingsley, G.H., and Young, R.A., 1989, Geology of Grand Canyon, Northern Arizona (with Colorado [pb_glossary id=\"2212\"]River[\/pb_glossary] Guides): Lees Ferry to Pierce Ferry, Arizona: Amer Geophysical Union.<\/li>\n \t<li class=\"csl-entry\">Erickson, J., Coates, D.R., and Erickson, H.P., 2014, An introduction to [pb_glossary id=\"1228\"]fossils[\/pb_glossary] and [pb_glossary id=\"1765\"]minerals[\/pb_glossary]: seeking clues to the Earth\u2019s past: Facts on File science library, Facts On File, Incorporated, Facts on File science library.<\/li>\n \t<li class=\"csl-entry\">Geyh, M.A., and Schleicher, H., 1990, Absolute Age Determination: Physical and Chemical Dating Methods and Their Application, 503 pp: [pb_glossary id=\"2252\"]Spring[\/pb_glossary]-er-Verlag, New York.<\/li>\n \t<li class=\"csl-entry\">Ireland, T., 1999, New tools for isotopic analysis: Science, v. 286, no. 5448, p. 2289\u20132290.<\/li>\n \t<li class=\"csl-entry\">Jackson, P.W., and of London, G.S., 2007, Four Centuries of Geological Travel: The Search for Knowledge on Foot, Bicycle, Sledge and Camel: Geological Society special publication, Geological Society, Geological Society special publication.<\/li>\n \t<li class=\"csl-entry\">Jaffey, A.H., Flynn, K.F., Glendenin, L.E., Bentley, W.C., and others, 1971, Precision measurement of half-lives and specific activities of U 235 and U 238: Phys. Rev. C Nucl. Phys.<\/li>\n \t<li class=\"csl-entry\">L\u00e9ost, I., F\u00e9raud, G., Blanc-Valleron, M.M., and Rouchy, J.M., 2001, First [pb_glossary id=\"2043\"]absolute dating[\/pb_glossary] of Miocene Langbeinite [pb_glossary id=\"1920\"]evaporites[\/pb_glossary] by 40Ar\/39Ar laser step-heating:[K2Mg2 (SO4) 3] Stebnyk [pb_glossary id=\"2402\"]Mine[\/pb_glossary] (Carpathian Foredeep [pb_glossary id=\"508\"]Basin[\/pb_glossary]): Geophys. Res. Lett., v. 28, no. 23, p. 4347\u20134350.<\/li>\n \t<li class=\"csl-entry\">Mosher, L.C., 1968, [pb_glossary id=\"485\"]Triassic[\/pb_glossary] conodonts from Western North America and Europe and Their [pb_glossary id=\"1236\"]Correlation[\/pb_glossary]: J. Paleontol., v. 42, no. 4, p. 895\u2013946.<\/li>\n \t<li class=\"csl-entry\">Oberth\u00fcr, T., Davis, D.W., Blenkinsop, T.G., and H\u00f6hndorf, A., 2002, Precise U\u2013Pb [pb_glossary id=\"1765\"]mineral[\/pb_glossary] ages, Rb\u2013Sr and Sm\u2013Nd systematics for the Great Dyke, Zimbabwe\u2014constraints on late [pb_glossary id=\"1257\"]Archean[\/pb_glossary] events in the Zimbabwe [pb_glossary id=\"1718\"]craton[\/pb_glossary] and Limpopo belt: [pb_glossary id=\"1270\"]Precambrian[\/pb_glossary] Res., v. 113, no. 3\u20134, p. 293\u2013305.<\/li>\n \t<li class=\"csl-entry\">Patterson, C., 1956, Age of [pb_glossary id=\"1254\"]meteorites[\/pb_glossary] and the earth: Geochim. Cosmochim. Acta, v. 10, no. 4, p. 230\u2013237.<\/li>\n \t<li class=\"csl-entry\">Schweitzer, M.H., Wittmeyer, J.L., Horner, J.R., and Toporski, J.K., 2005, Soft-tissue vessels and cellular preservation in Tyrannosaurus rex: Science, v. 307, no. 5717, p. 1952\u20131955.<\/li>\n \t<li class=\"csl-entry\">Valley, J.W., Peck, W.H., King, E.M., and Wilde, S.A., 2002, A cool early Earth: Geology, v. 30, no. 4, p. 351\u2013354.<\/li>\n \t<li class=\"csl-entry\">Whewell, W., 1837, History of the Inductive Sciences: From the Earliest to the Present Times: J.W. Parker, 492 p.<\/li>\n \t<li class=\"csl-entry\">Wilde, S.A., Valley, J.W., Peck, W.H., and Graham, C.M., 2001, Evidence from [pb_glossary id=\"2441\"]detrital[\/pb_glossary] [pb_glossary id=\"1227\"]zircons[\/pb_glossary] for the existence of continental crust and oceans on the Earth 4.4 Gyr ago: Nature, v. 409, no. 6817, p. 175\u2013178.<\/li>\n \t<li class=\"csl-entry\">Winchester, S., 2009, The Map That Changed the World: William Smith and the Birth of Modern Geology: HarperCollins.<\/li>\n<\/ol>\n<\/div>\n<span style=\"font-weight: 400\">\u00a0<\/span>","rendered":"<figure id=\"attachment_3216\" aria-describedby=\"caption-attachment-3216\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Grand_Canyon_Beauty-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-large wp-image-3216\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2021\/12\/Grand_Canyon_Beauty-scaled-1.jpg\" alt=\"The canyon is shown with many layers\" width=\"1024\" height=\"683\" \/><\/a><figcaption id=\"caption-attachment-3216\" class=\"wp-caption-text\">Perhaps no place on Earth better exemplifies the principles geologists use to determine the ages of rocks than Arizona\u2019s Grand Canyon National Park.<\/figcaption><\/figure>\n<p><b>KEY CONCEPTS<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Explain the difference between relative time and numeric time<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Describe the five principles of stratigraphy<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Apply relative dating principles to a block diagram and interpret the sequence of geologic events<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Define an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a>, and explain alpha decay, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1223\">beta decay<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1225\">electron capture<\/a> as mechanisms of radioactive decay<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Describe how radioisotopic dating is accomplished and list the four key <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a>\u00a0used<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Explain how carbon-14 forms in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1745\">atmosphere<\/a> and how it is used in dating recent events<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Explain how scientists know the numeric age of <\/span><span style=\"font-weight: 400\">the Earth and other events in Earth history<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Explain how sedimentary sequences can be dated using radioisotopes and other techniques<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Define a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossil<\/a> and describe types of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> preservation<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Outline how natural selection takes place as a mechanism of evolution<\/span><\/li>\n<li style=\"font-weight: 400\">Describe <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1237\">stratigraphic correlation<\/a><\/li>\n<li style=\"font-weight: 400\">List the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1242\">eons<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1243\">eras<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">periods<\/a> of the geologic time scale and explain the purpose behind the divisions<\/li>\n<li>Explain the relationship between time units and corresponding rock units\u2014<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1239\">chronostratigraphy<\/a> versus <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1238\">lithostratigraphy<\/a><\/li>\n<\/ul>\n<figure id=\"attachment_3217\" aria-describedby=\"caption-attachment-3217\" style=\"width: 225px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Portrait_of_Nicolas_Stenonus.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-464 size-full\" title=\"Unsigned but attributed to court painter Justus Sustermans\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Portrait_of_Nicolas_Stenonus.jpg\" alt=\"It shows a man\" width=\"225\" height=\"300\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Portrait_of_Nicolas_Stenonus.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Portrait_of_Nicolas_Stenonus-65x87.jpg 65w\" sizes=\"auto, (max-width: 225px) 100vw, 225px\" \/><\/a><figcaption id=\"caption-attachment-3217\" class=\"wp-caption-text\">Nicolas Steno, c. 1670<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The geologic time scale and basic outline of Earth\u2019s history were worked out long before we had any scientific means of assigning numerical age units, like years, to events of Earth history. Working out Earth\u2019s history depended on realizing some key principles of relative time. Nicolas Steno (1638-1686) introduced basic principles of stratigraphy, the study of layered rocks, in 1669<\/span><span style=\"font-weight: 400\">. William Smith (1769-1839), working with the strata of English coal mines, noticed that strata and their sequence were consistent throughout the region. Eventually he produced the first national geologic map of Britain<\/span><span style=\"font-weight: 400\">,<\/span><span style=\"font-weight: 400\"> becoming known as \u201cthe Father of English Geology.\u201d Nineteenth-century scientists developed a relative time scale using Steno\u2019s principles, with names derived from the characteristics of the rocks in those areas. The figure of this geologic time scale shows the names of the units and subunits. Using this time scale, geologists can place all events of Earth history in order without ever knowing their numerical ages. The specific events within Earth history are discussed in <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/8-earth-history\/\">Chapter 8<\/a>. \u00a0<\/span><\/p>\n<h2><span style=\"font-weight: 400\">7.1 Relative Dating<\/span><\/h2>\n<figure id=\"attachment_3218\" aria-describedby=\"caption-attachment-3218\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.1_Geologic_time_scale.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-465 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.1_Geologic_time_scale-300x300.gif\" alt=\"Chart showing the names of the unit of the Geooogic Time Scale\" width=\"300\" height=\"300\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.1_Geologic_time_scale-300x300.gif 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.1_Geologic_time_scale-150x150.gif 150w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.1_Geologic_time_scale-65x65.gif 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.1_Geologic_time_scale-225x226.gif 225w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3218\" class=\"wp-caption-text\">Geoloigic Time Scale<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\"><strong>Relative dating<\/strong> is the process of determining if one rock or geologic event is older or younger than another, without knowing their specific ages\u2014i.e., how many years ago the object was formed. The principles of relative time are simple, even obvious now, but were not generally accepted by scholars until the scientific revolution of the 17th and 18th centuries<\/span><span style=\"font-weight: 400\">. James Hutton (see <a href=\"http:\/\/opengeology.org\/textbook\/1-understanding-science\/#14_Foundations_of_Modern_Geology\">Chapter 1<\/a>) realized geologic processes are slow and his ideas on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1736\">uniformitarianism<\/a> (i.e., \u201cthe present is the key to the past\u201d) provided a basis for interpreting rocks of the Earth using scientific principles.<\/span><\/p>\n<h3><\/h3>\n<h3><\/h3>\n<h3>7.1.1 Relative Dating Principles<\/h3>\n<p><b>Stratigraphy <\/b>is the study of layered sedimentary rocks. This section discusses principles of relative time used in all of geology, but are especially useful in stratigraphy.<\/p>\n<figure id=\"attachment_3219\" aria-describedby=\"caption-attachment-3219\" style=\"width: 228px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.2_IsfjordenSuperposition.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-466 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition-228x300.jpg\" alt=\"Photo of superposed strata with the younger on top of the older\" width=\"228\" height=\"300\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition-228x300.jpg 228w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition-780x1024.jpg 780w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition-768x1009.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition-1170x1536.jpg 1170w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition-65x85.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition-225x295.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition-350x460.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.2_IsfjordenSuperposition.jpg 1392w\" sizes=\"auto, (max-width: 228px) 100vw, 228px\" \/><\/a><figcaption id=\"caption-attachment-3219\" class=\"wp-caption-text\">Lower strata are older than those lying on top of them.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><b><b>Principle of Superposition: <\/b><\/b>In an otherwise undisturbed sequence of sedimentary strata, or rock layers, the layers on the bottom are the oldest and layers above them are younger.<\/p>\n<p><b><b>Principle of Original Horizontality: <\/b><\/b>Layers of rocks deposited from above, such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1751\">lava<\/a> flows, are originally laid down horizontally. The exception to this principle is at the margins of basins, where the strata can slope slightly downward into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_508\">basin<\/a>.<\/p>\n<figure id=\"attachment_3220\" aria-describedby=\"caption-attachment-3220\" style=\"width: 420px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-467\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995-300x105.jpg\" alt=\"Photo of Grand Canyon strata showing that they are continuous across the canyon\" width=\"420\" height=\"147\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995-300x105.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995-768x270.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995-65x23.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995-225x79.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995-350x123.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.5_lateral_continuity_Grandview_Point_Grand_Canyon_April_1995.jpg 800w\" sizes=\"auto, (max-width: 420px) 100vw, 420px\" \/><\/a><figcaption id=\"caption-attachment-3220\" class=\"wp-caption-text\">Lateral continuity<\/figcaption><\/figure>\n<p><b>Principle of Lateral Continuity: <\/b>Within the depositional <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_508\">basin<\/a>, strata are continuous in all directions until they thin out at the edge of that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_508\">basin<\/a>. Of course, all strata eventually end, either by hitting a geographic barrier, such as a ridge, or when the depositional process extends too far from its source, either a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediment<\/a> source or a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_228\">volcano<\/a>. Strata that are cut by a canyon later remain continuous on either side of the canyon.<\/p>\n<figure id=\"attachment_3221\" aria-describedby=\"caption-attachment-3221\" style=\"width: 225px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.6_Multiple_Igneous_Intrusion_Phases_Kosterhavet_Sweden.jpg\"><img decoding=\"async\" class=\"wp-image-468 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3221\" class=\"wp-caption-text\">CC BY 2.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AMultiple_Igneous_Intrusion_Phases_Kosterhavet_Sweden.jpg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.6_Multiple_Igneous_Intrusion_Phases_Kosterhavet_Sweden-225&#215;300.jpg\u00a0\u00bb alt=\u00a0\u00bbPhoto of rock outcrop with a dike cutting through an older rock and another dike cutting across that one.\u00a0\u00bb width=\u00a0\u00bb225&Prime; height=\u00a0\u00bb300&Prime;&gt; Dark dike cutting across older rocks, the lighter of which is younger than the grey rock.<\/figcaption><\/figure>\n<p><b>Principle of Cross-Cutting Relationships:<\/b><span style=\"font-weight: 400\">\u00a0 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_495\">Deformation<\/a> events like <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_502\">folds<\/a>, faults and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a> intrusions that cut across rocks are younger than the\u00a0<\/span><span style=\"font-weight: 400\">rocks they cut across<\/span><span style=\"font-weight: 400\"><span style=\"font-weight: 400\"><span style=\"font-weight: 400\">.\u00a0<\/span><\/span><\/span><\/p>\n<p><strong>Principle of I<\/strong><b>nclusions: <\/b><span style=\"font-weight: 400\">When one rock formation contains pieces or inclusions of another rock, the included rock is older than the host rock.<\/span><\/p>\n<figure id=\"attachment_3222\" aria-describedby=\"caption-attachment-3222\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.7_Faunal_sucession.jpg\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-469 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.7_Faunal_sucession-300x220.jpg\" alt=\"Diagram showing layers containing fossils. Lines correlating the strata with equivalent fossil content.\" width=\"300\" height=\"220\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.7_Faunal_sucession-300x220.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.7_Faunal_sucession-65x48.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.7_Faunal_sucession-225x165.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.7_Faunal_sucession-350x256.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.7_Faunal_sucession.jpg 717w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3222\" class=\"wp-caption-text\">Fossil succession showing correlation among strata.<\/figcaption><\/figure>\n<p><strong><b>Principle<\/b> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">Fossil<\/a> Succession:<\/strong>Evolution has produced a succession of unique <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> that correlate to the units of the geologic time scale. Assemblages of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> contained in strata are unique to the time they lived, and can be used to correlate rocks of the same age across a wide geographic distribution. Assemblages of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> refers to groups of several unique <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> occurring together.<\/p>\n<h3><b>7.1.2 Grand Canyon Example<\/b><\/h3>\n<figure id=\"attachment_3223\" aria-describedby=\"caption-attachment-3223\" style=\"width: 392px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.8_Grand_canyon_march_2013.jpg\"><img decoding=\"async\" class=\"wp-image-470\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3223\" class=\"wp-caption-text\">www.tomascastelazo.com<\/a>&amp;nbsp;\/&amp;nbsp;<a href=\"&quot;\/wiki\/Main_Page&quot;\" title=\"&quot;Main\">Wikimedia Commons<\/a>, <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AGrand_canyon_march_2013.jpg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.8_Grand_canyon_march_2013-300&#215;200.jpg\u00a0\u00bb alt=\u00a0\u00bbPhoto of the Grand Canyon showing expanse of canyon and the various rock layers\u00a0\u00bb width=\u00a0\u00bb392&Prime; height=\u00a0\u00bb262&Prime;&gt; The Grand Canyon of Arizona<\/figcaption><\/figure>\n<p>The Grand Canyon of Arizona illustrates the stratigraphic principles. The photo shows layers of rock on top of one another in order, from the oldest at the bottom to the youngest at the top, based on the principle of superposition. The predominant white layer just below the canyon rim is the Coconino Sandstone. This layer is laterally continuous, even though the intervening canyon separates its outcrops. The rock layers exhibit the principle of lateral continuity, as they are found on both sides of the Grand Canyon which has been carved by the Colorado River.<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3224\" aria-describedby=\"caption-attachment-3224\" style=\"width: 450px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.3_Stratigraphy_of_the_Grand_Canyon.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-471\" title=\"Image in the public domain.\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.3_Stratigraphy_of_the_Grand_Canyon.png\" alt=\"Diagram showing the three classes of rocks in the Grand Canyon: the oldest metamorphic and granitic rocks of the inner gorge, the tilted and block faulted strata of the later Precambrian Grand Canyon Supergroup, and the horizontal Paleozoic strata of the canyon walls.\" width=\"450\" height=\"614\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.3_Stratigraphy_of_the_Grand_Canyon.png 600w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.3_Stratigraphy_of_the_Grand_Canyon-220x300.png 220w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.3_Stratigraphy_of_the_Grand_Canyon-65x89.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.3_Stratigraphy_of_the_Grand_Canyon-225x307.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.3_Stratigraphy_of_the_Grand_Canyon-350x478.png 350w\" sizes=\"auto, (max-width: 450px) 100vw, 450px\" \/><\/a><figcaption id=\"caption-attachment-3224\" class=\"wp-caption-text\">The rocks of the Grand Canyon<\/figcaption><\/figure>\n<p>The diagram called \u201cGrand Canyon\u2019s Three Sets of Rocks\u201d shows a cross-section of the rocks exposed on the walls of the Grand Canyon, illustrating the principle of cross-cutting relationships, superposition, and original horizontality. In the lowest parts of the Grand Canyon are the oldest sedimentary formations, with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a> and metamorphic rocks at the bottom. The principle of cross-cutting relationships shows the sequence of these events. The metamorphic schist (#16) is the oldest rock formation and the cross-cutting <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1014\">granite<\/a> intrusion (#17) is younger. As seen in the figure, the other layers on the walls of the Grand Canyon are numbered in reverse order with #15 being the oldest and #1 the youngest. This illustrates the principle of superposition. The Grand Canyon region lies in Colorado Plateau, which is characterized by horizontal or nearly horizontal strata, which follows the principle of original horizontality. These rock strata have been barely disturbed from their original <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1757\">deposition<\/a>, except by a broad regional uplift.<\/p>\n<figure id=\"attachment_3225\" aria-describedby=\"caption-attachment-3225\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Grand_Canyon_Nonconformity.jpg\"><img decoding=\"async\" class=\"wp-image-472 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3225\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AGrand_Canyon_with_Snow_4.JPG&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Grand_Canyon_Nonconformity-300&#215;225.jpg\u00a0\u00bb alt=\u00a0\u00bbThe red rocks are layered, the dark rocks are not.\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb225&Prime;&gt; The red, layered rocks of the Grand Canyon Supergroup overlying the dark-colored rocks of the Vishnu schist represents a type of unconformity called a nonconformity.<\/figcaption><\/figure>\n<p>The photo of the Grand Canyon here show strata that were originally deposited in a flat layer on top of older <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a> and metamorphic \u201cbasement\u201d rocks, per the original horizontality principle. Because the formation of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1023\">basement<\/a> rocks and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1757\">deposition<\/a> of the overlying strata is not continuous but broken by events of metamorphism, intrusion, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1755\">erosion<\/a>, the contact between the strata and the older <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1023\">basement<\/a> is termed an <strong>unconformity<\/strong>. An unconformity represents a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">period<\/a> during which <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1757\">deposition<\/a> did not occur or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1755\">erosion<\/a> removed rock that had been deposited, so there are no rocks that represent events of Earth history during that span of time at that place. Unconformities appear in cross sections and stratigraphic columns as wavy lines between formations. Unconformities are discussed in the next section.<\/p>\n<h3><b>7.1.3 Unconformities<\/b><\/h3>\n<figure id=\"attachment_3226\" aria-describedby=\"caption-attachment-3226\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-473 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon-300x225.jpg\" alt=\"The three rock layers are shown.\" width=\"300\" height=\"225\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon-300x225.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon-768x576.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon-65x49.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon-225x169.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon-350x263.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Redwall_Temple_Butte_and_Muav_formations_in_Grand_Canyon.jpg 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3226\" class=\"wp-caption-text\">All three of these formations have a disconformity at the two contacts between them. The pinching Temple Butte is the easiest to see the erosion, but even between the Muav and Redwall, there is an unconfomity.<\/figcaption><\/figure>\n<p>There are three types of unconformities, nonconformity, disconformity, and angular unconformity. A nonconformity occurs when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1761\">sedimentary rock<\/a> is deposited on top of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a> and metamorphic rocks as is the case with the contact between the strata and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1023\">basement<\/a> rocks at the bottom of the Grand Canyon.<\/p>\n<p>The strata in the Grand Canyon represent alternating marine transgressions\u00a0and regressions where sea level rose and fell over millions of years. When the sea level was high marine strata formed. When sea-level fell, the land was exposed to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1755\">erosion<\/a> creating an unconformity. In the Grand Canyon cross-section, this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1755\">erosion<\/a> is shown as heavy wavy lines between the various numbered strata. This is a type of unconformity called a <strong>disconformity<\/strong>, where either non-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1757\">deposition<\/a> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1755\">erosion<\/a> took place. In other words, layers of rock that could have been present, are absent. The time that could have been represented by such layers is instead represented by the disconformity. Disconformities are unconformities that occur between parallel layers of strata indicating either a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">period<\/a> of no <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1757\">deposition<\/a> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1755\">erosion<\/a>.<\/p>\n<figure id=\"attachment_3227\" aria-describedby=\"caption-attachment-3227\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/View_from_Lipan_Point.jpg\"><img decoding=\"async\" class=\"wp-image-474 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3227\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/View_from_Lipan_Point-300&#215;224.jpg\u00a0\u00bb alt=\u00a0\u00bbThe rocks are mostly red.\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb224&Prime;&gt; In the lower part of the picture is an angular unconformity in the Grand Canyon known as the Great Unconformity. Notice flat lying strata over dipping strata (Source: Doug Dolde).<\/figcaption><\/figure>\n<p>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1269\">Phanerozoic<\/a> strata in most of the Grand Canyon are horizontal. \u00a0However, near the bottom horizontal strata overlie tilted strata. This is known as the Great Unconformity and is an example of an <strong>angular unconformity<\/strong>. The lower strata were tilted by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1654\">tectonic<\/a> processes that disturbed their original horizontality and caused the strata to be eroded. Later, horizontal strata were deposited on top of the tilted strata creating the angular unconformity.<\/p>\n<p>Here are three graphical illustrations of the three types of unconformity.<\/p>\n<figure id=\"attachment_3228\" aria-describedby=\"caption-attachment-3228\" style=\"width: 165px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Disconformity.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-475\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Disconformity-300x227.jpg\" alt=\"A disconformity occurs where there is non-deposition or erosion between parallel layers in a depositional sequence\" width=\"165\" height=\"125\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Disconformity-300x227.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Disconformity-65x49.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Disconformity-225x170.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Disconformity-350x264.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Disconformity.jpg 597w\" sizes=\"auto, (max-width: 165px) 100vw, 165px\" \/><\/a><figcaption id=\"caption-attachment-3228\" class=\"wp-caption-text\">Disconformity<\/figcaption><\/figure>\n<p><strong>Disconformity<\/strong>, where is a break or stratigraphic absence between strata in an otherwise parallel sequence of strata.<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3229\" aria-describedby=\"caption-attachment-3229\" style=\"width: 165px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Nonconformity.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-476\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nonconformity-300x226.jpg\" alt=\"A nonconformity occurs where sedimentary strata are deposited on crystalline rocks\" width=\"165\" height=\"124\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nonconformity-300x226.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nonconformity-65x49.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nonconformity-225x170.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nonconformity-350x264.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nonconformity.jpg 596w\" sizes=\"auto, (max-width: 165px) 100vw, 165px\" \/><\/a><figcaption id=\"caption-attachment-3229\" class=\"wp-caption-text\">Nonconformity (the lower rocks are igneous or metamorphic)<\/figcaption><\/figure>\n<p><strong>Nonconformity<\/strong>, where sedimentary strata are deposited on crystalline (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a>\u00a0or metamorphic) rocks.<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3230\" aria-describedby=\"caption-attachment-3230\" style=\"width: 165px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Angular-unconformity.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-477\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Angular-unconformity-300x227.jpg\" alt=\"An angular unconformity develops where sedimentary strata are deposited on strata that have been deformed.\" width=\"165\" height=\"125\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Angular-unconformity-300x227.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Angular-unconformity-65x49.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Angular-unconformity-225x170.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Angular-unconformity-350x265.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Angular-unconformity.jpg 595w\" sizes=\"auto, (max-width: 165px) 100vw, 165px\" \/><\/a><figcaption id=\"caption-attachment-3230\" class=\"wp-caption-text\">Angular unconformity<\/figcaption><\/figure>\n<p><strong>Angular unconformity<\/strong>, where sedimentary strata are deposited on a terrain developed on sedimentary strata that have been deformed by tilting, folding, and\/or faulting. so that they are no longer horizontal.<\/p>\n<h3><\/h3>\n<h3><\/h3>\n<h3><\/h3>\n<h3><\/h3>\n<p>&nbsp;<\/p>\n<h3><span style=\"font-weight: 400\">7.1.3 Applying Relative Dating Principles<\/span><\/h3>\n<figure id=\"attachment_3231\" aria-describedby=\"caption-attachment-3231\" style=\"width: 474px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.4_Block_diagram.jpg\"><img decoding=\"async\" class=\"wp-image-478\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3231\" class=\"wp-caption-text\">CC BY-SA 1.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ACross-cutting_relations.svg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Block_diagram-300&#215;159.jpg\u00a0\u00bb alt=\u00a0\u00bbThe diagram shows many different layers\u00a0\u00bb width=\u00a0\u00bb474&Prime; height=\u00a0\u00bb251&Prime;&gt; Block diagram to apply relative dating principles. The wavy rock is a old metamorphic gneiss, A and F are faults, B is an igneous granite, D is a basaltic dike, and C and E are sedimentary strata.<\/figcaption><\/figure>\n<p>In the block diagram, the sequence of geological events can be determined by using the relative-dating principles and known properties of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a>, sedimentary, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1762\">metamorphic rock<\/a> (see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>, <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">Chapter 5<\/a>, and <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/6-metamorphic-rocks\/\">Chapter 6<\/a>). The sequence begins with the folded metamorphic gneiss on the bottom. Next, the gneiss is cut and displaced by the fault labeled A. Both the gneiss and fault A are cut by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a> granitic intrusion called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1020\">batholith<\/a> B; its irregular outline suggests it is an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a> granitic intrusion emplaced as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1750\">magma<\/a> into the gneiss. Since <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1020\">batholith<\/a> B cuts both the gneiss and fault A, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1020\">batholith<\/a> B is younger than the other two rock formations. Next, the gneiss, fault A, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1020\">batholith<\/a> B were eroded forming a nonconformity as shown with the wavy line. This unconformity was actually an ancient landscape surface on which <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1761\">sedimentary rock<\/a> C was subsequently deposited perhaps by a marine transgression. Next, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a> basaltic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1021\">dike<\/a> D cut through all rocks except <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1761\">sedimentary rock<\/a> E. This shows that there is a disconformity between sedimentary rocks C and E. The top of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1021\">dike<\/a> D is level with the top of layer C, which establishes that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1755\">erosion<\/a> flattened the landscape prior to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1757\">deposition<\/a> of layer E, creating a disconformity between rocks D and E. Fault F cuts across all of the older rocks B, C and E, producing a fault scarp, which is the low ridge on the upper-left side of the diagram. The final events affecting this area are current <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1755\">erosion<\/a> processes working on the land surface, rounding off the edge of the fault scarp, and producing the modern landscape at the top of the diagram.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-43\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-43\" class=\"h5p-iframe\" data-content-id=\"43\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"7.1 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4083\" aria-describedby=\"caption-attachment-4083\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/7.1-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-479 size-thumbnail\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.1-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4083\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 7.1 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">7.2 Absolute Dating<\/span><\/h2>\n<figure id=\"attachment_3232\" aria-describedby=\"caption-attachment-3232\" style=\"width: 407px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Nuvvuagittuq_belt_rocks.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-480\" title=\"NASA, public domain\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nuvvuagittuq_belt_rocks-300x225.jpg\" alt=\"It shows rocks on a shoreline.\" width=\"407\" height=\"305\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nuvvuagittuq_belt_rocks-300x225.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nuvvuagittuq_belt_rocks-65x49.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nuvvuagittuq_belt_rocks-225x169.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nuvvuagittuq_belt_rocks-350x263.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Nuvvuagittuq_belt_rocks.jpg 452w\" sizes=\"auto, (max-width: 407px) 100vw, 407px\" \/><\/a><figcaption id=\"caption-attachment-3232\" class=\"wp-caption-text\">Canada&rsquo;s Nuvvuagittuq Greenstone Belt may have the oldest rocks and oldest evidence life on Earth, according to recent studies.<\/figcaption><\/figure>\n<p>Relative time allows scientists to tell the story of Earth events, but does not provide specific numeric ages, and thus, the rate at which geologic processes operate. Based on Hutton\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1736\">principle of uniformitarianism<\/a> (see <a href=\"#14_Foundations_of_Modern_Geology\">Chapter 1<\/a>), early geologists surmised geological processes work slowly and the Earth is very old. Relative dating principles was how scientists interpreted Earth history until the end of the 19th Century. Because science advances as technology advances, the discovery of radioactivity in the late 1800s provided scientists with a new scientific tool called <strong>radioisotopic dating<\/strong>. Using this new technology, they could assign specific time units, in this case years, to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> grains within a rock. These numerical values are not dependent on comparisons with other rocks such as with relative dating, so this dating method is called <strong>absolute dating<\/strong>. There are several types of absolute dating discussed in this section but radioisotopic dating is the most common and therefore is the focus on this section.<\/p>\n<h3><b>7.2.1 Radioactive Decay<\/b><\/h3>\n<figure id=\"attachment_3233\" aria-describedby=\"caption-attachment-3233\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Isotopes-of-hydrogen.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-481 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Isotopes-of-hydrogen-300x154.jpg\" alt=\"Three isotopes of hydrogen differing in the number of neutrons.\" width=\"300\" height=\"154\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Isotopes-of-hydrogen-300x154.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Isotopes-of-hydrogen-1024x526.jpg 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Isotopes-of-hydrogen-768x394.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Isotopes-of-hydrogen-65x33.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Isotopes-of-hydrogen-225x116.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Isotopes-of-hydrogen-350x180.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Isotopes-of-hydrogen.jpg 1155w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3233\" class=\"wp-caption-text\">Three isotopes of hydrogen<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">All <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">elements<\/a> on the Periodic Table of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">Elements<\/a> (see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/3-minerals\/\">Chapter 3<\/a>) contain <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a>. An <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a> is an atom of an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">element<\/a> with a different number of neutrons. For example, hydrogen (H) always has 1 proton in its nucleus (the atomic number), but the number of neutrons can vary among the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a> (0, 1, 2). Recall that the number of neutrons added to the atomic number gives the atomic mass. When hydrogen has 1 proton and 0 neutrons it is sometimes called protium (<sup>1<\/sup>H<\/span><span style=\"font-weight: 400\">), when hydrogen has 1 proton and 1 neutron it is called deuterium (<sup>2<\/sup>H<\/span><span style=\"font-weight: 400\">), and when hydrogen has 1 proton and 2 neutrons it is called tritium (<sup>3<\/sup>H<\/span><span style=\"font-weight: 400\">).<\/span><\/p>\n<p>Many <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">elements<\/a> have both stable and unstable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a>. For the hydrogen example, <sup>1<\/sup>H and <sup>2<\/sup>H are stable, but <sup>3<\/sup>H is unstable. Unstable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a>, called <strong>radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a><\/strong>, spontaneously decay over time releasing subatomic particles or energy in a process called <strong>radioactive decay<\/strong>. When this occurs, an unstable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a> becomes a more stable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a> of another <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">element<\/a>. For example, carbon-14 (<sup>14<\/sup>C) decays to nitrogen-14 (<sup>14<\/sup>N).<\/p>\n<figure id=\"attachment_3234\" aria-describedby=\"caption-attachment-3234\" style=\"width: 140px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Halflife-sim.gif\"><img decoding=\"async\" class=\"wp-image-482\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3234\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Halflife-sim.gif\u00a0\u00bb alt=\u00a0\u00bbThe many looks more smooth\u00a0\u00bb width=\u00a0\u00bb140&Prime; height=\u00a0\u00bb263&Prime;&gt; Simulation of half-life. On the left, 4 simulations with only a few atoms. On the right, 4 simulations with many atoms.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p>The radioactive decay of any individual atom is a completely unpredictable and random event. However, some rock specimens have an enormous number of radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a>, perhaps trillions of atoms, and this large group of radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a> does have a predictable pattern of radioactive decay. The radioactive decay of <em>half<\/em> of the radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a> in this group takes a specific amount of time. The time it takes for half of the atoms in a substance to decay is called the <strong>half-life<\/strong>. In other words, the half-life of an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a> is the amount of time it takes for half of a group of unstable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a> to decay to a stable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a>. The half-life is constant and measurable for a given radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a>, so it can be used to calculate the age of a rock. For example, the half-life uranium-238 (<sup>238<\/sup>U) is 4.5 billion years and the half-life of <sup>14<\/sup>C is 5,730 years.<\/p>\n<p>The principles behind this dating method require two key assumptions. First, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> grains containing the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a> formed at the same time as the rock, such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a> in an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous rock<\/a> that crystallized from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1750\">magma<\/a>. Second, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> crystals remain a closed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1742\">system<\/a>, meaning they are not subsequently altered by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">elements<\/a> moving in or out of them.<\/p>\n<figure id=\"attachment_3152\" aria-describedby=\"caption-attachment-3152\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.1-03-Granite-vs-Gneiss.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-434 size-medium\" title=\"Source: Peter Davis\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/06.1-03-Granite-vs-Gneiss-300x130.jpg\" alt=\"Two rocks with very similar colors. One is a granite and another is a gneiss that has aligned dark minerals.\" width=\"300\" height=\"130\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/06.1-03-Granite-vs-Gneiss-300x130.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/06.1-03-Granite-vs-Gneiss-1024x443.jpg 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/06.1-03-Granite-vs-Gneiss-768x332.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/06.1-03-Granite-vs-Gneiss-65x28.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/06.1-03-Granite-vs-Gneiss-225x97.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/06.1-03-Granite-vs-Gneiss-350x151.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/06.1-03-Granite-vs-Gneiss.jpg 1175w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3152\" class=\"wp-caption-text\">Granite (left) and gneiss (right). Dating a mineral within the granite would give the crystallization age of the rock, while dating the gneiss might reflect the timing of metamorphism.<\/figcaption><\/figure>\n<p>These requirements place some constraints on the kinds of rock suitable for dating, with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous rock<\/a> being the best. Metamorphic rocks are crystalline, but the processes of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1762\">metamorphism<\/a> may reset the clock and derived ages may represent a smear of different metamorphic events rather than the age of original <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1752\">crystallization<\/a>. Detrital sedimentary rocks contain clasts from separate <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1766\">parent rocks<\/a> from unknown locations and derived ages are thus meaningless. However, sedimentary rocks with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1785\">precipitated<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a>, such as evaporites, may contain <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">elements<\/a> suitable for radioisotopic dating. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">Igneous<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1004\">pyroclastic<\/a> layers and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1751\">lava<\/a><span style=\"font-size: 1em\">\u00a0flows within a sedimentary sequence can be used to date the sequence. Cross-cutting <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a> rocks and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1022\">sills<\/a> can be used to bracket the ages of affected, older sedimentary rocks. The resistant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a>, found as clasts in many ancient sedimentary rocks, has been successfully used for establishing very old dates, including the age of Earth\u2019s oldest known rocks. Knowing that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a> in metamorphosed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a> came from older rocks that are no longer available for study, scientists can date <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a> to establish the age of the pre-metamorphic source rocks.<\/span><\/p>\n<figure id=\"attachment_3236\" aria-describedby=\"caption-attachment-3236\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Alpha_Decay.svg_.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-483 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Alpha_Decay.svg_-300x204.png\" alt=\"Two protons and two neutrons leave the nucleus.\" width=\"300\" height=\"204\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Alpha_Decay.svg_-300x204.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Alpha_Decay.svg_-65x44.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Alpha_Decay.svg_-225x153.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Alpha_Decay.svg_-350x238.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Alpha_Decay.svg_.png 500w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3236\" class=\"wp-caption-text\">An alpha decay: Two protons and two neutrons leave the nucleus.<\/figcaption><\/figure>\n<p>There are several ways radioactive atoms decay.\u00a0 We will consider three of them here\u2014<b>alpha decay, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1223\">beta decay<\/a>, <\/b>and<b> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1225\">electron capture<\/a><\/b><span style=\"font-weight: 400\">. <\/span><strong>Alpha decay<\/strong> is when an alpha particle, which consists of two protons and two neutrons, is emitted from the nucleus of an atom. This also happens to be the nucleus of a helium atom; helium gas may get trapped in the crystal lattice of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> in which alpha decay has taken place. When an atom loses two protons from its nucleus, lowering its atomic number, it is transformed into an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">element<\/a> that is two atomic numbers lower on the Periodic Table of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">Elements<\/a>.<\/p>\n<figure id=\"attachment_3237\" aria-describedby=\"caption-attachment-3237\" style=\"width: 477px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.11_periodic_table.png\"><img decoding=\"async\" class=\"wp-image-484\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3237\" class=\"wp-caption-text\">CC BY-SA 4.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3APeriodic_Table_Chart.png&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.11_periodic_table-300&#215;160.png\u00a0\u00bb alt=\u00a0\u00bbSimplified Periodic Table of the Elements\u00a0\u00bb width=\u00a0\u00bb477&Prime; height=\u00a0\u00bb254&Prime;&gt; Periodic Table of the Elements<\/figcaption><\/figure>\n<p>The loss of four particles, in this case two neutrons and two protons, also lowers the mass of the atom by four. For example alpha decay takes place in the unstable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a> <sup>238<\/sup>U, which has an atomic number of 92 (92 protons) and mass number of 238 (total of all protons and neutrons). When <sup>238<\/sup>U spontaneously emits an alpha particle, it becomes thorium-234 (<sup>234<\/sup>Th). The radioactive decay product of an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">element<\/a> is called its <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1222\">daughter isotope<\/a><\/strong> and the original <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">element<\/a> is called the <strong>parent isotope<\/strong>. In this case, <sup>238<\/sup>U is the parent isotope and <sup>234<\/sup>Th is the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1222\">daughter isotope<\/a>. The half-life of <sup>238<\/sup>U is 4.5 billion years, i.e., the time it takes for half of the parent isotope atoms to decay into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1222\">daughter isotope<\/a>. This isotope of uranium, <sup>238<\/sup>U, can be used for absolute dating the oldest materials found on Earth, and even <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1254\">meteorites<\/a>\u00a0and materials from the earliest events in our <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1253\">solar system<\/a>.<\/p>\n<figure id=\"attachment_3238\" aria-describedby=\"caption-attachment-3238\" style=\"width: 198px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/U-238-decay-chain.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-485 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/U-238-decay-chain-198x300.jpg\" alt=\"Decay chain of U-238 to stable Pb-206 through a series of alpha and beta decays.\" width=\"198\" height=\"300\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/U-238-decay-chain-198x300.jpg 198w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/U-238-decay-chain-676x1024.jpg 676w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/U-238-decay-chain-768x1164.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/U-238-decay-chain-65x98.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/U-238-decay-chain-225x341.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/U-238-decay-chain-350x530.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/U-238-decay-chain.jpg 790w\" sizes=\"auto, (max-width: 198px) 100vw, 198px\" \/><\/a><figcaption id=\"caption-attachment-3238\" class=\"wp-caption-text\">Decay chain of U-238 to stable Pb-206 through a series of alpha and beta decays.<\/figcaption><\/figure>\n<p><b>B<\/b><\/p>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1223\">Beta decay<\/a> is when a neutron in its nucleus splits into an electron and a proton. The electron is emitted from the nucleus as a beta ray. The new proton increases the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">element<\/a>\u2019s atomic number by one, forming a new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">element<\/a> with the same atomic mass as the parent isotope. For example, <sup>234<\/sup>Th is unstable and undergoes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1223\">beta decay<\/a> to form protactinium-234 (<sup>234<\/sup>Pa), which also undergoes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1223\">beta decay<\/a> to form uranium-234 (<sup>234<\/sup>U). Notice these are all isotopes of different <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">elements<\/a> but they have the same atomic mass of 234. The decay process of radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">elements<\/a> like uranium keeps producing radioactive parents and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1222\">daughters<\/a> until a stable, or non-radioactive, daughter is formed. Such a series is called a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1224\">decay chain<\/a><\/strong>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1224\">decay chain<\/a> of the radioactive parent isotope <sup>238<\/sup>U progresses through a series of alpha (red arrows on the adjacent figure) and beta decays (blue arrows), until it forms the stable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1222\">daughter isotope<\/a>, lead-206 (<sup>206<\/sup>Pb).<\/p>\n<figure id=\"attachment_3239\" aria-describedby=\"caption-attachment-3239\" style=\"width: 254px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Atomic_rearrangement_following_an_electron_capture.svg_.png\"><img decoding=\"async\" class=\"wp-image-486 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3239\" class=\"wp-caption-text\">CC BY-SA 4.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AAtomic_rearrangement_following_an_electron_capture.svg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Atomic_rearrangement_following_an_electron_capture.svg_-254&#215;300.png\u00a0\u00bb alt=\u00a0\u00bbIt shows two paths\u00a0\u00bb width=\u00a0\u00bb254&Prime; height=\u00a0\u00bb300&Prime;&gt; The two paths of electron capture<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1225\">Electron capture<\/a><\/strong> is when a proton in the nucleus captures an electron from one of the electron shells and becomes a neutron. This produces one of two different effects: 1) an electron jumps in to fill the missing spot of the departed electron and emits an X-ray, or 2) in what is called the Auger process, another electron is released and changes the atom into an ion. The atomic number is reduced by one and mass number remains the same. An example of an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">element<\/a> that decays by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1225\">electron capture<\/a> is potassium-40 (<sup>40<\/sup>K). Radioactive <sup>40<\/sup>K makes up a tiny percentage (0.012%) of naturally occurring potassium, most of which not radioactive. <sup>40<\/sup>K decays to argon-40 (<sup>40<\/sup>Ar) with a half-life of 1.25 billion years, so it is very useful for dating geological events<\/span><span style=\"font-weight: 400\">. <\/span>Below is a table of some of the more commonly-used radioactive dating <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a> and their half-lives.<\/p>\n<table>\n<tbody>\n<tr>\n<td><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">Elements<\/a><\/b><\/td>\n<td><b>Parent symbol<\/b><\/td>\n<td><b>Daughter symbol<\/b><\/td>\n<td><b>Half-life<\/b><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Uranium-238\/Lead-206<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>238<\/sup>U<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>206<\/sup>Pb<\/span><\/td>\n<td><span style=\"font-weight: 400\">4.5 billion years<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Uranium-235\/Lead-207<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>235<\/sup>U<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>207<\/sup>Pb<\/span><\/td>\n<td><span style=\"font-weight: 400\">704 million years<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Potassium-40\/Argon-40<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>40<\/sup>K<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>40<\/sup>Ar<\/span><\/td>\n<td><span style=\"font-weight: 400\">1.25 billion years<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Rubidium-87\/Strontium-87<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>87<\/sup>Rb<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>87<\/sup>Sr<\/span><\/td>\n<td><span style=\"font-weight: 400\">48.8 billion years<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400\">Carbon-14\/Nitrogen-14<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>14<\/sup>C<\/span><\/td>\n<td><span style=\"font-weight: 400\"><sup>14<\/sup>N<\/span><\/td>\n<td><span style=\"font-weight: 400\">5,730 years<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><em>Some common <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\"><em>isotopes<\/em><\/a> used for radioisotopic dating.<\/em><\/p>\n<h3><b>7.2.2 Radioisotopic Dating<\/b><\/h3>\n<figure id=\"attachment_3240\" aria-describedby=\"caption-attachment-3240\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.14_Mass_spectrometer.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-487 size-medium\" title=\"This is a copyrighted image from the CAMECA Archives Reproduction is authorized, under the terms of the GNU Free Documentation License.\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.14_Mass_spectrometer-300x213.jpg\" alt=\"Photo of mass spectrometer\" width=\"300\" height=\"213\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.14_Mass_spectrometer-300x213.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.14_Mass_spectrometer-65x46.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.14_Mass_spectrometer-225x160.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.14_Mass_spectrometer-350x249.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.14_Mass_spectrometer.jpg 586w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3240\" class=\"wp-caption-text\">Mass spectrometer instrument<\/figcaption><\/figure>\n<p>For a given a sample of rock, how is the dating procedure carried out? The parent and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1222\">daughter isotopes<\/a>\u00a0are separated out of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> using chemical extraction. In the case of uranium, <sup>238<\/sup>U and <sup>235<\/sup>U <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a> are separated out together, as are the <sup>206<\/sup>Pb and <sup>207<\/sup>Pb with an instrument called a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1226\">mass spectrometer<\/a><span style=\"font-weight: 400\">.\u00a0<\/span><\/p>\n<figure id=\"attachment_3241\" aria-describedby=\"caption-attachment-3241\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Half_times.svg_.png\"><img decoding=\"async\" class=\"wp-image-488 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3241\" class=\"wp-caption-text\">CC0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AHalf_times.svg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Half_times.svg_-300&#215;300.png\u00a0\u00bb alt=\u00a0\u00bbThe graph gets progressively taller\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb300&Prime;&gt; Graph of amount of half life vs. amount of daughter isotope.<\/figcaption><\/figure>\n<p>Here is a simple example of age calculation using the daughter-to-parent ratio of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a>. When the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> initially forms, it consists of 0% daughter and 100% parent isotope, so the daughter-to-parent ratio (D\/P) is 0. After one half-life, half the parent has decayed so there is 50% daughter and 50% parent, a 50\/50 ratio, with D\/P = 1. After two <u>half-lives<\/u>, there is 75% daughter and 25% parent (75\/25 ratio) and D<u>\/P = <\/u>3. This can be further calculated for a series of half-lives as shown in the table. The table does not show more than 10 half-lives because after about 10 half-lives, the amount of remaining parent is so small it becomes too difficult to accurately measure via chemical analysis. Modern applications of this method have achieved remarkable accuracies of plus or minus two million years in 2.5 billion years (that\u2019s \u00b10.055%). Applying the uranium\/lead technique in any given sample analysis provides two separate clocks running at the same time, <sup>238<\/sup>U and <sup>235<\/sup>U. The existence of these two clocks in the same sample gives a cross-check between the two. Many geological samples contain multiple parent\/daughter pairs, so cross-checking the clocks confirms that radioisotopic dating is highly reliable.<\/p>\n<table>\n<tbody>\n<tr style=\"height: 111px\">\n<td style=\"height: 111px\"><b>Half-lives<\/b><\/p>\n<p><b>(#)<\/b><\/td>\n<td style=\"height: 111px\"><b>Parent present (%)<\/b><\/td>\n<td style=\"height: 111px\"><b>Daughter present <\/b><\/p>\n<p><b>(%)<\/b><\/td>\n<td style=\"height: 111px\"><b>Daughter\/<\/b><\/p>\n<p><b>Parent ratio<\/b><\/td>\n<td style=\"height: 111px\"><b>Parent\/ <\/b><\/p>\n<p><b>Daughter ratio<\/b><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">Start the clock<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">100<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0<\/span><\/td>\n<td style=\"height: 27px\">\u00a0infinite<\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">1<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">50<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">50<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">1<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">1<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">2<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">25<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">75<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">3<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.33<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">3<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">12.5<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">87.5<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">7<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.143<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">4<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">6.25<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">93.75<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">15<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.0667<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27.9277px\">\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">5<\/span><\/td>\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">3.125<\/span><\/td>\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">96.875<\/span><\/td>\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">31<\/span><\/td>\n<td style=\"height: 27.9277px\"><span style=\"font-weight: 400\">0.0325<\/span><\/td>\n<\/tr>\n<tr style=\"height: 27px\">\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">10<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.098<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">99.9<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">1023<\/span><\/td>\n<td style=\"height: 27px\"><span style=\"font-weight: 400\">0.00098<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><em>Ratio of parent to daughter in terms of <em>half-life<\/em>.<\/em><\/p>\n<figure id=\"attachment_3242\" aria-describedby=\"caption-attachment-3242\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Accelerator_mass_spectrometer_schematic_for_radiocarbon.svg_.png\"><img decoding=\"async\" class=\"wp-image-489 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3242\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AAccelerator_mass_spectrometer_schematic_for_radiocarbon.svg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Accelerator_mass_spectrometer_schematic_for_radiocarbon.svg_-300&#215;111.png\u00a0\u00bb alt=\u00a0\u00bbIt shows the isotopes separating\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb111&Prime;&gt; Schematic of carbon going through a mass spectrometer.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Another radioisotopic dating method involves carbon and is useful for dating archaeologically important samples containing organic substances like wood or bone. <strong>Radiocarbon dating<\/strong>, also called carbon dating, uses the unstable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a> carbon-14 (<sup>14<\/sup>C) and the stable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a> carbon-12 (<sup>12<\/sup>C). Carbon-14 is constantly being created in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1745\">atmosphere<\/a> by the interaction of cosmic particles with atmospheric nitrogen-14 (<sup>14<\/sup>N)<\/span><span style=\"font-weight: 400\">. Cosmic particles such as neutrons <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_500\">strike<\/a> the nitrogen nucleus, kicking out a proton but leaving the neutron in the nucleus. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1698\">collision<\/a> reduces the atomic number by one, changing it from seven to six, changing the nitrogen into carbon with the same mass number of 14. The <sup>14<\/sup>C quickly <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1781\">bonds<\/a> with oxygen (O) in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1745\">atmosphere<\/a> to form carbon dioxide (<sup>14<\/sup>CO<sub>2<\/sub>) that mixes with other atmospheric carbon dioxide (<sup>12<\/sup>CO<sub>2<\/sub>) and this mix of gases is incorporated into living matter. While an organism is alive, the ratio of <sup>14<\/sup>C\/<sup>12<\/sup>C in its body doesn\u2019t really change since CO<sub>2<\/sub> is constantly exchanged with the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1745\">atmosphere<\/a>. However, when it dies, the radiocarbon clock starts ticking as the <sup>14<\/sup>C decays back to <sup>14<\/sup>N by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1223\">beta decay<\/a>, which has a half-life of 5,730 years. The radiocarbon dating technique is thus useful for 57,300 years or so, about 10 half-lives back.<\/span><\/p>\n<figure id=\"attachment_3243\" aria-describedby=\"caption-attachment-3243\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Carbon_Dioxide_400kyr.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-490 size-medium\" title=\"by Robert A. Rohde\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Carbon_Dioxide_400kyr-300x218.png\" alt=\"It varies, but spikes in recent past.\" width=\"300\" height=\"218\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Carbon_Dioxide_400kyr-300x218.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Carbon_Dioxide_400kyr-65x47.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Carbon_Dioxide_400kyr-225x164.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Carbon_Dioxide_400kyr-350x254.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Carbon_Dioxide_400kyr.png 600w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3243\" class=\"wp-caption-text\">Carbon dioxide concentrations over the last 400,000 years.<\/figcaption><\/figure>\n<p>Radiocarbon dating relies on daughter-to-parent ratios derived from a known quantity of parent <sup>14<\/sup>C. Early applications of carbon dating assumed the production and concentration of <sup>14<\/sup>C in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1745\">atmosphere<\/a> remained fairly constant for the last 50,000 years. However, it is now known that the amount of parent <sup>14<\/sup>C levels in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1745\">atmosphere<\/a> has varied. Comparisons of carbon ages with tree-ring data and other data for known events have allowed reliable calibration of the radiocarbon dating method. Taking into account carbon-14 baseline levels must be calibrated against other reliable dating methods, carbon dating has been shown to be a reliable method for dating archaeological specimens and very recent geologic events.<\/p>\n<h3><b>7.2.3 Age of the Earth<\/b><\/h3>\n<figure id=\"attachment_3244\" aria-describedby=\"caption-attachment-3244\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Hadean.png\"><img decoding=\"async\" class=\"wp-image-491 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3244\" class=\"wp-caption-text\">CC BY-SA 4.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AHadean.png&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Hadean-300&#215;161.png\u00a0\u00bb alt=\u00a0\u00bbThe surface of Earth is full of volcanoes.\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb161&Prime;&gt; Artist\u2019s impression of Earth in the Hadean Eon, early in Earth\u2019s history.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The work of Hutton and other scientists gained attention after the Renaissance (see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/1-understanding-science\/\">Chapter 1<\/a>), spurring exploration into the idea of an ancient Earth. In the late 19<sup>th<\/sup> century William Thompson, a.k.a. Lord Kelvin, applied his knowledge of physics to develop the assumption that the Earth started as a hot molten sphere. He estimated the Earth is 98 million years old, but because of uncertainties in his calculations stated the age as a range of between 20 and 400 million years<\/span><span style=\"font-weight: 400\">. <\/span><a href=\"https:\/\/youtu.be\/mOSpRzW2i_4\">This animation<\/a> illustrates how Kelvin calculated this range and why his numbers were so far off, which has to do with unequal heat transfer within the Earth. It has also been pointed out that Kelvin failed to consider pliability and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1655\">convection<\/a> in the Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1664\">mantle<\/a> as a heat transfer mechanism. Kelvin\u2019s estimate for Earth\u2019s age was considered plausible but not without challenge, and the discovery of radioactivity provided a more accurate method for determining ancient ages<span style=\"font-weight: 400\">.<\/span><\/p>\n<p><span style=\"font-weight: 400\">In the 1950\u2019s, Clair Patterson (1922\u20131995) thought he could determine the age of the Earth using radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a> from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1254\">meteorites<\/a>, which he considered to be early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1253\">solar system<\/a> remnants that were present at the time Earth was forming. Patterson analyzed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1254\">meteorite<\/a> samples for uranium and lead using a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1226\">mass spectrometer<\/a>. He used the uranium\/lead dating technique in determining the age of the Earth to be 4.55 billion years, give or take about 70 million (\u00b1 1.5%). The current estimate for the age of the Earth is 4.54 billion years, give or take 50 million (\u00b1 1.1%)<\/span><span style=\"font-weight: 400\">. It is remarkable that Patterson, who was still a graduate student at the University of Chicago, came up with a result that has been little altered in over 60 years, even as technology has improved dating methods.<\/span><\/p>\n<h3><b>7.2.4 Dating Geological Events<\/b><\/h3>\n<figure id=\"attachment_3245\" aria-describedby=\"caption-attachment-3245\" style=\"width: 212px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.17_Zircon_microscope.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-492 size-medium\" title=\"Photo by Foto Chd (german wikipedia, https:\/\/de.wikipedia.org\/wiki\/Benutzer:Chd), used under the terms of the GNU Free Documentation License\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.17_Zircon_microscope-212x300.jpg\" alt=\"Photomicrograph of zircon crystal\" width=\"212\" height=\"300\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.17_Zircon_microscope-212x300.jpg 212w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.17_Zircon_microscope-65x92.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.17_Zircon_microscope-225x318.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.17_Zircon_microscope-350x494.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.17_Zircon_microscope.jpg 490w\" sizes=\"auto, (max-width: 212px) 100vw, 212px\" \/><\/a><figcaption id=\"caption-attachment-3245\" class=\"wp-caption-text\">Photomicrograph of zircon crystal<\/figcaption><\/figure>\n<p>Radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a> of<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\"> elements<\/a> that are common in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> crystals are useful for radioisotopic dating. The uranium\/lead method, with its two cross-checking clocks, is most often used with crystals of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a> (ZrSiO<sub>4<\/sub>) where uranium can substitute for zirconium in the crystal lattice. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">Zircon<\/a> is resistant to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1754\">weathering<\/a> which makes it useful for dating geological events in ancient rocks. During metamorphic events, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a> crystals may form multiple crystal layers, with each layer recording the isotopic age of an event, thus tracing the progress of the several metamorphic events<span style=\"font-weight: 400\">.\u00a0<\/span><\/p>\n<p>Geologists have used <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a> grains to do some amazing studies that illustrate how scientific conclusions can change with technological advancements. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">Zircon<\/a> crystals from Western Australia that formed when the crust first differentiated from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1664\">mantle<\/a> 4.4 billion years ago have been determined to be the oldest known rocks. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a> grains were incorporated into metasedimentary host rocks, sedimentary rocks showing signs of having undergone partial metamorphism. The host rocks were not very old but the embedded zircon grains were created 4.4 billion years ago, and survived the subsequent processes of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1754\">weathering<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1755\">erosion<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1757\">deposition<\/a>, and metamorphism. From other properties of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a> crystals, researchers concluded that not only were continental rocks exposed above sea level, but also that conditions on the early Earth were cool enough for liquid water to exist on the surface. The presence of liquid water allowed the processes of weathering and erosion to take place. Researchers at UCLA studied 4.1 billion-year-old <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a> crystals and found carbon in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a> crystals that may be biogenic in origin, meaning that life may have existed on Earth much earlier than previously thought.<\/p>\n<figure id=\"attachment_2557\" aria-describedby=\"caption-attachment-2557\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Yellowstone_volcano_-_ash_beds.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-134 size-medium\" title=\"Public domain, USGS\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Yellowstone_volcano_-_ash_beds-300x195.jpg\" alt=\"The eruptions trend eastward due to prevailing winds.\" width=\"300\" height=\"195\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Yellowstone_volcano_-_ash_beds-300x195.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Yellowstone_volcano_-_ash_beds-65x42.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Yellowstone_volcano_-_ash_beds-225x146.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Yellowstone_volcano_-_ash_beds-350x228.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Yellowstone_volcano_-_ash_beds.jpg 580w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-2557\" class=\"wp-caption-text\">Several prominent ash beds found in North America, including three Yellowstone eruptions shaded pink (Mesa Falls, Huckleberry Ridge, and Lava Creek), the Bisho Tuff ash bed (brown dashed line), and the modern May 18th, 1980 ash fall (yellow).<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">Igneous<\/a> rocks best suited for radioisotopic dating because their primary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a> provide dates of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1752\">crystallization<\/a> from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1750\">magma<\/a>. Metamorphic processes tend to reset the clocks and smear the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous rock<\/a>\u2019s original date. Detrital sedimentary rocks are less useful because they are made of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a> derived from multiple parent sources with potentially many dates. However, scientists can use <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1753\">igneous<\/a> events to date sedimentary sequences. For example, if sedimentary strata are between a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1751\">lava<\/a> flow and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_228\">volcanic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1001\">ash<\/a> bed with radioisotopic dates of 54 million years and 50 million years, then geologists know the sedimentary strata and its <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> formed between 54 and 50 million years ago. Another example would be a 65 million year old <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_228\">volcanic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1021\">dike<\/a> that cut across sedimentary strata. This provides an upper limit age on the sedimentary strata, so this strata would be older than 65 million years. Potassium is common in evaporite <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a> and has been used for potassium\/argon dating<\/span><span style=\"font-weight: 400\">. Primary sedimentary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a> containing radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a> like <sup>40<\/sup>K, has provided dates for important geologic events.<\/span><\/p>\n<h3><span style=\"font-weight: 400\">7.2.5 Other Absolute Dating Techniques<\/span><\/h3>\n<figure id=\"attachment_3246\" aria-describedby=\"caption-attachment-3246\" style=\"width: 451px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Keizars_TLexplained2.jpg\"><img decoding=\"async\" class=\"wp-image-493\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3246\" class=\"wp-caption-text\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0-3.0-2.5-2.0-1.0&quot;\">CC BY-SA 4.0-3.0-2.5-2.0-1.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AKeizars_TLexplained2.jpg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Keizars_TLexplained2.jpg\u00a0\u00bb alt=\u00a0\u00bbThe diagram explains the details of the technique, showing trapped electrons.\u00a0\u00bb width=\u00a0\u00bb451&Prime; height=\u00a0\u00bb372&Prime;&gt; Thermoluminescence, a type of luminescence dating<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\"><strong>Luminescence (aka Thermoluminescence):<\/strong> Radioisotopic dating is not the only way scientists determine numeric ages. Luminescence dating measures the time elapsed since some <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1787\">silicate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a>, such as coarse-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1787\">silicate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a>, were last exposed to light or heat at the surface of Earth. All buried <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a> are exposed to radiation from normal background radiation from the decay process described above. Some of these electrons get trapped in the crystal lattice of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1787\">silicate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a> like <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_967\">quartz<\/a>. When exposed at the surface, ultraviolet radiation and heat from the Sun releases these electrons, but when the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a> are buried just a few inches below the surface, the electrons get trapped again. Samples of coarse <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a> collected just a few feet below the surface are analyzed by stimulating them with light in a lab. This stimulation releases the trapped electrons as a photon of light which is called luminescence. The amount luminescence released indicates how long the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediment<\/a> has been buried. Luminescence dating is only useful for dating young <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a> that are less than 1 million years old. In Utah, luminescence dating is used to determine when coarse-grained <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediment<\/a> layers were buried near a fault. This is one technique used to determine the recurrence interval of large earthquakes on faults like the Wasatch Fault that primarily cut coarse-grained material and lack buried organic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_250\">soils<\/a> for radiocarbon dating.<\/span><\/p>\n<figure id=\"attachment_3247\" aria-describedby=\"caption-attachment-3247\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Apatite-CaF-280343.jpg\"><img decoding=\"async\" class=\"wp-image-494 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3247\" class=\"wp-caption-text\">iRocks.com<\/a> \u2013 CC-BY-SA-3.0 [<a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AApatite-(CaF)-280343.jpg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Apatite-CaF-280343-300&#215;267.jpg\u00a0\u00bb alt=\u00a0\u00bbThe crystal is hexagonal and light green.\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb267&Prime;&gt; Apatite from Mexico.<\/figcaption><\/figure>\n<p><strong>Fission Track:<\/strong> Fission track dating relies on damage to the crystal lattice produced when unstable <sup>238<\/sup>U decays to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1222\">daughter product<\/a> <sup>234<\/sup>Th and releases an alpha particle. These two decay products move in opposite directions from each other through the crystal lattice leaving a visible track of damage. This is common in uranium-bearing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> grains such as apatite. The tracks are large and can be visually counted under an optical microscope. The number of tracks correspond to the age of the grains. Fission track dating works from about 100,000 to 2 billion (1 \u00d7 10<sup>5<\/sup> to 2 \u00d7 10<sup>9<\/sup>) years ago. Fission track dating has also been used as a second clock to confirm dates obtained by other methods.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-44\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-44\" class=\"h5p-iframe\" data-content-id=\"44\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"7.2 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4084\" aria-describedby=\"caption-attachment-4084\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/7.2-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-495 size-thumbnail\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.2-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4084\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 7.2 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">7.3 Fossils and Evolution<\/span><\/h2>\n<figure id=\"attachment_3248\" aria-describedby=\"caption-attachment-3248\" style=\"width: 222px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.3_Archaeopteryx_lithographica.jpg\"><img decoding=\"async\" class=\"wp-image-496 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3248\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a> or <a href=\"denied:&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;\">GFDL<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AArchaeopteryx_lithographica_(Berlin_specimen).jpg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.3_Archaeopteryx_lithographica-222&#215;300.jpg\u00a0\u00bb alt=\u00a0\u00bbImage of the Archaeopteryx fossil that show features of both reptiles and birds. This is a famous transition fossil between reptiles and birds.\u00a0\u00bb width=\u00a0\u00bb222&Prime; height=\u00a0\u00bb300&Prime;&gt; Archaeopteryx lithographica, specimen displayed at the Museum f\u00fcr Naturkunde in Berlin.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">Fossils<\/a><\/strong><\/span>\u00a0are any evidence of past life preserved in rocks. They may be actual remains of body parts (rare), impressions of soft body parts, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1231\">casts<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1232\">molds<\/a> of body parts (more common), body parts replaced by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> (common) or evidence of animal behavior such as footprints and burrows. The body parts of living organisms range from the hard bones and shells of animals, soft cellulose of plants, soft bodies of jellyfish, down to single cells of bacteria and algae. Which body parts can be preserved? The vast majority of life today consists soft-bodied and\/or single celled organisms, and will not likely be preserved in the geologic record except under unusual conditions. The best environment for preservation is the ocean, yet marine processes can dissolve hard parts and scavenging can reduce or eliminate remains. Thus, even under ideal conditions in the ocean, the likelihood of preservation is quite limited. For terrestrial life, the possibility of remains being buried and preserved is even more limited. In other words, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossil<\/a> record is incomplete and records only a small percentage of life that existed. Although incomplete, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossil<\/a> records are used for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1237\">stratigraphic correlation<\/a>, using the Principle of Faunal Succession, and provide a method used for establishing the age of a formation on the Geologic Time Scale.<\/p>\n<h3><span style=\"font-weight: 400\">7.3.1 Types of Preservation<\/span><\/h3>\n<figure id=\"attachment_3249\" aria-describedby=\"caption-attachment-3249\" style=\"width: 148px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/ElrathiakingiUtahWheelerCambrian.jpg\"><img decoding=\"async\" class=\"wp-image-497\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3249\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/ElrathiakingiUtahWheelerCambrian-243&#215;300.jpg\u00a0\u00bb alt=\u00a0\u00bbIt has three lobes\u00a0\u00bb width=\u00a0\u00bb148&Prime; height=\u00a0\u00bb183&Prime;&gt; Trilobites had a hard exoskeleton and are often preserved by permineralization.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Remnants or impressions of hard parts, such as a marine clam shell or dinosaur bone, are the most common types of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a><\/span><span style=\"font-weight: 400\">. <\/span>The original material has almost always been replaced with new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a> that preserve much of the shape of the original shell, bone, or cell. The common types of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossil<\/a> preservation are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1229\">actual preservation<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1230\">permineralization<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1232\">molds<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1231\">casts<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1234\">carbonization<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1235\">trace fossils<\/a>.<\/p>\n<p><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1229\">Actual preservation<\/a> <\/b>is a rare form of fossilization where the original materials or hard parts of the organism are preserved. Preservation of soft-tissue is very rare since these organic materials easily disappear because of bacterial decay<span style=\"font-weight: 400\">.<\/span>\u00a0Examples of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1229\">actual preservation<\/a> are unaltered biological materials like insects in amber or original <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a> like mother-of-pearl on the interior of a shell. Another example is mammoth skin and hair preserved in post-glacial deposits in the Arctic regions<span style=\"font-weight: 400\"><span style=\"font-weight: 400\">.\u00a0 Rare mummification has left fragments of soft tissue, skin, and sometimes even blood vessels of dinosaurs, from which proteins have been isolated and evidence for DNA fragments have been discovered.\u00a0<\/span><\/span><\/p>\n<figure id=\"attachment_3250\" aria-describedby=\"caption-attachment-3250\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.19_mosquito_in_amber-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3250 size-medium\" title=\"This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.19_mosquito_in_amber-scaled-1.jpg\" alt=\"Mosquito trapped in amber in actal preservation\" width=\"300\" height=\"206\" \/><\/a><figcaption id=\"caption-attachment-3250\" class=\"wp-caption-text\">Mosquito preserved in amber<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3253\" aria-describedby=\"caption-attachment-3253\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.20_Petrified_forest_log_2_md-1.jpg\"><img decoding=\"async\" class=\"wp-image-357 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3253\" class=\"wp-caption-text\">CC BY-SA 2.5<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3APetrified_forest_log_2_md.jpg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.20_Petrified_forest_log_2_md-1-300&#215;300.jpg\u00a0\u00bb alt=\u00a0\u00bbPhoto of log of petrified wood showing structures of the original wood\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb300&Prime;&gt; Permineralization in petrified wood<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1230\">Permineralization<\/a><\/strong> occurs when an organism is buried, and then <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1778\">elements<\/a> in groundwater completely impregnate all spaces within the body, even cells. Soft body structures can be preserved in great detail, but stronger materials like bone and teeth are the most likely to be preserved. Petrified wood is an example of detailed cellulose structures in the wood being preserved. The University of California Berkeley <a href=\"http:\/\/www.ucmp.berkeley.edu\/paleo\/fossils\/permin.html\">website<\/a> has more information on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1230\">permineralization<\/a>.<\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1232\">Molds<\/a><\/strong> and <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1231\">casts<\/a><\/strong> form when the original material of the organism dissolves and leaves a cavity in the surrounding rock. The shape of this cavity is an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1232\">external mold<\/a>. If the mold is subsequently filled with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a> or a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1785\">precipitate<\/a>, the organism\u2019s external shape is preserved as a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1231\">cast<\/a>. Sometimes internal cavities of organisms, such internal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1231\">casts<\/a> of clams, snails, and even skulls are preserved as internal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1231\">casts<\/a> showing details of soft structures. If the chemistry is right, and burial is rapid, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> nodules form around soft structures preserving the three-dimensional detail. This is called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1233\">authigenic mineralization<\/a><\/strong>.<\/p>\n<figure id=\"attachment_3254\" aria-describedby=\"caption-attachment-3254\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.21_external_mold_Aviculopecten_subcardiformis.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-499 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis-300x300.jpg\" alt=\"Photo of external mold of a clam shell\" width=\"300\" height=\"300\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis-300x300.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis-1024x1022.jpg 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis-150x150.jpg 150w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis-768x766.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis-65x65.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis-225x224.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis-350x349.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_external_mold_Aviculopecten_subcardiformis.jpg 1230w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3254\" class=\"wp-caption-text\">External mold of a clam<\/figcaption><\/figure>\n<figure id=\"attachment_3255\" aria-describedby=\"caption-attachment-3255\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.23_carbonization_of_ViburnumFossil.jpg\"><img decoding=\"async\" class=\"wp-image-500 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3255\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.23_carbonization_of_ViburnumFossil-300&#215;215.jpg\u00a0\u00bb alt=\u00a0\u00bbcarbonized leaf fossil showing insect damage and vein structure\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb215&Prime;&gt; Carbonized leaf<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1234\">Carbonization<\/a><\/strong> occurs when the organic tissues of an organism are compressed, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1684\">volatiles<\/a> are driven out, and everything but the carbon disappears leaving a carbon silhouette of the original organism. Leaf and fern <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> are examples of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1234\">carbonization<\/a><span style=\"font-weight: 400\">.<\/span><\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1235\">Trace fossils<\/a><\/strong> are indirect evidence left behind by an organism, such as burrows and footprints, as it lived its life. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1235\">Ichnology<\/a><\/strong> is specifically the study of prehistoric animal tracks. Dinosaur tracks testify to their presence and movement over an area, and even provide information about their size, gait, speed, and behavior. Burrows dug by tunneling organisms tell of their presence and mode of life. <span style=\"font-weight: 400\">Other <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1235\">trace fossils<\/a> include fossilized feces called <strong>coprolites<\/strong> and stomach stones called <strong>gastroliths<\/strong><\/span> that provide information about diet and habitat.<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3256\" aria-describedby=\"caption-attachment-3256\" style=\"width: 189px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.24_Cheirotherium_prints_possibly_Ticinosuchus.jpg\"><img decoding=\"async\" class=\"wp-image-501 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3256\" class=\"wp-caption-text\">Ballista<\/a> at the <a href=\"denied:&quot;https:\/\/en.wikipedia.org\/wiki\/&quot;\" class=\"&quot;extiw&quot;\" title=\"&quot;w:&quot;\">English language Wikipedia<\/a> [<a href=\"denied:&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ACheirotherium_prints_possibly_Ticinosuchus.JPG&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.24_Cheirotherium_prints_possibly_Ticinosuchus-189&#215;300.jpg\u00a0\u00bb alt=\u00a0\u00bbTracks of a smal1 dinosaur\u00a0\u00bb width=\u00a0\u00bb189&Prime; height=\u00a0\u00bb300&Prime;&gt; Foot prints of the early crocodile Chirotherium<\/figcaption><\/figure>\n<figure id=\"attachment_3257\" aria-describedby=\"caption-attachment-3257\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.26_Coprolite.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-502 size-medium\" title=\"USGS, public domain\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.26_Coprolite-300x200.jpg\" alt=\"fossilized animal droppings\" width=\"300\" height=\"200\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.26_Coprolite-300x200.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.26_Coprolite-1024x683.jpg 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.26_Coprolite-768x512.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.26_Coprolite-65x43.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.26_Coprolite-225x150.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.26_Coprolite-350x233.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.26_Coprolite.jpg 1536w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3257\" class=\"wp-caption-text\">Fossil animal droppings (coprolite)<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<h3><span style=\"font-weight: 400\">7.3.2 Evolution<\/span><\/h3>\n<p><strong>Evolution<\/strong> has created a variety of ancient <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> that are important to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1237\">stratigraphic correlation<\/a>. (see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/7-geologic-time\/\">chapter 7<\/a> and <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">Chapter 5<\/a>) This section is a brief discussion of the process of evolution. The British naturalist Charles Darwin (1809-1882) recognized that life forms evolve into progeny life forms. He proposed <strong>natural selection<\/strong>\u2014which operated on organisms living under environmental conditions that posed challenges to survival\u2014was the mechanism driving the process of evolution forward.<\/p>\n<figure id=\"attachment_3258\" aria-describedby=\"caption-attachment-3258\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.27_bell-shaped_curve.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-503 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.27_bell-shaped_curve-300x176.jpg\" alt=\"Berll-shaped curve showing how variation within a population is distributed with respect to characteristics. Most members group in the center with rarer members on the tails.\" width=\"300\" height=\"176\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.27_bell-shaped_curve-300x176.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.27_bell-shaped_curve-65x38.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.27_bell-shaped_curve-225x132.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.27_bell-shaped_curve-350x205.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.27_bell-shaped_curve.jpg 682w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3258\" class=\"wp-caption-text\">Variation within a population<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The basic classification unit of life is the <strong>species<\/strong>: a population of organisms that exhibit shared characteristics and are capable of reproducing fertile offspring. For a species to survive, each individual within a particular population is faced with challenges posed by the environment and must survive them long enough to reproduce. Within the natural variations present in the population, there may be individuals possessing characteristics that give them some advantage in facing the environmental challenges. These individuals are more likely to reproduce and pass these favored characteristics on to successive generations. If sufficient individuals in a population fail to surmount the challenges of the environment and the population cannot produce enough viable offspring, the species becomes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_755\">extinct<\/a>. The average lifespan of a species in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossil<\/a> record is around a million years. That life still exists on Earth shows the role and importance of evolution as a natural process in meeting the continual challenges posed by our dynamic Earth. If the inheritance of certain distinctive characteristics is sufficiently favored over time, populations may become genetically isolated from one another, eventually resulting in the evolution of separate species. This genetic isolation may also be caused by a geographic barrier, such as an island surrounded by ocean. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1733\">theory<\/a> of evolution by natural selection was elaborated by Darwin in his book <em>On the Origin of Species<\/em>\u00a0(see <a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/1-understanding-science\/\">Chapter 1<\/a>). <\/span>Since Darwin\u2019s original ideas, technology has provided many tools and mechanisms to study how evolution and speciation take place and this arsenal of tools is growing. Evolution is well beyond the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1730\">hypothesis<\/a> stage and is a well-established <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1733\">theory<\/a> of modern science.<\/p>\n<p>Variation within populations occurs by the natural mixing of genes through sexual reproduction or from naturally occurring mutations. Some of this genetic variation can introduce advantageous characteristics that increase the individual\u2019s chances of survival. While some species in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossil<\/a> record show little morphological change over time, others show gradual or punctuated changes, within which <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1007\">intermediate<\/a> forms can be seen.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-45\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-45\" class=\"h5p-iframe\" data-content-id=\"45\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"7.3 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4085\" aria-describedby=\"caption-attachment-4085\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/7.3-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-504\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.3-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4085\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 7.3 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\"> 7.4 Correlation<\/span><\/h2>\n<figure id=\"attachment_3259\" aria-describedby=\"caption-attachment-3259\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Wegener_fossil_map.svg_.png\"><img decoding=\"async\" class=\"wp-image-71 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3259\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Wegener_fossil_map.svg_-300&#215;231.png\u00a0\u00bb alt=\u00a0\u00bbThere are four different fossil organisms that connect South America, Africa, India, Antartica, and Australia.\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb231&Prime;&gt; Image showing fossils that connect the continents of Gondwana (the southern continents of Pangea).<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1236\">Correlation<\/a> is the process of establishing which sedimentary strata are of the same age but geographically separate. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1236\">Correlation<\/a> can be determined by using magnetic polarity reversals (<a href=\"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>), rock types, unique rock sequences, or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1241\">index fossils<\/a>. There are four main types of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1236\">correlation<\/a>: stratigraphic, lithostratigraphic, chronostratigraphic, and biostratigraphic.<\/p>\n<h3><strong>7.4.1 Stratigraphic Correlation<\/strong><\/h3>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1237\">Stratigraphic correlation<\/a><\/strong> is the process of establishing which sedimentary strata are the same age at distant geographical areas by means of their stratigraphic relationship. Geologists construct geologic histories of areas by mapping and making stratigraphic columns-a detailed description of the strata from bottom to top. An example of stratigraphic relationships and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1236\">correlation<\/a> between Canyonlands National Park and Zion National Park in Utah. At Canyonlands, the Navajo Sandstone overlies the Kayenta Formation which overlies the cliff-forming Wingate Formation. In Zion, the Navajo Sandstone overlies the Kayenta formation which overlies the cliff-forming Moenave Formation. Based on the stratigraphic relationship, the Wingate and Moenave Formations correlate. These two formations have unique names because their composition and outcrop pattern is slightly different.<span style=\"font-weight: 400\"> Other strata in the Colorado Plateau and their sequence can be recognized and correlated over thousands of square miles.<\/span><\/p>\n<figure id=\"attachment_3260\" aria-describedby=\"caption-attachment-3260\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.4_Grand_Staircase_Correlation.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-505 size-large\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation-1024x291.jpg\" alt=\"Cross-section showing the same strata in the Grand Canyon, Zion, Bryce Canyon, and Cedar Breaks\" width=\"1024\" height=\"291\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation-1024x291.jpg 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation-300x85.jpg 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation-768x218.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation-1536x436.jpg 1536w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation-65x18.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation-225x64.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation-350x99.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Grand_Staircase_Correlation.jpg 1700w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-3260\" class=\"wp-caption-text\">Correlation of strata along the Grand Staircase from the Grand Canyon to Zion Canyon, Bryce Canyon and Cedar Breaks. (Source: National Park Service)<\/figcaption><\/figure>\n<h3><strong>7.4.2 Lithostratigraphic Correlation<\/strong><\/h3>\n<figure id=\"attachment_3261\" aria-describedby=\"caption-attachment-3261\" style=\"width: 221px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.28_Navajo_Sandstone_Zion_angels_landing_view.jpg\"><img decoding=\"async\" class=\"wp-image-506\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3261\" class=\"wp-caption-text\">GFDL<\/a>, <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/2.5-2.0-1.0&quot;\">CC BY-SA 2.5-2.0-1.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AZion_angels_landing_view.jpg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.28_Navajo_Sandstone_Zion_angels_landing_view-293&#215;300.jpg\u00a0\u00bb alt=\u00a0\u00bbView of Navajo Sandstone from Angel&rsquo;s Landing in Zion National Park\u00a0\u00bb width=\u00a0\u00bb221&Prime; height=\u00a0\u00bb227&Prime;&gt; View of Navajo Sandstone from Angel&rsquo;s Landing in Zion&rsquo;s National Park<\/figcaption><\/figure>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1238\">Lithostratigraphic correlation<\/a><\/strong> establishes a similar age of strata based on the <strong>lithology<\/strong> that is the composition and physical properties of that strata.<em> Lithos<\/em> is Greek for stone and -logy comes from the Greek word for doctrine or science.\u00a0 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1238\">Lithostratigraphic correlation<\/a> can be used to correlate whole formations long distances or can be used to correlate smaller strata within formations to trace their extent and regional depositional environments.<\/p>\n<figure id=\"attachment_3262\" aria-describedby=\"caption-attachment-3262\" style=\"width: 232px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.29_Navajo_Sandstone_StevensArchUT.jpg\"><img decoding=\"async\" class=\"wp-image-507\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3262\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.29_Navajo_Sandstone_StevensArchUT-300&#215;212.jpg\u00a0\u00bb alt=\u00a0\u00bbStevens Arch in the Navajo Sandstone at Coyote Gulch some 125 miles away from Zions Park\u00a0\u00bb width=\u00a0\u00bb232&Prime; height=\u00a0\u00bb164&Prime;&gt; Stevens Arch in the Navajo Sandstone at Coyote Gulch some 125 miles away from Zions Park<\/figcaption><\/figure>\n<p>For example, the Navajo Sandstone, which makes up the prominent walls of Zion National Park, is the same Navajo Sandstone in Canyonlands because the lithology of the two are identical even though they are hundreds of miles apart. \u00a0Extensions of the same Navajo Sandstone formation are found miles away in other parts of southern Utah, including Capitol Reef and Arches National Parks. Further, this same formation is the called the Aztec Sandstone in Nevada and Nugget Sandstone near Salt Lake City because they are lithologically distinct enough to warrant new names.<\/p>\n<h3><strong>7.4.3 Chronostratigraphic Correlation<\/strong><\/h3>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1239\">Chronostratigraphic correlation<\/a><\/strong> matches rocks of the same age, even though they are made of different lithologies. Different lithologies of sedimentary rocks can form at the same time at different geographic locations because depositional environments vary geographically. For example, at any one time in a marine setting there could be this sequence of depositional environments from beach to deep marine: beach, near shore area, shallow marine lagoon, reef, slope, and deep marine. Each depositional environment will have a unique <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1761\">sedimentary rock<\/a> formation. On the figure of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_476\">Permian<\/a> Capitan Reef at Guadalupe National Monument in West Texas, the red line shows a chronostratigraphic time line that represents a snapshot in time. Shallow-water marine lagoon\/back reef area is light blue, the main Capitan reef is dark blue, and deep-water marine siltstone is yellow. All three of these unique lithologies were forming at the same time in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_476\">Permian<\/a> along this red timeline.<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3263\" aria-describedby=\"caption-attachment-3263\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.4_Chronostrat_Guadelupe_NM.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-508 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Chronostrat_Guadelupe_NM-300x184.png\" alt=\"Cross-section showing three different rocks strata with unique lithology all being deposited at the same ancient time in nearby geographic areas.\" width=\"300\" height=\"184\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Chronostrat_Guadelupe_NM-300x184.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Chronostrat_Guadelupe_NM-65x40.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Chronostrat_Guadelupe_NM-225x138.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.4_Chronostrat_Guadelupe_NM.png 326w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3263\" class=\"wp-caption-text\">Cross-section of the Permian El Capitan Reef at Guadalupe National Monument, Texas. The red line shows a chronostratigraphic time line that represents a snapshot in time in which the shallow marine lagoon\/back reef area (light blue), main Capitan reef (dark blue), and deep marine silstones (yellow) were all being deposited at the same time.<\/figcaption><\/figure>\n<figure id=\"attachment_3264\" aria-describedby=\"caption-attachment-3264\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/TransgressionRegression-1.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-410 size-medium\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/TransgressionRegression-1-300x199.png\" alt=\"Onlap is sediments moving toward the land. Offlap is moving away.\" width=\"300\" height=\"199\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/TransgressionRegression-1-300x199.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/TransgressionRegression-1-65x43.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/TransgressionRegression-1-225x149.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/TransgressionRegression-1-350x232.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/TransgressionRegression-1.png 500w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3264\" class=\"wp-caption-text\">The rising sea levels of transgressions create onlapping sediments, regressions create offlapping. Ocean water is shown in blue so the time line is on the surface below the water. At the same time sandstone (buff color), limestone (gray), and shale (mustard color) are all forming at different depths of water.<\/figcaption><\/figure>\n<h3><strong>7.4.4 Biostratigraphic Correlation<\/strong><\/h3>\n<figure id=\"attachment_3265\" aria-describedby=\"caption-attachment-3265\" style=\"width: 250px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.32_Conodonts_from_Alaska.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-509 size-medium\" title=\"USGS image, public domain\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.32_Conodonts_from_Alaska-250x300.jpg\" alt=\"Illustration of microscopic conodonts from Alaska showing several different plate and tooth-like forms\" width=\"250\" height=\"300\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.32_Conodonts_from_Alaska-250x300.jpg 250w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.32_Conodonts_from_Alaska-65x78.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.32_Conodonts_from_Alaska-225x270.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.32_Conodonts_from_Alaska-350x419.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.32_Conodonts_from_Alaska.jpg 484w\" sizes=\"auto, (max-width: 250px) 100vw, 250px\" \/><\/a><figcaption id=\"caption-attachment-3265\" class=\"wp-caption-text\">Conodonts<\/figcaption><\/figure>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1240\">Biostratigraphic correlation<\/a><\/strong> uses <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1241\">index fossils<\/a> to determine strata ages. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1241\">Index fossils<\/a> represent assemblages or groups of organisms that were uniquely present during specific intervals of geologic time. Assemblages is referring a group of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">Fossils<\/a> allow geologists to assign a formation to an absolute date range, such as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_486\">Jurassic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">Period<\/a> (199 to 145 million years ago), rather than a relative time scale. In fact, most of the geologic time ranges are mapped to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossil<\/a> assemblages. The most useful <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1241\">index fossils<\/a> come from lifeforms that were geographically widespread and had a species lifespan that was limited to a narrow time interval. In other words, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1241\">index fossils<\/a>\u00a0can be found in many places around the world, but only during a narrow time frame. Some of the best <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1240\">biostratigraphic correlation<\/a> are microfossils<strong>,<\/strong> most of which came from single-celled organisms. As with microscopic organisms today, they were widely distributed across many environments throughout the world. Some of these microscopic organisms had hard parts, such as exoskeletons or outer shells, making them better candidates for preservation. Foraminifera, single celled organisms with calcareous shells, are an example of an especially useful <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1241\">index fossil<\/a> for the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_487\">Cretaceous<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">Period<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_488\">Cenozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1243\">Era<\/a><span style=\"font-weight: 400\">.<\/span><\/p>\n<p><strong>Conodonts<\/strong> are another example of microfossils useful for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1240\">biostratigraphic correlation<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1276\">Cambrian<\/a> through <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_485\">Triassic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">Periods<\/a>. Conodonts are tooth-like phosphatic structures of an eel-like multi-celled organism that had no other preservable hard parts. The conodont-bearing creatures lived in shallow marine environments all over the world. Upon death, the phosphatic hard parts were scattered into the rest of the marine <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a>. These distinctive tooth-like structures are easily collected and separated from limestone in the laboratory.<\/p>\n<figure id=\"attachment_3266\" aria-describedby=\"caption-attachment-3266\" style=\"width: 380px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.21_index_fossils.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-510\" title=\"USGS image\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_index_fossils-300x237.gif\" alt=\"Image showing index fossils that identify ages of the Geologic Time Scale\" width=\"380\" height=\"300\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_index_fossils-300x237.gif 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_index_fossils-65x51.gif 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_index_fossils-225x178.gif 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.21_index_fossils-350x276.gif 350w\" sizes=\"auto, (max-width: 380px) 100vw, 380px\" \/><\/a><figcaption id=\"caption-attachment-3266\" class=\"wp-caption-text\">Index fossils used for biostratigraphic correlation<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3267\" aria-describedby=\"caption-attachment-3267\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.31_foraminifera_Quinqueloculina_seminula-scaled.jpg\"><img decoding=\"async\" class=\"wp-image-3267 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3267\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.31_foraminifera_Quinqueloculina_seminula-scaled-1.jpg\u00a0\u00bb alt=\u00a0\u00bbSpecimens of faraminifera, a microfossil with a hard shell\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb225&Prime;&gt; Foraminifera, microscopic creatures with hard shells<\/figcaption><\/figure>\n<figure id=\"attachment_3268\" aria-describedby=\"caption-attachment-3268\" style=\"width: 299px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.33_Euconodonta.gif\"><img decoding=\"async\" class=\"wp-image-512 size-full\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3268\" class=\"wp-caption-text\">CC BY 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AEuconodonta.gif&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Euconodonta.gif\u00a0\u00bb alt=\u00a0\u00bbArtists rendering of what the conodont anmal might have looked like, an eel-like creature with large eyes and an apparatus of conodonts as mouthparts.\u00a0\u00bb width=\u00a0\u00bb299&Prime; height=\u00a0\u00bb234&Prime;&gt; Artist reconstruction of the conodont animal<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\">Because the conodont creatures were so widely abundant, rapidly evolving, and readily preserved in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1756\">sediments<\/a>, their <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> are especially useful for correlating strata, even though knowledge of the actual animal possessing them is sparse. Scientists in the 1960s carried out a fundamental <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1240\">biostratigraphic correlation<\/a> that tied <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_485\">Triassic<\/a> conodont zonation into ammonoids, which are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_755\">extinct<\/a> ancient cousins of the pearly nautilus. Up to that point ammonoids were the only standard for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_485\">Triassic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1236\">correlation<\/a>, so cross-referencing micro- and macro-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1241\">index fossils<\/a> enhanced the reliability of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1240\">biostratigraphic correlation<\/a> for either type<\/span><span style=\"font-weight: 400\">. <\/span>That conodont study went on to establish the use of conodonts to internationally correlate <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_485\">Triassic<\/a> strata located in Europe, Western North America, and the Arctic Islands of Canada<span style=\"font-weight: 400\">.\u00a0<\/span><\/p>\n<h3><span style=\"font-weight: 400\">7.4.5 Geologic Time Scale<\/span><\/h3>\n<figure id=\"attachment_2486\" aria-describedby=\"caption-attachment-2486\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/GeologicClock.png\"><img decoding=\"async\" class=\"wp-image-52 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-2486\" class=\"wp-caption-text\">By WoudloperDerivative work: Hardwigg (File:Geologic_clock.jpg) [Public domain], <\/a><a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AGeologic_Clock_with_events_and_periods.svg&quot;\">via Wikimedia Commons<\/a>\u00a0\u00bb src=\u00a0\u00bbhttps:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/GeologicClock-300&#215;288.png\u00a0\u00bb alt=\u00a0\u00bbThe circle starts at 4.6 billion years ago, then loops around to zero.\u00a0\u00bb width=\u00a0\u00bb300&Prime; height=\u00a0\u00bb288&Prime;&gt; Geologic time on Earth, represented circularly, to show the individual time divisions and important events. Ga=billion years ago, Ma=million years ago.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p>Geologic time has been subdivided into a series of divisions by geologists. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1242\">Eon<\/a> is the largest division of time, followed by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1243\">era<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">period<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1245\">epoch<\/a>, and age. The partitions of the geologic time scale is the same everywhere on Earth; however, rocks may or may not be present at a given location depending on the geologic activity going on during a particular <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">period<\/a> of time. Thus, we have the concept of time vs. rock, in which time is an unbroken continuum but rocks may be missing and\/or unavailable for study. The figure of the geologic time scale, represents time flowing continuously from the beginning of the Earth, with the time units presented in an unbroken sequence. But that does not mean there are rocks available for study for all of these time units.<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_2487\" aria-describedby=\"caption-attachment-2487\" style=\"width: 793px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/17.18_Geologic_Time_Scale_with_years-1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-53 size-large\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/17.18_Geologic_Time_Scale_with_years-1-793x1024.jpg\" alt=\"The Geologic Time Scale with an age of each unit shown by a scale\" width=\"793\" height=\"1024\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/17.18_Geologic_Time_Scale_with_years-1-793x1024.jpg 793w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/17.18_Geologic_Time_Scale_with_years-1-232x300.jpg 232w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/17.18_Geologic_Time_Scale_with_years-1-768x992.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/17.18_Geologic_Time_Scale_with_years-1-65x84.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/17.18_Geologic_Time_Scale_with_years-1-225x291.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/17.18_Geologic_Time_Scale_with_years-1-350x452.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/17.18_Geologic_Time_Scale_with_years-1.jpg 854w\" sizes=\"auto, (max-width: 793px) 100vw, 793px\" \/><\/a><figcaption id=\"caption-attachment-2487\" class=\"wp-caption-text\">Geologic Time Scale with ages shown<\/figcaption><\/figure>\n<figure id=\"attachment_3271\" aria-describedby=\"caption-attachment-3271\" style=\"width: 207px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/07.33_Geologic_time_scale_of_earth.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-513\" title=\"1888-1889, Popular Science Monthly Volume 34 (public domain)\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-373x1024.jpg\" alt=\"Stylized column of rock strata related to the eras and periods of the Geologic Time Scale illustrating the association of time, rock, and earth history\" width=\"207\" height=\"568\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-373x1024.jpg 373w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-109x300.jpg 109w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-768x2107.jpg 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-560x1536.jpg 560w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-746x2048.jpg 746w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-65x178.jpg 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-225x617.jpg 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth-350x960.jpg 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/07.33_Geologic_time_scale_of_earth.jpg 789w\" sizes=\"auto, (max-width: 207px) 100vw, 207px\" \/><\/a><figcaption id=\"caption-attachment-3271\" class=\"wp-caption-text\">Names from the Geologic Time Scale applied to strata in a region<\/figcaption><\/figure>\n<p>The geologic time scale was developed during the 19<sup>th<\/sup> century using the principles of stratigraphy. The relative order of the time units was determined before geologist had the tools to assign numerical ages to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">periods<\/a> and events. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1240\">Biostratigraphic correlation<\/a> using <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> to assign <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1243\">era<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">period<\/a> names to sedimentary rocks on a worldwide scale<span style=\"font-weight: 400\">. <\/span><span style=\"font-weight: 400\">With the expansion of science and technology, some geologists think the influence of humanity on natural processes has become so great they are suggesting a new geologic time <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">period<\/a>, known as the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_489\">Anthropocene<\/a><\/strong>.<\/span><span style=\"font-weight: 400\"><br \/>\n<\/span><\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-46\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-46\" class=\"h5p-iframe\" data-content-id=\"46\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"7.4 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4086\" aria-describedby=\"caption-attachment-4086\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/7.4-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-514\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/7.4-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4086\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 7.4 via this QR Code.<\/figcaption><\/figure>\n<h2>Chapter summary<\/h2>\n<p>Events in Earth history can be placed in sequence using the five principles of relative dating. The geologic time scale was completely worked out in the 19th Century using these principles without knowing any actual numeric ages for the events. The discovery of radioactivity in the late 1800s enabled absolute dating, the assignment of numerical ages to events in the Earth\u2019s history, using decay of unstable radioactive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotopes<\/a>. Accurately interpreting radioisotopic dating data depends on the type of rock tested and accurate assumptions about <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1779\">isotope<\/a> baseline values. With a combination of relative and absolute dating, the history of geological events, age of Earth, and a geologic time scale have been determined with considerable accuracy. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1237\">Stratigraphic correlation<\/a> is additional tool used for understanding how depositional environments change geographically. Geologic time is vast, providing plenty of time for the evolution of various lifeforms, and some of these have become preserved as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> that can be used for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1240\">biostratigraphic correlation<\/a>. The geologic time scale is continuous, although the rock record may be broken because rocks representing certain time <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1244\">periods<\/a> may be missing.<\/p>\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n<div id=\"h5p-47\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-47\" class=\"h5p-iframe\" data-content-id=\"47\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Chapter 7 Review\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4087\" aria-describedby=\"caption-attachment-4087\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Ch.-7-Review-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-515\" src=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code-150x150.png 150w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code-300x300.png 300w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code-1024x1024.png 1024w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code-768x768.png 768w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code-65x65.png 65w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code-225x225.png 225w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code-350x350.png 350w, https:\/\/integrations.pressbooks.network\/app\/uploads\/sites\/516\/2022\/05\/Ch.-7-Review-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4087\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the review quiz for Chapter 7 via this QR Code.<\/figcaption><\/figure>\n<h1><span style=\"font-weight: 400\">References<\/span><\/h1>\n<div class=\"csl-bib-body\">\n<ol>\n<li class=\"csl-entry\">Allison, P.A., and Briggs, D.E.G., 1993, Exceptional <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossil<\/a> record: Distribution of soft-tissue preservation through the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1269\">Phanerozoic<\/a>: Geology, v. 21, no. 6, p. 527\u2013530.<\/li>\n<li class=\"csl-entry\">Bell, E.A., Boehnke, P., Harrison, T.M., and Mao, W.L., 2015, Potentially biogenic carbon preserved in a 4.1 billion-year-old <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircon<\/a>: Proc. Natl. Acad. Sci. U. S. A., v. 112, no. 47, p. 14518\u201314521.<\/li>\n<li class=\"csl-entry\">Brent Dalrymple, G., 1994, The Age of the Earth: Stanford University Press.<\/li>\n<li class=\"csl-entry\">Burleigh, R., 1981, W. F. Libby and the development of radiocarbon dating: Antiquity, v. 55, no. 214, p. 96\u201398.<\/li>\n<li class=\"csl-entry\">Christopher B. DuRoss, Stephen F. Personius, Anthony J. Crone, Susan S. Olig, and William R. Lund, 2011, Integration of Paleoseismic Data from Multiple Sites to Develop an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1722\">Objective<\/a> Earthquake Chronology: Application to the Weber Segment of the Wasatch Fault Zone, Utah: Bulletin of the Seismological Society of America, v. 101, no. 6, p. 2765\u20132781., doi: <a href=\"https:\/\/doi.org\/0.1785\/0120110102\">0.1785\/0120110102<\/a>.<\/li>\n<li class=\"csl-entry\">Dass, C., 2007, Basics of mass spectrometry, <i>in<\/i> Fundamentals of Contemporary Mass Spectrometry: John Wiley &amp; Sons, Inc., p. 1\u201314.<\/li>\n<li class=\"csl-entry\">Elston, D.P., Billingsley, G.H., and Young, R.A., 1989, Geology of Grand Canyon, Northern Arizona (with Colorado River Guides): Lees Ferry to Pierce Ferry, Arizona: Amer Geophysical Union.<\/li>\n<li class=\"csl-entry\">Erickson, J., Coates, D.R., and Erickson, H.P., 2014, An introduction to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1228\">fossils<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">minerals<\/a>: seeking clues to the Earth\u2019s past: Facts on File science library, Facts On File, Incorporated, Facts on File science library.<\/li>\n<li class=\"csl-entry\">Geyh, M.A., and Schleicher, H., 1990, Absolute Age Determination: Physical and Chemical Dating Methods and Their Application, 503 pp: Spring-er-Verlag, New York.<\/li>\n<li class=\"csl-entry\">Ireland, T., 1999, New tools for isotopic analysis: Science, v. 286, no. 5448, p. 2289\u20132290.<\/li>\n<li class=\"csl-entry\">Jackson, P.W., and of London, G.S., 2007, Four Centuries of Geological Travel: The Search for Knowledge on Foot, Bicycle, Sledge and Camel: Geological Society special publication, Geological Society, Geological Society special publication.<\/li>\n<li class=\"csl-entry\">Jaffey, A.H., Flynn, K.F., Glendenin, L.E., Bentley, W.C., and others, 1971, Precision measurement of half-lives and specific activities of U 235 and U 238: Phys. Rev. C Nucl. Phys.<\/li>\n<li class=\"csl-entry\">L\u00e9ost, I., F\u00e9raud, G., Blanc-Valleron, M.M., and Rouchy, J.M., 2001, First absolute dating of Miocene Langbeinite evaporites by 40Ar\/39Ar laser step-heating:[K2Mg2 (SO4) 3] Stebnyk Mine (Carpathian Foredeep <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_508\">Basin<\/a>): Geophys. Res. Lett., v. 28, no. 23, p. 4347\u20134350.<\/li>\n<li class=\"csl-entry\">Mosher, L.C., 1968, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_485\">Triassic<\/a> conodonts from Western North America and Europe and Their <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1236\">Correlation<\/a>: J. Paleontol., v. 42, no. 4, p. 895\u2013946.<\/li>\n<li class=\"csl-entry\">Oberth\u00fcr, T., Davis, D.W., Blenkinsop, T.G., and H\u00f6hndorf, A., 2002, Precise U\u2013Pb <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1765\">mineral<\/a> ages, Rb\u2013Sr and Sm\u2013Nd systematics for the Great Dyke, Zimbabwe\u2014constraints on late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1257\">Archean<\/a> events in the Zimbabwe <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1718\">craton<\/a> and Limpopo belt: <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1270\">Precambrian<\/a> Res., v. 113, no. 3\u20134, p. 293\u2013305.<\/li>\n<li class=\"csl-entry\">Patterson, C., 1956, Age of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1254\">meteorites<\/a> and the earth: Geochim. Cosmochim. Acta, v. 10, no. 4, p. 230\u2013237.<\/li>\n<li class=\"csl-entry\">Schweitzer, M.H., Wittmeyer, J.L., Horner, J.R., and Toporski, J.K., 2005, Soft-tissue vessels and cellular preservation in Tyrannosaurus rex: Science, v. 307, no. 5717, p. 1952\u20131955.<\/li>\n<li class=\"csl-entry\">Valley, J.W., Peck, W.H., King, E.M., and Wilde, S.A., 2002, A cool early Earth: Geology, v. 30, no. 4, p. 351\u2013354.<\/li>\n<li class=\"csl-entry\">Whewell, W., 1837, History of the Inductive Sciences: From the Earliest to the Present Times: J.W. Parker, 492 p.<\/li>\n<li class=\"csl-entry\">Wilde, S.A., Valley, J.W., Peck, W.H., and Graham, C.M., 2001, Evidence from detrital <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_516_1227\">zircons<\/a> for the existence of continental crust and oceans on the Earth 4.4 Gyr ago: Nature, v. 409, no. 6817, p. 175\u2013178.<\/li>\n<li class=\"csl-entry\">Winchester, S., 2009, The Map That Changed the World: William Smith and the Birth of Modern Geology: HarperCollins.<\/li>\n<\/ol>\n<\/div>\n<p><span style=\"font-weight: 400\">\u00a0<\/span><\/p>\n<div class=\"media-attributions clear\" prefix:cc=\"http:\/\/creativecommons.org\/ns#\" prefix:dc=\"http:\/\/purl.org\/dc\/terms\/\"><h2>Mention de la source du contenu multim\u00e9dia<\/h2><ul><li >Portrait_of_Nicolas_Stenonus       <\/li><li >Geologic_time_scale       <\/li><li >IsfjordenSuperposition       <\/li><li >lateral_continuity_Grandview_Point_Grand_Canyon_April_1995       <\/li><li >Faunal_sucession       <\/li><li >Stratigraphy_of_the_Grand_Canyon       <\/li><li >Redwall,_Temple_Butte_and_Muav_formations_in_Grand_Canyon       <\/li><li >Disconformity       <\/li><li >Nonconformity       <\/li><li >Angular unconformity       <\/li><li >7.1 Did I Get It QR Code       <\/li><li >Nuvvuagittuq_belt_rocks       <\/li><li >Isotopes of hydrogen       <\/li><li >Granite vs Gneiss       <\/li><li >Alpha_Decay.svg       <\/li><li >U-238 decay chain       <\/li><li >Mass_spectrometer       <\/li><li >Carbon_Dioxide_400kyr       <\/li><li >Zircon_microscope       <\/li><li >Yellowstone volcano-ash beds       <\/li><li >7.2 Did I Get It QR Code       <\/li><li >external_mold_Aviculopecten_subcardiformis       <\/li><li >Coprolite       <\/li><li >bell-shaped_curve       <\/li><li >7.3 Did I Get It QR Code       <\/li><li >Grand_Staircase_Correlation       <\/li><li >Chronostrat_Guadelupe_NM       <\/li><li >TransgressionRegression       <\/li><li >Conodonts_from_Alaska       <\/li><li >index_fossils       <\/li><li >17.18_Geologic_Time_Scale_with_years       <\/li><li >Geologic_time_scale_of_earth       <\/li><li >7.4 Did I Get It QR Code       <\/li><li >Ch. 7 Review QR Code       <\/li><\/ul><\/div><div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">d\u00e9finition<\/span><template id=\"term_516_1937\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1937\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2031\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2031\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1779\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1779\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2046\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2046\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1223\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1223\"><div tabindex=\"-1\"><p>Organic rich material found in soil.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1225\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1225\"><div tabindex=\"-1\"><p>Specific layers within a soil profile with specific properties.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2044\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2044\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1745\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1745\"><div tabindex=\"-1\"><p>Rocks which allow petroleum resources to collect or move.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1228\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1228\"><div tabindex=\"-1\"><p>Lowest layer of the soil (C), which is mechanically weathered (not chemically weathered) bedrock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1237\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1237\"><div tabindex=\"-1\"><p>A sedimentary rock with rounded, larger (\u22652 mm) clasts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1242\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1242\"><div tabindex=\"-1\"><p>Extremely thin bedding in mudstones, a characteristic of shale.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1243\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1243\"><div tabindex=\"-1\"><p>A very fine-grained rock with very thin layering (fissile).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1244\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1244\"><div tabindex=\"-1\"><p>A rock made of primarily silt.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1239\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1239\"><div tabindex=\"-1\"><p>A sandstone with a significant mud component OR a sandstone with a significant lithic fragment component.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1238\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1238\"><div tabindex=\"-1\"><p>A rock primarily made of sand.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1935\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1935\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1934\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1934\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2402\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2402\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1736\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1736\"><div tabindex=\"-1\"><p>Material found around ore which is less valuable and needs to be removed in order to obtain ore.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2032\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2032\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2033\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2033\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1756\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1756\"><div tabindex=\"-1\"><p>Carbonate rock that reacts with hot magmatic fluids, creating concentrated ore deposits, which include copper, iron, zinc, and gold.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1751\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1751\"><div tabindex=\"-1\"><p>Metallic mineral deposit consisting of mafic plutonic rocks, typically containing platinum-group elements, chromium, copper, nickel, etc.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_508\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_508\"><div tabindex=\"-1\"><p>(Source: National Park Service modified after Garber et al. 1989)<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2034\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2034\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_228\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_228\"><div tabindex=\"-1\"><p>QR Code generated with QRCode Monkey. All generated QR Codes are 100% free and can be used for whatever you want. This includes all commercial purposes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2035\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2035\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_495\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_495\"><div tabindex=\"-1\"><p>QR Code generated with QRCode Monkey. All generated QR Codes are 100% free and can be used for whatever you want. This includes all commercial purposes. <\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_502\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_502\"><div tabindex=\"-1\"><p>USGS, Public domain<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2143\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2143\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1753\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1753\"><div tabindex=\"-1\"><p>Metallic mineral deposit which forms near mid-ocean ridges.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2038\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2038\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2036\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2036\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1912\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1912\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2212\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2212\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1992\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1992\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2007\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2007\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1014\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1014\"><div tabindex=\"-1\"><p>Area behind the arc, which can be subject to compressional (causing thrusted mountain belts) or extensional (causing back-arc basins) forces.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1757\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1757\"><div tabindex=\"-1\"><p>Low grade, broad deposits of microscopic gold found in sedimentary rocks with diagenetic alteration.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1023\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1023\"><div tabindex=\"-1\"><p>Place where oceanic-oceanic subduction causes volcanoes to form on an overriding oceanic plate, making a chain of active volcanoes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1755\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1755\"><div tabindex=\"-1\"><p>Oxidation that occurs in sulfide deposits which can concentrate valuable elements like copper.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2039\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2039\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2040\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2040\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2041\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2041\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2042\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2042\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1761\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1761\"><div tabindex=\"-1\"><p>A highly weathered soil deposit that consists of aluminum ores.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1961\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1961\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1972\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1972\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1973\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1973\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1269\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1269\"><div tabindex=\"-1\"><p>A specific type of sedimentary structure (ripples, plane beds, etc.) linked to a specific flow regime.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1654\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1654\"><div tabindex=\"-1\"><p>Rock with abraded surfaces formed in deserts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1762\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1762\"><div tabindex=\"-1\"><p>Deposit of heavy ores in stream or beach sediments.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2010\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2010\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1020\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1020\"><div tabindex=\"-1\"><p>Where an ocean plate subducts beneath a continental plate, causing a volcanic arc to form.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1750\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1750\"><div tabindex=\"-1\"><p>Minerals that have a luster that is not similar to metal, and typically do not contain valuable metals like copper, lead, zinc, tin, etc.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1021\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1021\"><div tabindex=\"-1\"><p>Place with a chain of mountain volcanism on a continent, from oceanic-continental subduction.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2185\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2185\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1908\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1908\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1765\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1765\"><div tabindex=\"-1\"><p>A rule that says the outer valence shell of electrons is complete when it contains 8 electrons.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2043\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2043\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2158\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2158\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1778\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1778\"><div tabindex=\"-1\"><p>[glossary]<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2045\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2045\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1742\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1742\"><div tabindex=\"-1\"><p>A dark liquid fossil fuel derived from petroleum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1752\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1752\"><div tabindex=\"-1\"><p>An ultramafic rock from deep volcanic vents that can contain diamonds.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2441\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2441\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1766\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1766\"><div tabindex=\"-1\"><p>Minerals with the same composition and different crystal structures<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1785\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1785\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1920\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1920\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1004\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1004\"><div tabindex=\"-1\"><p>Place where two plates come together, casing subduction or collision.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1022\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1022\"><div tabindex=\"-1\"><p>Where a dense ocean plate subducts beneath a less dense oceanic&nbsp;plate, causing an island arc to form.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1227\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1227\"><div tabindex=\"-1\"><p>Lower layer of the soil (B) which is a mixture of weathered bedrock, leeched materials, and organic material. Has two sublayers: the upper part, or regolith (with more organic materials), and the lower part, saprolite, which is only slightly weathered bedrock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2418\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2418\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1222\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1222\"><div tabindex=\"-1\"><p>Certain metallic elements (like iron) take in oxygen, causing reactions like rust.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2047\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2047\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1254\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1254\"><div tabindex=\"-1\"><p>Chemical sedimentary rocks that have a biologic component to their origin. Many limestones are biochemical.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1253\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1253\"><div tabindex=\"-1\"><p>A very fine grained version of silica deposited with or without microfossils.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_4207\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_4207\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1224\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1224\"><div tabindex=\"-1\"><p>A hypothetical or real section cut through soil, showing the different layers (horizons) that exist.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2449\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2449\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1226\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1226\"><div tabindex=\"-1\"><p>Upper layer of soil, made mainly out of organic material.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_500\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_500\"><div tabindex=\"-1\"><p>By Wilson44691 (Own work) [Public domain], <a href=\"https:\/\/commons.wikimedia.org\/wiki\/File%3AViburnumFossil.jpg\">via Wikimedia Commons<\/a><\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1698\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1698\"><div tabindex=\"-1\"><p>Ridge of sediment that forms under a glacier by meltwater which forms a river.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1781\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1781\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1655\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1655\"><div tabindex=\"-1\"><p>A depression in dune sediment formed because of a lack of anchoring vegetation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1664\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1664\"><div tabindex=\"-1\"><p>Dunes that form semicircular shapes due to anchoring vegetation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1754\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1754\"><div tabindex=\"-1\"><p>Large metallic mineral deposit that forms near magma bodies like plutons. Commonly contains copper, lead, zinc, molybdenum, and gold.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1001\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1001\"><div tabindex=\"-1\"><p>A boundary between continental and oceanic plates that has relative movement, making it a plate boundary.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1936\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1936\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1787\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1787\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_967\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_967\"><div tabindex=\"-1\"><p>By Hermann Luyken (Own work) [<a href=\"http:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en\">CC0<\/a>], <a href=\"https:\/\/commons.wikimedia.org\/wiki\/File%3A2012.10.02.111543_Bonneville_Salt_Flats_Utah.jpg\">via Wikimedia Commons<\/a><\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2182\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2182\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_250\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_250\"><div tabindex=\"-1\"><p>By Amcyrus2012 (Own work) [<a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\">CC BY 4.0<\/a>], <a href=\"https:\/\/commons.wikimedia.org\/wiki\/File%3ADiorite_MA.JPG\">via Wikimedia Commons<\/a><\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1231\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1231\"><div tabindex=\"-1\"><p>Changes in sedimentary rocks due to increased (but low when compared to metamorphism) temperatures and pressures. This can include deposition of new minerals (e.g. limestone converting to dolomite) or dissolution of existing minerals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1232\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1232\"><div tabindex=\"-1\"><p>The average diameter of a grain of sediment, ranging from small, also known as fine-grained (e.g. clay, silt) to large, also known as coarse-grained (e.g. boulder).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1893\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1893\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1980\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1980\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2037\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2037\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1229\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1229\"><div tabindex=\"-1\"><p>Sedimentary rocks that are made of sediment, weathered pieces of bedrock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1230\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1230\"><div tabindex=\"-1\"><p>Sedimentary rocks that are precipitated, from solution.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1234\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1234\"><div tabindex=\"-1\"><p>How smooth or rough the edges are within a sediment.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1235\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1235\"><div tabindex=\"-1\"><p>The mineral make up of a rock, i.e. which minerals are found within a rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1988\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1988\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2207\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2207\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1233\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1233\"><div tabindex=\"-1\"><p>The range of sediment sizes within a sediment or sediment within sedimentary rocks. Well sorted means the sediment has the same sizes, poorly sorted means many different sizes are present.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1684\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1684\"><div tabindex=\"-1\"><p>Low point within an&nbsp;ar\u00eate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_755\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_755\"><div tabindex=\"-1\"><p>QR Code generated with QRCode Monkey. All generated QR Codes are 100% free and can be used for whatever you want. This includes all commercial purposes. <\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1733\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1733\"><div tabindex=\"-1\"><p>Large surface mine with opening carved into the ground.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1730\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1730\"><div tabindex=\"-1\"><p>Potentially extractible and valuable material, but unproven.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1007\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1007\"><div tabindex=\"-1\"><p>Deepest part of the ocean where a subducting plate dives below the overriding plate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1236\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1236\"><div tabindex=\"-1\"><p>The study of the components of a rock, mainly sedimentary rocks, and the information that can be obtained by understanding the origin of the components.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1241\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1241\"><div tabindex=\"-1\"><p>A rock made of primarily mud, i.e. particles smaller than sand (\u22640.064 mm).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1909\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1909\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1960\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1960\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1976\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1976\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2273\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2273\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1978\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1978\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_476\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_476\"><div tabindex=\"-1\"><p>By \u05d3\u05e7\u05d9 [<a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\">CC BY-SA 3.0<\/a> or <a href=\"http:\/\/www.gnu.org\/copyleft\/fdl.html\">GFDL<\/a>], <a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Nonconformity.jpg\">from Wikimedia Commons<\/a><\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1918\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1918\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1240\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1240\"><div tabindex=\"-1\"><p>A sandstone rich in feldspar.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_486\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_486\"><div tabindex=\"-1\"><p>By Pamputt (Own work) [<a href=\"http:\/\/creativecommons.org\/licenses\/by-sa\/4.0\">CC BY-SA 4.0<\/a>], <a href=\"https:\/\/commons.wikimedia.org\/wiki\/File%3AAtomic_rearrangement_following_an_electron_capture.svg\">via Wikimedia Commons<\/a><\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_487\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_487\"><div tabindex=\"-1\"><p>This is a copyrighted image from the CAMECA Archives<br \/>\nReproduction is authorized, under the terms of the GNU Free Documentation License.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_488\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_488\"><div tabindex=\"-1\"><p>By Krishnavedala (Own work) [<a href=\"http:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en\">CC0<\/a>], <a href=\"https:\/\/commons.wikimedia.org\/wiki\/File%3AHalf_times.svg\">via Wikimedia Commons<\/a><\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1276\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1276\"><div tabindex=\"-1\"><p>Similar to dunes, in that they are ridges of sand that form perpendicular to flow, but internally, the sediments dip up stream. Forms in the upper part of the upper flow regime.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_485\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_485\"><div tabindex=\"-1\"><p>By ThaLibster [<a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\">CC BY-SA 4.0<\/a>], <a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Decay_Chain_of_Uranium-238.svg\">from Wikimedia Commons<\/a><\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1929\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1929\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1245\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1245\"><div tabindex=\"-1\"><p>A rock made primarily of clay.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_489\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_489\"><div tabindex=\"-1\"><p>By Mike Christie (Own work) [<a href=\"http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\">CC BY-SA 3.0<\/a>], <a href=\"https:\/\/commons.wikimedia.org\/wiki\/File%3AAccelerator_mass_spectrometer_schematic_for_radiocarbon.svg\">via Wikimedia Commons<\/a><\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1722\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1722\"><div tabindex=\"-1\"><p>Data which is out of the ordinary and does not fit previous trends.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_2252\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_2252\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1257\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1257\"><div tabindex=\"-1\"><p>Limestone made of primarily fine-grained calcite mud. Microscopic fossils are commonly present.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1718\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1718\"><div tabindex=\"-1\"><p>A system which reverts back to a baseline when it deviates.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><template id=\"term_516_1270\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_516_1270\"><div tabindex=\"-1\"><p>A specific layer of rock formed by flowing fluid, either in the lowest part of the lower flow regime or lower part of the upper flow regime.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Fermer la d\u00e9finition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":291,"menu_order":7,"template":"","meta":{"pb_show_title":"","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[49],"contributor":[],"license":[],"class_list":["post-516","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":19,"_links":{"self":[{"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/pressbooks\/v2\/chapters\/516","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/wp\/v2\/users\/291"}],"version-history":[{"count":2,"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/pressbooks\/v2\/chapters\/516\/revisions"}],"predecessor-version":[{"id":1796,"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/pressbooks\/v2\/chapters\/516\/revisions\/1796"}],"part":[{"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/pressbooks\/v2\/parts\/19"}],"metadata":[{"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/pressbooks\/v2\/chapters\/516\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/wp\/v2\/media?parent=516"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/pressbooks\/v2\/chapter-type?post=516"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/wp\/v2\/contributor?post=516"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/integrations.pressbooks.network\/testcloneglossaryterms\/wp-json\/wp\/v2\/license?post=516"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}