Editing Grand Canyon (section)

==Geology==
{{Main|Geology of the Grand Canyon area}}
[[File:2021 Revised NPS Geologic Stratigraphic Column of the Grand Canyon.jpg|thumb|upright=1.4|Diagram showing the placement, age and thickness of the rock units exposed in the Grand Canyon]]
[[Image:GCRockfall.JPG|thumb|Rockfalls in recent times, along with other [[mass wasting]], have further widened the canyon]]

The Grand Canyon is part of the Colorado River basin, which has developed over the past 70{{nbsp}}million years.<ref name="Witze"/><ref>{{cite Q|Q56082876}}</ref> For more than 150 years, scientists have gathered data, proposed new ideas, and debated sometimes contentious theories about the geologic origins of the Grand Canyon and the Colorado River. Formation of the Grand Canyon and the Colorado River may involve a complex history in which multiple factors and geologic processes have interacted over time and in different locations.<ref name="Ranney"/>

In the most recent round of "old river" vs. "young river" controversy, researchers have challenged estimates that had placed the age of the canyon at 5–6{{nbsp}}million years. The research has aroused considerable controversy because it suggests a substantial departure from prior widely supported scientific consensus.<ref name="Johnson1">{{cite web |first1=Joshua |last1=Johnson |date=2013 |title=Western U.S. Tectonics: The Origin of the Grand Canyon – Controversy and Tectonic Implications – Intro page |url=http://cires1.colorado.edu/people/jones.craig/WUStectonics/grand_canyon/ |website=cires1.colorado.edu |access-date=June 23, 2022 |archive-date=February 13, 2023 |archive-url=https://web.archive.org/web/20230213100719/http://cires1.colorado.edu/people/jones.craig/WUStectonics/grand_canyon/ |url-status=live }}</ref><ref name="Johnson2">{{cite web |first1=Joshua |last1=Johnson |date=2013 |title=Western U.S. Tectonics: The Origin of the Grand Canyon – Controversy and Tectonic Implications – SYNTHESIS AND TECTONIC IMPLICATIONS |url=http://cires1.colorado.edu/people/jones.craig/WUStectonics/grand_canyon/ |website=cires1.colorado.edu |access-date=June 23, 2022 |archive-date=February 13, 2023 |archive-url=https://web.archive.org/web/20230213100719/http://cires1.colorado.edu/people/jones.craig/WUStectonics/grand_canyon/ |url-status=live }}</ref><ref name="Witze"/>

In a 2008 study, Victor Polyak examined caves near the Grand Canyon and placed their origins about 17{{nbsp}}million years ago. The study, which was published in the journal ''[[Science (journal)|Science]]'' in 2008, used [[uranium-lead dating]] to analyze [[calcite]] deposits found on the walls of nine caves throughout the canyon.<ref name="UNM Study">{{cite news |last=Wilford |first=John |title=Study Says Grand Canyon Older Than Thought |newspaper=New York Times |date=February 6, 2008 |url=https://www.nytimes.com/2008/03/06/science/06cnd-canyon.html?_r=2&hp&oref=slogin&oref=slogin |access-date=February 6, 2008 |url-status=live |archive-url=https://web.archive.org/web/20130517190314/http://www.nytimes.com/2008/03/06/science/06cnd-canyon.html?_r=2&hp&oref=slogin&oref=slogin |archive-date=May 17, 2013 }}</ref><ref name="NPR2008">{{cite news |title=How Old Is the Grand Canyon? |url=https://www.npr.org/2008/03/07/87984356/how-old-is-the-grand-canyon |access-date=June 23, 2022 |work=NPR.org |date=March 7, 2008 |language=en |archive-date=June 23, 2022 |archive-url=https://web.archive.org/web/20220623172907/https://www.npr.org/2008/03/07/87984356/how-old-is-the-grand-canyon |url-status=live }}</ref><ref name="Polyak">{{cite journal |last1=Polyak |first1=Victor |last2=Hill |first2=Carol |last3=Asmerom |first3=Yemane |title=Age and evolution of the Grand Canyon revealed by U-Pb dating of water table-type speleothems |journal=Science |date=March 7, 2008 |volume=319 |issue=5868 |pages=1377–1380 |doi=10.1126/science.1151248 |pmid=18323451 |bibcode=2008Sci...319.1377P |s2cid=206509716 |url=http://doc.rero.ch/record/15735/files/PAL_E3007.pdf |access-date=June 23, 2022 |issn=1095-9203 |archive-date= |archive-url= |url-status= }}</ref>

In another 2008 study, Rebecca Flowers reported on [[apatite]] (U-Th)/He [[Thermochronology|thermochronometry]] results suggesting that parts of the Grand Canyon had reached a depth near to the modern depth around 20{{nbsp}}million years ago.<ref name=NYT-29-Nov-2012/><ref name="Flowers">{{cite journal |last1=Flowers |first1=R.&nbsp;M. |last2=Wernicke |first2=B.&nbsp;P. |last3=Farley |first3=K.&nbsp;A. |title=Unroofing, incision, and uplift history of the southwestern Colorado Plateau from apatite (U-Th)/He thermochronometry |journal=GSA Bulletin |date=May 1, 2008 |volume=120 |issue=5–6 |pages=571–587 |doi=10.1130/B26231.1 |bibcode=2008GSAB..120..571F |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/120/5-6/571/2275/Unroofing-incision-and-uplift-history-of-the |access-date=June 23, 2022 |language=en |issn=0016-7606 |archive-date=June 23, 2022 |archive-url=https://web.archive.org/web/20220623173102/https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/120/5-6/571/2275/Unroofing-incision-and-uplift-history-of-the |url-status=live |url-access=subscription }}</ref>
In a subsequent study published in the journal ''[[Science (journal)|Science]]'' in 2012, she suggested that the western part of the Grand Canyon could be as old as 70{{nbsp}}million years.<ref name="Achenbach">{{cite news |last1=Achenbach |first1=Joel |title=New research revives debate over Grand Canyon's age |url=https://www.washingtonpost.com/national/health-science/new-research-revives-debate-over-grand-canyons-age/2014/01/26/6da35f32-8539-11e3-9dd4-e7278db80d86_story.html |access-date=June 23, 2022 |newspaper=Washington Post |date=January 26, 2014 |archive-date=October 4, 2022 |archive-url=https://web.archive.org/web/20221004020034/https://www.washingtonpost.com/national/health-science/new-research-revives-debate-over-grand-canyons-age/2014/01/26/6da35f32-8539-11e3-9dd4-e7278db80d86_story.html |url-status=live }}</ref><ref name=NYT-29-Nov-2012>{{cite news |last=Wilford |first=John Noble |title=60-Million-Year Debate on Grand Canyon's Age |url=https://www.nytimes.com/2012/11/30/science/earth/study-sees-older-grand-canyon-stirring-controversy.html?_r=0 |access-date=January 22, 2013 |newspaper=New York Times |date=November 29, 2012 |url-status=live |archive-url=https://web.archive.org/web/20130121222602/http://www.nytimes.com/2012/11/30/science/earth/study-sees-older-grand-canyon-stirring-controversy.html?_r=0 |archive-date=January 21, 2013}}</ref><ref>{{Cite journal |last1=Flowers |first1=R.&nbsp;M. |last2=Farley |first2=K.&nbsp;A. |date=December 21, 2012 |title=Apatite 4He/3He and (U-Th)/He Evidence for an Ancient Grand Canyon |journal=Science |language=en |volume=338 |issue=6114 |pages=1616–1619 |doi=10.1126/science.1229390 |issn=0036-8075 |pmid=23196906 |bibcode=2012Sci...338.1616F |s2cid=32277486 |doi-access=free}}</ref><ref>{{cite news |url=http://www.3news.co.nz/Debate-rages-over-Grand-Canyons-origins/tabid/1160/articleID/278924/Default.aspx |work=3 News NZ |title=Grand Canyon as old as the dinosaurs? |date=December 3, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20131031192424/http://www.3news.co.nz/Debate-rages-over-Grand-Canyons-origins/tabid/1160/articleID/278924/Default.aspx |archive-date=October 31, 2013 |access-date=December 2, 2012}}</ref>

The emerging scientific consensus is that the canyon is made up of multiple segments which formed at different times and eventually connected to become the waterway now traversed by the Colorado River. Of the three central segments, the "Hurricane" was formed 50–70{{nbsp}}million years ago, and the "Eastern Grand Canyon" was cut 15–25{{nbsp}}million years ago. In contrast, the "Marble Canyon" and "Westernmost Grand Canyon" segments at the ends of the canyon were carved in the last five to six million years.<ref>{{cite news |last1=Amos |first1=Jonathan |title=Grand Canyon 'formed recently' |url=https://www.bbc.com/news/science-environment-25881953 |access-date=July 11, 2022 |work=BBC News |date=January 26, 2014 |archive-date=July 11, 2022 |archive-url=https://web.archive.org/web/20220711162140/https://www.bbc.com/news/science-environment-25881953 |url-status=live }}</ref><ref>{{cite news |last1=Bush |first1=Mike |title=Debate over the origins of the Grand Canyon - Albuquerque Journal |url=https://www.abqjournal.com/346998/origins-of-the-grand-canyon.html |access-date=July 11, 2022 |work=www.abqjournal.com |date=February 3, 2014 |archive-date=July 11, 2022 |archive-url=https://web.archive.org/web/20220711162140/https://www.abqjournal.com/346998/origins-of-the-grand-canyon.html |url-status=live }}</ref>

The major geologic exposures in the Grand Canyon range in age from the two-billion-year-old [[Vishnu Schist]] at the bottom of the Inner Gorge to the 270-million-year-old [[Kaibab Limestone]] on the Rim. Within that there is a gap, the [[Great Unconformity]], between 1.75{{nbsp}}billion and 1.25{{nbsp}}billion years ago for which no deposits are present.<ref name="Witze"/>

Then, between 1.25{{nbsp}}billion and 730{{nbsp}}million years ago, intermittent sediments began to form the [[Grand Canyon Supergroup]].<ref name="Witze"/> Many of the [[formation (geology)|formations]] were deposited in warm shallow seas, near-shore environments (such as beaches), and swamps as the seashore repeatedly advanced and retreated over the edge of a proto-North America. Major exceptions include the Permian [[Coconino Sandstone]], which contains abundant geological evidence of [[Aeolian processes|aeolian]] sand dune deposition. Several parts of the [[Geology of the Grand Canyon area#Supai Group|Supai Group]] also were deposited in non-marine environments.

The great depth of the Grand Canyon and especially the height of its strata (most of which formed below sea level) can be attributed to {{convert|5000|-|10000|ft|m}} of uplift of the Colorado Plateau, starting about 65{{nbsp}}million years ago (during the [[Laramide orogeny]]). This uplift has steepened the [[stream gradient]] of the Colorado River and its tributaries, which in turn has increased their speed and thus their ability to cut through rock (see the [[Colorado River#Elevation summary|elevation summary]] of the Colorado River for present conditions).

Weather conditions during the [[Quaternary glaciation|ice ages]] also increased the amount of water in the Colorado River drainage system. The ancestral Colorado River responded by cutting its channel faster and deeper.

The base level and course of the Colorado River (or its ancestral equivalent) changed 5.3{{nbsp}}million years ago when the [[Gulf of California]] opened and [[river rejuvenation|lowered the river's base level]] (its lowest point). This increased the rate of erosion and cut nearly all of the Grand Canyon's current depth by 1.2{{nbsp}}million years ago. The [[Fluvial terrace|terraced walls]] of the canyon were created by [[differential erosion]].<ref>{{cite web |url=http://academic.brooklyn.cuny.edu/geology/leveson/core/graphics/nyc_mins2/hyp_test_diff_erode.html |title=The Hypothesis of Differential Erosion |first=David |last=Leveson |access-date=October 22, 2010 |url-status=live |archive-url=https://web.archive.org/web/20110622085241/http://academic.brooklyn.cuny.edu/geology/leveson/core/graphics/nyc_mins2/hyp_test_diff_erode.html |archive-date=June 22, 2011}}</ref>

Between 100,000 and 3{{nbsp}}million years ago, [[Geology of the Grand Canyon area#Volcanic activity in the western canyon|volcanic]] activity deposited ash and lava over the area, which at times completely obstructed the river. These volcanic rocks are the youngest in the canyon.