Editing Precambrian (section)

==Overview==
Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the [[History of the Earth|Earth's history]], and what is known has largely been discovered from the 1960s onwards. The Precambrian fossil record is poorer than that of the succeeding [[Phanerozoic]], and fossils from the Precambrian (e.g. [[stromatolites]]) are of limited [[biostratigraphy|biostratigraphic]] use.<ref name=Monroe>{{cite book |first1=James S. |last1=Monroe |first2=Reed |last2=Wicander |title=The Changing Earth: Exploring Geology and Evolution |edition=2nd |location=Belmont |publisher=[[Wadsworth Publishing Company]] |year=1997 |page=492 |url=https://books.google.com/books?id=48aiAgAAQBAJ&pg=PA492|isbn=9781285981383 }}</ref> This is because many Precambrian rocks have been heavily [[metamorphic rock|metamorphosed]], obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.<ref name=Monroe/><ref>{{cite book |last1=Levin |first1=Harold L. |title=The earth through time |date=2010 |publisher=J. Wiley |location=Hoboken, N.J. |isbn=978-0470387740 |pages=230–233 |edition=9th}} Outlined in {{cite web |first1=Pamela J.W. |last1=Gore |title=The Earliest Earth: 2,100,000,000 years of the Archean Eon |url=http://higheredbcs.wiley.com/legacy/college/levin/0471697435/chap_tut/chaps/chapter08-01.html  |date=25 October 2005}}</ref><ref>{{cite book |chapter=The Precambrian Era |chapter-url=http://geo.msu.edu/extra/geogmich/precambrian.html |publisher=[[Michigan State University]] |last=Davis |first=C.M. |year=1964 |title=Readings in the Geography of Michigan}}</ref>

It is thought that [[formation of the Earth|the Earth coalesced]] from material in orbit around the Sun at roughly 4,543 Ma, and may have been struck by another planet called [[Theia (hypothetical planet)|Theia]] shortly after it formed, splitting off material that formed the [[Moon]] (see [[Giant-impact hypothesis]]). A stable crust was apparently in place by 4,433 Ma, since [[zircon]] crystals from [[Western Australia]] have been [[Radiometric dating|dated]] at 4,404 ± 8 Ma.<ref>{{cite web |url=http://geoscience.wisc.edu/geoscience/people/faculty/john-valley/zircons-are-forever/ |title=Zircons are Forever |access-date=28 April 2007 |year=2005 |work=Department of Geoscience |archive-date=18 May 2019 |archive-url=https://web.archive.org/web/20190518054145/http://geoscience.wisc.edu/geoscience/people/faculty/john-valley/zircons-are-forever/ |url-status=dead }}</ref><ref>{{cite journal |last1=Cavosie |first1=Aaron J. |last2=Valley |first2=John W. |last3=Wilde |first3=Simon A. |title=Chapter 2.5 The Oldest Terrestrial Mineral Record: A Review of 4400 to 4000 Ma Detrital Zircons from Jack Hills, Western Australia |journal=Developments in Precambrian Geology |date=2007 |volume=15 |pages=91–111 |doi=10.1016/S0166-2635(07)15025-8|bibcode=2007DevPG..15...91C |isbn=9780444528100 }}</ref>

{{anchor|supereon}}The term "Precambrian" is used by [[geologist]]s and [[paleontologists]] for general discussions not requiring a more specific eon name. However, both the [[United States Geological Survey]]<ref>{{citation |author=U.S. Geological Survey Geologic Names Committee |title=Divisions of geologic time – major chronostratigraphic and geochronologic units |publisher=[[United States Geological Survey]] |work=U.S. Geological Survey Fact Sheet 2010–3059 |pages=2 |year=2010 |url=https://pubs.usgs.gov/fs/2010/3059/ |access-date=20 June 2018}}</ref> and the [[International Commission on Stratigraphy]] regard the term as informal.<ref>{{cite web |work=[[International Commission on Stratigraphy]] |publisher=[[International Chronostratigraphic Chart]] |date=February 2017 |url=https://stratigraphy.org/chart |first1=Junxuan |last1=Fan |first2=Xudong |last2=Hou |title=Chart |access-date=10 May 2018}}</ref> Because the span of time falling under the Precambrian consists of three eons (the [[Hadean]], the [[Archean]], and the [[Proterozoic]]), it is sometimes described as a ''supereon'',<ref>{{cite journal |last1=Senter |first1=Phil |title=The Age of the Earth & Its Importance to Biology |journal=The American Biology Teacher |date=1 April 2013 |volume=75 |issue=4 |pages=251–256 |doi=10.1525/abt.2013.75.4.5|s2cid=85652369 }}</ref><ref>{{cite journal |last1=Kamp |first1=Ulrich |title=Glaciations |journal=International Encyclopedia of Geography: People, the Earth, Environment and Technology |date=6 March 2017 |pages=1–8 |doi=10.1002/9781118786352.wbieg0612|isbn=9780470659632 }}</ref> but this is also an informal term, not defined by the ICS in its chronostratigraphic guide.<ref>{{cite web |title=Stratigraphic Guide |url=https://stratigraphy.org/guide/chron |website=International Commission on Stratigraphy |at=Table 3 |access-date=9 December 2020}}</ref>

'''''{{vanchor|Eozoic}}''''' (from {{wikt-lang|en|eo-}} "earliest") was a synonym for ''pre-Cambrian'' and ''Precambrian'',<ref>{{cite book|last=Hitchcock|first=C. H.|title=The Geology of New Hampshire|url=https://books.google.com/books?id=zCWO-P0txYYC&pg=PA511|year=1874|page=511|quote= The name ''Eozoic'' seems to have been proposed by Dr. [[J.W. Dawson]], of Montreal, in 1865. He did not fully define the limits of its application at that time; but it seems to have been generally understood by geologists to embrace all the obscurely fossiliferous rocks older than the Cambrian.}}</ref><ref>{{cite book|title=Bulletin|url=https://books.google.com/books?id=YngeAQAAIAAJ&pg=RA3-PA28|volume=767|year=1925|publisher=U.S. Government Printing Office|page=3|quote= [1888] Sir [[J. W. Dawson]] prefers the term "Eozoic" [to Archean], and would have it include all the Pre-Cambrian strata.}}</ref> or more specifically ''[[Archean]]''.<ref>{{cite book|last=Salop|first=L.J.|title=Geological Evolution of the Earth During the Precambrian|url=https://books.google.com/books?id=SmX7CAAAQBAJ&pg=PA9|year=2012|publisher=Springer|isbn=978-3-642-68684-9|page=9|quote=  a possibility of dividing the Precambrian history into two eons: the Eozoic, embracing the Archean Era only, and the Protozoic, comprising all the remaining Precambrian Eras.}}</ref>