View source for Precambrian

{{Short description|History of Earth 4600–539 million years ago}}
{{For|the album by German band The Ocean|Precambrian (album){{!}}''Precambrian'' (album)}}
{{Redirect|Cryptozoic|the games publisher|Cryptozoic Entertainment}}
{{Infobox geologic timespan
| name                      = Precambrian
| color                     = Precambrian
| top_bar                   = all time
| time_start                = {{period start|precambrian}}
| time_start_uncertainty    = {{period start error|precambrian|sign=no}}
| time_end                  = {{period end|precambrian}}
| time_end_uncertainty      = {{period end error|precambrian|sign=no}}
<!--Chronology-->
| timeline                  = Eons
| proposed_subdivision1     = See [[Geologic time scale#Proposed Precambrian timeline|Proposed Precambrian timeline]]
<!--Etymology-->
| synonym1                  = Cryptozoic
| synonym1_coined           =
<!--Usage Information-->
| celestial_body            = earth
| usage                     = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used           = ICS Time Scale
<!--Definition-->
| chrono_unit               = supereon
| strat_unit                = supereonothem
| proposed_by               =
| timespan_formality        = Informal
| lower_boundary_def        = Formation of the [[Earth]]
| lower_gssa_accept_date    = {{period start ratification|precambrian}}
| upper_boundary_def        = Appearance of the [[Trace fossil|Ichnofossil]] ''[[Treptichnus pedum]]''
| upper_gssp_location       = [[Fortune Head|Fortune Head section]], Newfoundland, Canada
| upper_gssp_coords         = {{Coord|47.0762|N|55.8310|W|display=inline}}
| upper_gssp_accept_date    = {{period end ratification|precambrian}}
}}
The '''Precambrian''' ({{IPAc-en|pron|p|r|i|ˈ|k|æ|m|b|r|i|.|ə|n|,_|-|ˈ|k|eɪ|m|-}} {{respell|pree|KAM|bree|ən|,_|-KAYM|-}};{{refn|{{Cite Collins Dictionary|Precambrian|access-date=2023-08-30}}}} '''pre-Cambrian''', or '''Cryptozoic''', sometimes abbreviated '''pꞒ''' or '''PreꞒ''') is the earliest part of [[History of the Earth|Earth's history]], set before the current [[Phanerozoic]] Eon. The Precambrian is so named because it preceded the [[Cambrian]], the first [[geologic period|period]] of the Phanerozoic Eon, which is named after [[Cambria]], the Latinized name for [[Wales]], where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time.

The Precambrian is an informal unit of geologic time,<ref>{{cite book |last1=Van Kranendonk |first1=Martin J. |last2=Altermann |first2=Wladyslaw |last3=Beard |first3=Brian L. |last4=Hoffman |first4=Paul F. |last5=Johnson |first5=Clark M. |last6=Kasting |first6=James F. |last7=Melezhik |first7=Victor A. |last8=Nutman |first8=Allen P. |last9=Papineau |first9=Dominic |last10=Pirajno |first10=Franco |title=The Geologic Time Scale |chapter=A Chronostratigraphic Division of the Precambrian |date=2012 |pages=299–392 |doi=10.1016/B978-0-444-59425-9.00016-0 |isbn=978-0-444-59425-9 }}</ref> subdivided into three [[eon (geology)|eons]] ([[Hadean]], [[Archean]], [[Proterozoic]]) of the [[geologic time scale]]. It spans from the formation of Earth about 4.6 billion years ago ([[Ga (unit)|Ga]]) to the beginning of the Cambrian Period, about {{Period end|Precambrian}} million years ago ([[Ma (unit)|Ma]]), when hard-shelled creatures first appeared in abundance.

==Overview==
Relatively little is known about the Precambrian, despite it making up roughly eight-ninths 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=978-1-285-98138-3 }}</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=978-0-470-38774-0 |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/ }}</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=978-0-444-52810-0 }}</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 |page=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 icc}} 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=April 2013 |volume=75 |issue=4 |pages=251–256 |doi=10.1525/abt.2013.75.4.5 }}</ref><ref>{{cite book |last1=Kamp |first1=Ulrich  |title=International Encyclopedia of Geography |chapter=Glaciations |date=6 March 2017 |pages=1–8 |doi=10.1002/9781118786352.wbieg0612|isbn=978-0-470-65963-2 }}</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>

The oldest fossils found in what was previously called [[Azoic Age|Azoic]] rock, established the geological boundary between the Precambrian and [[Cambrian]].<ref name=":0">{{Cite book |last=Toghill|first=Peter|title=The Geology of Britain: An Introduction|publisher=Swan Hill Press|year=2000|isbn=9781853108907|pages=33}}</ref><ref>{{Cite web |title=GEOL 102 Introduction to the Strange Aeons of the Precambrian: The Hadean Eon|url=https://www.geol.umd.edu/~tholtz/G102/lectures/102hadean.html|access-date=2026-03-20|website=www.geol.umd.edu}}</ref>

'''''{{vanchor|Eozoic}}''''' (from {{wikt-lang|en|eo-}} "earliest") was a synonym for ''pre-Cambrian'' or ''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>

==Life forms==
{{Further|Origin of life|Avalon explosion|Earliest known life forms}}
A specific date for the origin of life has not been determined. [[Carbon]] found in 3.8 billion-year-old rocks (Archean Eon) from islands off western [[Greenland]] may be of organic origin. Well-preserved microscopic fossils of [[bacteria]] older than 3.46 billion years have been found in [[Western Australia]].<ref>{{cite book |last1=Brun |first1=Yves |author-link=Yves Brun |first2=Lawrence J. |last2=Shimkets |title=Prokaryotic development |publisher=[[ASM Press]] |date=January 2000 |page=114 |isbn=978-1-55581-158-7 |url=https://books.google.com/books?id=wRxrAAAAMAAJ}}</ref> Probable fossils 100 million years older have been found in the same area. However, there is evidence that life could have evolved over 4.280 billion years ago.<ref name="NAT-20170301">{{cite journal |author=Dodd, Matthew S. |author2=Papineau, Dominic |author3=Grenne, Tor |author4=slack, John F. |author5=Rittner, Martin |author6=Pirajno, Franco |author7=O'Neil, Jonathan |author8=Little, Crispin T. S. |title=Evidence for early life in Earth's oldest hydrothermal vent precipitates|journal=Nature |volume=543 |issue=7643 |pages=60–64 |date=2 March 2017 | doi=10.1038/nature21377|pmid=28252057 |bibcode=2017Natur.543...60D |doi-access=free }}</ref><ref name="NYT-20170301">{{cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |title=Scientists Say Canadian Bacteria Fossils May Be Earth's Oldest |url=https://www.nytimes.com/2017/03/01/science/earths-oldest-bacteria-fossils.html |date=1 March 2017 |work=[[The New York Times]] |access-date=2 March 2017 }}</ref><ref name="BBC-20170301">{{cite web |last=Ghosh |first=Pallab |title=Earliest evidence of life on Earth 'found' |url=https://www.bbc.co.uk/news/science-environment-39117523 |work=[[BBC News]] |date=1 March 2017 |access-date=2 March 2017}}</ref><ref name="4.3b oldest">{{cite news |last1=Dunham |first1=Will |title=Canadian bacteria-like fossils called oldest evidence of life |url=http://ca.reuters.com/article/topNews/idCAKBN16858B?sp=true |archive-url=https://web.archive.org/web/20170302114728/http://ca.reuters.com/article/topNews/idCAKBN16858B?sp=true |archive-date=March 2, 2017 |date=1 March 2017 |work=[[Reuters]] |access-date=1 March 2017 }}</ref> There is a fairly solid record of bacterial life throughout the remainder (Proterozoic Eon) of the Precambrian.

Complex multicellular organisms may have appeared as early as 2100 Ma.<ref>{{cite journal |last1=Albani |first1=Abderrazak El |last2=Bengtson |first2=Stefan |last3=Canfield |first3=Donald E. |last4=Bekker |first4=Andrey |last5=Macchiarelli |first5=Roberto |last6=Mazurier |first6=Arnaud |last7=Hammarlund |first7=Emma U. |last8=Boulvais |first8=Philippe |last9=Dupuy |first9=Jean-Jacques |last10=Fontaine |first10=Claude |last11=Fürsich |first11=Franz T. |last12=Gauthier-Lafaye |first12=François |last13=Janvier |first13=Philippe |last14=Javaux |first14=Emmanuelle |last15=Ossa |first15=Frantz Ossa |last16=Pierson-Wickmann |first16=Anne-Catherine |last17=Riboulleau |first17=Armelle |last18=Sardini |first18=Paul |last19=Vachard |first19=Daniel |last20=Whitehouse |first20=Martin |last21=Meunier |first21=Alain |title=Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago |journal=Nature |date=July 2010 |volume=466 |issue=7302 |pages=100–104 |doi=10.1038/nature09166|pmid=20596019 |bibcode=2010Natur.466..100A }}</ref> However, the interpretation of ancient fossils is problematic, and "... some definitions of multicellularity encompass everything from simple bacterial colonies to badgers."<ref>{{cite journal |last1=Donoghue |first1=Philip C. J. |last2=Antcliffe |first2=Jonathan B. |title=Origins of multicellularity |journal=Nature |date=July 2010 |volume=466 |issue=7302 |pages=41–42 |doi=10.1038/466041a |pmid=20596008 }}</ref> Other possible early complex multicellular organisms include a possible 2450 Ma red alga from the [[Kola Peninsula]],<ref>{{cite journal |last1=Rozanov |first1=A. Yu. |last2=Astafieva |first2=M. M. |title=A unique find of the earliest multicellular algae in the Lower Proterozoic (2.45 Ga) of the Kola Peninsula |journal=Doklady Biological Sciences |date=March 2013 |volume=449 |issue=1 |pages=96–98 |doi=10.1134/S0012496613020051 |pmid=23652437 }}</ref> 1650 Ma carbonaceous biosignatures in north China,<ref>{{cite journal |last1=Qu |first1=Yuangao |last2=Zhu |first2=Shixing |last3=Whitehouse |first3=Martin |last4=Engdahl |first4=Anders |last5=McLoughlin |first5=Nicola |title=Carbonaceous biosignatures of the earliest putative macroscopic multicellular eukaryotes from 1630 Ma Tuanshanzi Formation, north China |journal=Precambrian Research |date=January 2018 |volume=304 |pages=99–109 |doi=10.1016/j.precamres.2017.11.004|bibcode=2018PreR..304...99Q }}</ref> the 1600 Ma ''[[Rafatazmia]]'',<ref>{{cite journal |last1=Bengtson |first1=Stefan |last2=Sallstedt |first2=Therese |last3=Belivanova |first3=Veneta |last4=Whitehouse |first4=Martin |title=Three-dimensional preservation of cellular and subcellular structures suggests 1.6 billion-year-old crown-group red algae |journal=PLOS Biology |date=14 March 2017 |volume=15 |issue=3 |article-number=e2000735 |doi=10.1371/journal.pbio.2000735|pmid=28291791 |pmc=5349422 |doi-access=free }}</ref> and a possible 1047 Ma ''[[Bangiomorpha]]'' red alga from the Canadian Arctic.<ref>{{cite journal |last1=Gibson |first1=Timothy M. |last2=Shih |first2=Patrick M. |last3=Cumming |first3=Vivien M. |last4=Fischer |first4=Woodward W. |last5=Crockford |first5=Peter W. |last6=Hodgskiss |first6=Malcolm S.W. |last7=Wörndle |first7=Sarah |last8=Creaser |first8=Robert A. |last9=Rainbird |first9=Robert H. |last10=Skulski |first10=Thomas M. |last11=Halverson |first11=Galen P. |title=Precise age of Bangiomorpha pubescens dates the origin of eukaryotic photosynthesis |journal=Geology |date=February 2018 |volume=46 |issue=2 |pages=135–138 |doi=10.1130/G39829.1 |bibcode=2018Geo....46..135G }}</ref> The earliest fossils widely accepted as complex multicellular organisms date from the Ediacaran Period.<ref>{{cite journal |last1=Laflamme |first1=M. |title=Modeling morphological diversity in the oldest large multicellular organisms |journal=Proceedings of the National Academy of Sciences |date=9 September 2014 |volume=111 |issue=36 |pages=12962–12963 |doi=10.1073/pnas.1412523111|pmid=25114212 |pmc=4246935 |bibcode=2014PNAS..11112962L |doi-access=free }}</ref><ref>{{cite journal |last1=Kolesnikov |first1=Anton V. |last2=Rogov |first2=Vladimir I. |last3=Bykova |first3=Natalia V. |last4=Danelian |first4=Taniel |last5=Clausen |first5=Sébastien |last6=Maslov |first6=Andrey V. |last7=Grazhdankin |first7=Dmitriy V. |title=The oldest skeletal macroscopic organism Palaeopascichnus linearis |journal=Precambrian Research |date=October 2018 |volume=316 |pages=24–37 |doi=10.1016/j.precamres.2018.07.017 |bibcode=2018PreR..316...24K }}</ref> A very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as [[Ediacaran biota|Ediacaran or Vendian biota]]. Hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic Eon. By the middle of the following Cambrian Period, a very diverse fauna is recorded in the [[Burgess Shale]], including some which may represent stem groups of modern taxa. The increase in diversity of lifeforms during the early Cambrian is called the [[Cambrian explosion]] of life.<ref>{{cite book|last1=Fedonkin|first1=Mikhail A.|author-link=Mikhail A. Fedonkin|last2=Gehling|first2=James G.|last3=Grey|first3=Kathleen|last4=Narbonne|first4=Guy M.|last5=Vickers-Rich|first5=Patricia|author5-link=Patricia Vickers-Rich|others=Foreword by [[Arthur C. Clarke]]|date=2007|title=The Rise of Animals: Evolution and Diversification of the Kingdom Animalia|location=Baltimore, Maryland|publisher=[[Johns Hopkins University Press]]|isbn=978-0-8018-8679-9|lccn=2007061351|oclc=85162342|ol=17256629M}}</ref><ref>{{cite book |last1=Dawkins |first1=Richard |author-link=Richard Dawkins |title=The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution |year=2005 |publisher=[[Houghton Mifflin Harcourt]] |isbn=978-0-618-61916-0 |first2=Yan |last2=Wong  |url=https://archive.org/details/ancestorstale00rich_0 |url-access=registration |pages=[https://archive.org/details/ancestorstale00rich_0/page/n696 673]}}</ref>

While land seems to have been devoid of plants and animals, cyanobacteria and other microbes formed prokaryotic [[Algal mat|mats]] that covered terrestrial areas.<ref>{{Cite encyclopedia |url=http://www.paulselden.net/uploads/7/5/3/2/7532217/elsterrestrialization.pdf |title=Terrestrialization (Precambrian–Devonian) |last=Selden |first=Paul A. |year=2005 |encyclopedia=[[Encyclopedia of Life Sciences]] |publisher=[[John Wiley & Sons, Ltd.]] |doi=10.1038/npg.els.0004145 |isbn=978-0-470-01617-6 }}</ref>

Tracks from an animal with leg-like appendages have been found in what was mud 551 million years ago.<ref>{{cite news |last1=Sharman |first1=Jon |last2=Barnes |first2=Tom |title=Scientists discover 'oldest footprints on Earth' in southern China dating back 500 million years |url=https://www.independent.co.uk/news/science/archaeology/oldest-fossil-footprints-china-found-discovered-yangtze-virginia-tech-a8386911.html |work=The Independent |date=7 June 2018 }}</ref><ref>{{cite journal |last1=Chen |first1=Zhe |last2=Chen |first2=Xiang |last3=Zhou |first3=Chuanming |last4=Yuan |first4=Xunlai |last5=Xiao |first5=Shuhai |title=Late Ediacaran trackways produced by bilaterian animals with paired appendages |journal=Science Advances |date=June 2018 |volume=4 |issue=6 |article-number=eaao6691 |doi=10.1126/sciadv.aao6691|pmid=29881773 |pmc=5990303 |bibcode=2018SciA....4.6691C }}</ref>

===Emergence of life===

The [[RNA world]] hypothesis asserts that RNA evolved before coded proteins and DNA genomes.<ref>{{cite journal |vauthors=Fine JL, Pearlman RE |title=On the origin of life: an RNA-focused synthesis and narrative |journal=RNA |volume=29 |issue=8 |pages=1085–98 |date=August 2023 |pmid=37142437 |pmc=10351881 |doi=10.1261/rna.079598.123 }}</ref> During the Hadean Eon (4,567–4,031 Ma) abundant [[Geothermal activity|geothermal]] [[Microenvironment (ecology)|microenvironment]]s were present that may have had the potential to support the synthesis and replication of [[RNA]] and thus possibly the evolution of a primitive life form. It was shown that porous rock systems comprising heated air-water interfaces could allow [[ribozyme]]-[[Catalysis|catalyzed]] RNA replication of sense and antisense strands that could be followed by strand-dissociation, thus enabling combined synthesis, release and folding of active ribozymes.<ref name="Salditt2023">{{cite journal |vauthors=Salditt A, Karr L, Salibi E, Le Vay K, Braun D, Mutschler H |date=March 2023 |title=Ribozyme-mediated RNA synthesis and replication in a model Hadean microenvironment |journal=Nat Commun |volume=14 |issue=1 |bibcode=2023NatCo..14.1495S |doi=10.1038/s41467-023-37206-4 |pmc=10023712 |pmid=36932102 |article-number=1495}}</ref> This primitive RNA replicative system also may have been able to undergo template strand switching during replication ([[genetic recombination]]) as is known to occur during the RNA replication of extant [[coronavirus]]es.<ref>{{cite journal |vauthors=Su S, Wong G, Shi W, Liu J, Lai AC, Zhou J, Liu W, Bi Y, Gao GF |title=Epidemiology, Genetic Recombination, and Pathogenesis of Coronaviruses |journal=Trends Microbiol |volume=24 |issue=6 |pages=490–502 |date=June 2016 |pmid=27012512 |pmc=7125511 |doi=10.1016/j.tim.2016.03.003 }}</ref>

==Planetary environment and the oxygen catastrophe==

[[File:Temagami greenstone belt pillow lava.jpg|thumb|Weathered Precambrian [[pillow lava]] in the [[Temagami Greenstone Belt]] of the [[Canadian Shield]]]]
Evidence of the details of [[plate tectonics|plate motions]] and other [[tectonic]] activity in the Precambrian is difficult to interpret. It is generally believed that small proto-continents existed before 4280 Ma, and that most of the Earth's landmasses collected into a single [[supercontinent]] around 1130 Ma. The supercontinent, known as [[Rodinia]], broke up around 750 Ma. A number of [[glaciation|glacial periods]] have been identified going as far back as the [[Huronian]] epoch, roughly 2400–2100 Ma. One of the best studied is the [[Sturtian-Varangian]] glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a "[[Snowball Earth]]".<ref>{{Cite journal |last1=Hoffman |first1=Paul F. |last2=Abbot |first2=Dorian S. |last3=Ashkenazy |first3=Yosef |last4=Benn |first4=Douglas I. |last5=Brocks |first5=Jochen J. |last6=Cohen |first6=Phoebe A. |last7=Cox |first7=Grant M. |last8=Creveling |first8=Jessica R. |last9=Donnadieu |first9=Yannick |last10=Erwin |first10=Douglas H. |last11=Fairchild |first11=Ian J. |last12=Ferreira |first12=David |last13=Goodman |first13=Jason C. |last14=Halverson |first14=Galen P. |last15=Jansen |first15=Malte F. |display-authors=8 |date=2017-11-08 |title=Snowball Earth climate dynamics and Cryogenian geology-geobiology |journal=Science Advances |volume=3 |issue=11 |article-number=e1600983 |doi=10.1126/sciadv.1600983 |pmc=5677351 |pmid=29134193|bibcode=2017SciA....3E0983H }}</ref><ref>{{cite journal |last1=Parnell |first1=John |title=Snowball Earth to Global Warming: Coupled vanadium-carbonaceous deposits in the Cryogenian-Cambrian |journal=Ore Geology Reviews |date=June 2022 |volume=145 |article-number=104876 |doi=10.1016/j.oregeorev.2022.104876 |bibcode=2022OGRv..14504876P |hdl=2164/18433 |hdl-access=free }}</ref>

It is believed that [[molecular]] oxygen was not a significant fraction of Earth's atmosphere until after [[photosynthesis|photosynthetic]] life forms evolved and began to produce it in large quantities as a byproduct of their [[metabolism]]. This radical shift from a chemically inert to an oxidizing atmosphere caused an [[ecological crisis]], sometimes called the [[Great Oxygenation Event|oxygen catastrophe]]. At first, [[oxygen]] would have quickly combined with other elements in Earth's crust, primarily iron, removing it from the atmosphere. After the supply of oxidizable surfaces ran out, oxygen would have begun to accumulate in the atmosphere, and the modern high-oxygen atmosphere would have developed. Evidence for this lies in older rocks that contain massive [[banded iron formation]]s that were laid down as iron oxides.<ref>{{Citation |last1=Kump |first1=Lee R. |title=8.1 The Great Oxidation Event |date=2013 |work=Reading the Archive of Earth's Oxygenation: Volume 3: Global Events and the Fennoscandian Arctic Russia - Drilling Early Earth Project |pages=1517–1533 |editor-last=Melezhik |editor-first=Victor A. |place=Berlin, Heidelberg |publisher=Springer |language=en |doi=10.1007/978-3-642-29670-3_11 |isbn=978-3-642-29670-3 |last2=Fallick |first2=Anthony E. |last3=Melezhik |first3=Victor A. |last4=Strauss |first4=Harald |last5=Lepland |first5=Aivo |editor2-last=Prave |editor2-first=Anthony R. |editor3-last=Hanski |editor3-first=Eero J. |editor4-last=Fallick |editor4-first=Anthony E. }}</ref><ref>{{Cite journal |last1=Konhauser |first1=Kurt O. |last2=Pecoits |first2=Ernesto |last3=Lalonde |first3=Stefan V. |last4=Papineau |first4=Dominic |last5=Nisbet |first5=Euan G. |last6=Barley |first6=Mark E. |last7=Arndt |first7=Nicholas T. |last8=Zahnle |first8=Kevin |last9=Kamber |first9=Balz S. |date=2009 |title=Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event |journal=Nature |volume=458 |issue=7239 |pages=750–753 |doi=10.1038/nature07858 |pmid=19360085 |bibcode=2009Natur.458..750K }}</ref>

==Subdivisions==
{{main|Timetable of the Precambrian}}

{{Life timeline}}
A terminology has evolved covering the early years of the Earth's existence, as [[radiometric dating]] has allowed absolute dates to be assigned to specific formations and features.<ref>{{cite web| url = https://www.geosociety.org/science/timescale/| title = Geological Society of America's "2009 GSA Geologic Time Scale."| access-date = 2019-08-29| archive-date = 2020-11-05| archive-url = https://web.archive.org/web/20201105231837/https://www.geosociety.org/science/timescale/}}</ref> The Precambrian is divided into three eons: the [[Hadean]] ({{Period start|Hadean}}–{{Period start|Archean}} Ma), [[Archean]] ({{Period start|Archean}}-{{Period start|Proterozoic}} Ma) and [[Proterozoic]] ({{Period start|Proterozoic}}-{{Period start|Cambrian}} Ma). See [[Timetable of the Precambrian]].
* [[Proterozoic]]: this eon refers to the time from the lower [[Cambrian]] boundary, {{Period start|Cambrian}} Ma, back through {{Period start|Proterozoic}} Ma. As originally used, it was a synonym for "Precambrian" and hence included everything prior to the Cambrian boundary.<ref>{{cite journal |last1=Plumb |first1=Kenneth A. |last2=James |first2=Harold L. |title=Subdivision of precambrian time: recommendations and suggestions by the subcommission on precambrian stratigraphy |journal=Precambrian Research |date=July 1986 |volume=32 |issue=1 |pages=65–92 |doi=10.1016/0301-9268(86)90031-8 |bibcode=1986PreR...32...65P }}</ref> The Proterozoic Eon is divided into three eras: the [[Neoproterozoic]], [[Mesoproterozoic]] and [[Paleoproterozoic]].
** [[Neoproterozoic]]: The youngest [[geologic era]] of the Proterozoic Eon, from the [[Cambrian]] Period lower boundary ({{Period start|Cambrian}} Ma) back to {{Period start|Neoproterozoic}} Ma. The Neoproterozoic corresponds to Precambrian Z rocks of older North American stratigraphy.
*** [[Ediacaran]]: The youngest [[geologic period]] within the Neoproterozoic Era. The "2012 Geologic Time Scale" dates it from {{Period start|Cambrian}} to {{Period start|Ediacaran}} Ma. In this period the [[Ediacaran biota]] appeared.
*** [[Cryogenian]]: The middle period in the [[Neoproterozoic]] Era: {{Period start|Ediacaran}}-{{Period start|Cryogenian}} Ma.
*** [[Tonian]]: the earliest period of the Neoproterozoic Era: {{Period start|Cryogenian}}-{{Period start|Tonian}} Ma.
** [[Mesoproterozoic]]: the middle era of the [[Proterozoic]] Eon, {{Period start|Neoproterozoic}}-{{Period start|Mesoproterozoic}} Ma. Corresponds to "Precambrian Y" rocks of older North American stratigraphy.
** [[Paleoproterozoic]]: oldest era of the Proterozoic Eon, {{Period start|Mesoproterozoic}}-{{Period start|Paleoproterozoic}} Ma. Corresponds to "Precambrian X" rocks of older North American stratigraphy.
* [[Archean]] Eon: {{Period start|Proterozoic}}-{{Period start|Archean}} Ma.
* [[Hadean]] Eon: {{Period start|Archean}}–{{Period start|Hadean}} Ma. This term was intended originally to cover the time before any preserved rocks were deposited, although some [[zircon]] crystals from about 4400 Ma demonstrate the existence of crust in the Hadean Eon. Other records from Hadean time come from the [[Geology of the Moon|Moon]] and [[meteorite]]s.<ref>{{cite journal |last1=Harrison |first1=T. Mark |title=The Hadean Crust: Evidence from >4 Ga Zircons |journal=Annual Review of Earth and Planetary Sciences |date=27 April 2009 |volume=37 |issue=1 |pages=479–505 |doi=10.1146/annurev.earth.031208.100151 |bibcode=2009AREPS..37..479H }}</ref><ref>{{cite journal |last1=Abramov |first1=Oleg |last2=Kring |first2=David A. |last3=Mojzsis |first3=Stephen J. |title=The impact environment of the Hadean Earth |journal=Geochemistry |date=October 2013 |volume=73 |issue=3 |pages=227–248 |doi=10.1016/j.chemer.2013.08.004 |bibcode=2013ChEG...73..227A }}</ref>
It has been proposed that the Precambrian should be divided into eons and eras that reflect stages of planetary evolution, rather than the current scheme based upon numerical ages. Such a system could rely on events in the stratigraphic record and be demarcated by [[Global Boundary Stratotype Section and Point|GSSPs]]. The Precambrian could be divided into five "natural" eons, characterized as follows:<ref>{{cite book |last1=Bleeker |first1=W. |title=A Geologic Time Scale 2004 |chapter=Toward a 'natural' Precambrian time scale |date=2005 |pages=141–146 |doi=10.1017/CBO9780511536045.011 |isbn=978-0-521-78673-7 |editor-first1=Felix M. |editor-first2=James G. |editor-first3=Alan G. |editor-last1=Gradstein |editor-last2=Ogg |editor-last3=Smith |editor1-link=Felix M. Gradstein |editor3-link=Alan Gilbert Smith }}</ref>
# Accretion and differentiation: a period of planetary formation until [[Giant impact hypothesis|giant Moon-forming impact event]].
# Hadean: dominated by heavy bombardment from about 4.51 Ga (possibly including a [[cool early Earth]] period) to the end of the [[Late Heavy Bombardment]] period.
# Archean: a period defined by the first crustal formations (the [[Isua greenstone belt]]) until the deposition of [[banded iron formation]]s due to increasing atmospheric oxygen content.
# Transition: a period of continued banded iron formation until the first continental [[red beds]].
# Proterozoic: a period of modern [[plate tectonics]] until the first [[animal]]s.

==Precambrian supercontinents==
The movement of Earth's [[Plate tectonics|plates]] has caused the formation and break-up of continents over time, including occasional formation of a [[supercontinent]] containing most or all of the landmass. The earliest known supercontinent was [[Vaalbara]]. It formed from proto-continents and was a supercontinent 3.636 billion years ago. Vaalbara broke up c. 2.845–2.803 [[Giga-annum|Ga]] ago. The supercontinent [[Kenorland]] was formed c. 2.72 Ga ago and then broke sometime after 2.45–2.1 Ga into the proto-continent [[craton]]s called [[Laurentia]], [[Baltica]], [[Yilgarn craton]] and [[Kalahari craton|Kalahari]]. The supercontinent [[Columbia (supercontinent)|Columbia]], or Nuna, formed 2.1–1.8 billion years ago and broke up about 1.3–1.2 billion years ago.<ref name="Zhao1">{{Cite journal |first=Guochun |last=Zhao |author2 = Cawood, Peter A. |author3 = Wilde, Simon A. |author4 = Sun, M. |date=2002|title=Review of global 2.1–1.8 Ga orogens: implications for a pre-Rodinia super-continent |journal=Earth-Science Reviews |volume=59 |issue=1 |pages=125–162 |doi=10.1016/S0012-8252(02)00073-9 |bibcode=2002ESRv...59..125Z}}</ref><ref name="Zhao2">{{cite journal |last1=Zhao |first1=Guochun |last2=Sun |first2=Min |last3=Wilde |first3=Simon A. |last4=Li |first4=Sanzhong |title=A Paleo-Mesoproterozoic supercontinent: assembly, growth and breakup |journal=Earth-Science Reviews |date=September 2004 |volume=67 |issue=1–2 |pages=91–123 |doi=10.1016/j.earscirev.2004.02.003 |bibcode=2004ESRv...67...91Z }}</ref> The supercontinent [[Rodinia]] is thought to have formed about 1300-900 Ma, to have included most or all of Earth's continents and to have broken up into eight continents around 750–600 million years ago.<ref>{{cite journal |last1=Li |first1=Z.X. |last2=Bogdanova |first2=S.V. |last3=Collins |first3=A.S. |last4=Davidson |first4=A. |last5=De Waele |first5=B. |last6=Ernst |first6=R.E. |last7=Fitzsimons |first7=I.C.W. |last8=Fuck |first8=R.A. |last9=Gladkochub |first9=D.P. |last10=Jacobs |first10=J. |last11=Karlstrom |first11=K.E. |last12=Lu |first12=S. |last13=Natapov |first13=L.M. |last14=Pease |first14=V. |last15=Pisarevsky |first15=S.A. |last16=Thrane |first16=K. |last17=Vernikovsky |first17=V. |title=Assembly, configuration, and break-up history of Rodinia: A synthesis |journal=Precambrian Research |date=January 2008 |volume=160 |issue=1–2 |pages=179–210 |doi=10.1016/j.precamres.2007.04.021 |bibcode=2008PreR..160..179L }}</ref>

<gallery>
File:Kenorland.jpg|Map of [[Kenorland]] supercontinent 2.5 billion years ago{{citation needed|date=April 2024}}
File:Kenorland breaking up.jpg|Map of Kenorland breaking up 2.3 billion years ago{{citation needed|date=April 2024}}
File:Paleoglobe NO 1590 mya-vector-colors.svg|The supercontinent [[Columbia (supercontinent)|Columbia]] about 1.6 billion years ago
File:Positions of ancient continents, 550 million years ago.jpg|Landmass positions near the end of the Precambrian{{citation needed|date=April 2024}}
</gallery>

==See also==
* {{annotated link|Phanerozoic}}
** {{annotated link|Paleozoic}}
** {{annotated link|Mesozoic}}
** {{annotated link|Cenozoic}}
* {{annotated link|Precambrian Research}}

==References==
<references />

==Further reading==
* Valley, John W., William H. Peck, Elizabeth M. King (1999) ''Zircons Are Forever'', The Outcrop for 1999, University of Wisconsin-Madison [http://www.geology.wisc.edu/~valley/zircons/zircon_home.html Wgeology.wisc.edu] {{Webarchive|url=https://web.archive.org/web/20120316170539/http://www.geology.wisc.edu/~valley/zircons/zircon_home.html |date=2012-03-16 }} – ''Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago'' Accessed Jan. 10, 2006
* {{cite journal |last1=Wilde |first1=Simon A. |last2=Valley |first2=John W. |last3=Peck |first3=William H. |last4=Graham |first4=Colin M. |title=Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago |journal=Nature |date=January 2001 |volume=409 |issue=6817 |pages=175–178 |doi=10.1038/35051550 |pmid=11196637 |bibcode=2001Natur.409..175W }}
* {{cite journal |last=Wyche |first=S. |author2=Nelson, D. R. |author3=Riganti, A.  |date=2004 |title=4350–3130 Ma detrital zircons in the Southern Cross Granite–Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn Craton |journal=Australian Journal of Earth Sciences |volume=51 |issue=1 |pages=31–45 |doi=10.1046/j.1400-0952.2003.01042.x |bibcode=2004AuJES..51...31W}}

==External links==
{{Commons category|Precambrian}}
* [http://www.scotese.com/precambr.htm Late Precambrian Supercontinent and Ice House World] from the Paleomap Project

{{Clear}}
{{Geological history|c}}

{{Authority control}}

[[Category:Precambrian| ]]