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{{short description|Third eon of the geologic timescale, last eon of the Precambrian Supereon}}
{{Infobox geologic timespan
| name = Proterozoic
| color = Proterozoic
| top_bar = all time
| time_start = 2500
| time_end = 538.8
| time_end_prefix =
| time_end_uncertainty = 0.2
| image_map =
| caption_map =
| image_outcrop =
| caption_outcrop =
| image_art = Proterozoic collage.png
| caption_art = From left to right: Four main Proterozoic events: [[Great Oxidation Event]] and subsequent [[Huronian glaciation]]; First [[eukaryotes]], like [[red algae]]; [[Snowball Earth]] in [[Cryogenian]] period; [[Ediacaran biota]]<ref>[https://www.flickr.com/photos/ideonexus/albums/72157603838941938 Smithsonian National Museum] ''flickr''.</ref>

| timeline = Eons
| former_subdivisions =
| formerly_part_of =
| partially_contained_in =
| partially_contains =

| chrono_name =
| strat_name =
| name_formality = Formal
| name_accept_date =
| alternate_spellings =
| synonym1 =
| synonym1_coined =
| synonym2 =
| synonym2_coined =
| synonym3 =
| synonym3_coined =
| former_names =
| proposed_names =

| celestial_body = earth
| usage = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used = ICS Time Scale
| formerly_used_by =
| not_used_by =

| chrono_unit = Eon
| strat_unit = Eonothem
| proposed_by =
| timespan_formality = Formal
| lower_boundary_def = Defined Chronometrically
| lower_gssa_accept_date = 1991<ref>{{cite journal |last1=Plumb |first1=K. A. |title=New Precambrian time scale |journal=Episodes |date=June 1, 1991 |volume=14 |issue=2 |pages=139–140 |doi=10.18814/epiiugs/1991/v14i2/005 |url=https://www.episodes.org/journal/view.html?doi=10.18814/epiiugs/1991/v14i2/005 |access-date=16 January 2023|doi-access=free }}</ref>
| 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 = 1992
}}
The '''Proterozoic''' ({{IPAc-en|ipa|ˌ|p|r|oʊ|t|ər|ə|ˈ|z|oʊ|ɪ|k|,_|p|r|ɒ|t|-|,_|-|ər|oʊ|-|,_|-|t|r|ə|-|,_|-|t|r|oʊ|-}}){{refn|{{cite web |url=https://www.oxforddictionaries.com/definition/english/Proterozoic |archive-url=https://web.archive.org/web/20120724122625/http://oxforddictionaries.com/definition/english/Proterozoic |url-status=dead |archive-date=July 24, 2012 |title=Proterozoic – definition of Proterozoic in English from the Oxford dictionary |publisher=[[OxfordDictionaries.com]] |access-date=2016-01-20 }} }}{{refn|{{MerriamWebsterDictionary|Proterozoic}}}}<ref>{{dictionary.com|Proterozoic}}</ref> is the third of the four [[eon (geology)|geologic eon]]s of [[Earth's history]], spanning the time interval from 2500 to 538.8{{nbsp}}[[Myr|Mya]],<ref name="StratChart 2022">{{cite web |title=Stratigraphic Chart 2022 |url=https://stratigraphy.org/ICSchart/ChronostratChart2022-02.pdf |publisher=International Stratigraphic Commission | date=February 2022 | access-date=22 April 2022}}</ref> the longest eon of the Earth's [[geologic time scale]]. It is preceded by the [[Archean]] and followed by the [[Phanerozoic]], and is the most recent part of the [[Precambrian]] "supereon".

The Proterozoic is subdivided into three [[era (geology)|geologic era]]s (from oldest to youngest): the [[Paleoproterozoic]], [[Mesoproterozoic]] and [[Neoproterozoic]].<ref>{{cite web|last1=Speer|first1=Brian|title=The Proterozoic Eon|url=http://www.ucmp.berkeley.edu/precambrian/proterozoic.php|website=University of California Museum of Paleontology}}</ref> It covers the time from the appearance of free [[oxygen]] in [[Earth's atmosphere]] to just before the proliferation of [[complex life]] on the Earth during the [[Cambrian Explosion]]. The name ''Proterozoic'' combines two forms of ultimately [[Greek language|Greek]] origin: {{lang|grc-Latn|protero-}} meaning "former, earlier", and {{lang|grc-Latn|-zoic}}, meaning "of life".<ref>{{cite web |title=Proterozoic, adj. and n. |url=https://www.eod.com/view/Entry/237724?redirectedFrom=Proterozoic |website=OED Online |publisher=Oxford University Press |access-date=25 June 2021 |date=June 2021}}</ref>

Well-identified events of this eon were the [[Great Oxidation Event|transition to an oxygenated atmosphere]] during the Paleoproterozoic; the evolution of [[eukaryotes]] via [[symbiogenesis]]; several global [[glaciation]]s, which produced the 300 million years-long [[Huronian glaciation]] (during the [[Siderian]] and [[Rhyacian]] periods of the Paleoproterozoic) and the hypothesized [[Snowball Earth]] (during the [[Cryogenian]] period in the late Neoproterozoic); and the [[Ediacaran]] period (635 to 538.8 Ma), which is characterized by the [[evolution]] of abundant soft-bodied [[multicellular organism]]s such as [[sponge]]s, [[algae]], [[cnidarian]]s, [[bilaterian]]s and the sessile [[Ediacaran biota]] (some of which had evolved [[sexual reproduction]]) and provides the first obvious [[fossil]] evidence of [[history of life|life on Earth]].

==The Proterozoic record==
The geologic record of the Proterozoic Eon is more complete than that for the preceding [[Archean]] Eon. In contrast to the deep-water deposits of the Archean, the Proterozoic features many [[stratum|strata]] that were laid down in extensive shallow [[Inland sea (geology)|epicontinental seas]]; furthermore, many of those rocks are less [[Metamorphic rock|metamorphosed]] than Archean rocks, and many are unaltered.<ref name=Stanley>{{cite book| last=Stanley| first=Steven M.| title=Earth System History| location=New York| publisher=W.H. Freeman and Company| year=1999| isbn=978-0-7167-2882-5}}</ref>{{rp|315}} Studies of these rocks have shown that the eon continued the massive [[continent]]al accretion that had begun late in the Archean Eon. The Proterozoic Eon also featured the first definitive [[supercontinent cycle]]s and {{clarify span|text=wholly modern|explain=Compared to partially modern? What is (geologically) modern?|date=April 2023}} mountain building activity ([[orogeny]]).<ref name=Stanley/>{{rp|315–18, 329–32}}

There is evidence that the first known glaciations occurred during the Proterozoic. The first began shortly after the beginning of the Proterozoic Eon, and evidence of at least four during the Neoproterozoic Era at the end of the Proterozoic Eon, possibly climaxing with the hypothesized [[Snowball Earth]] of the [[Sturtian]] and [[Marinoan]] glaciations.<ref name=Stanley/>{{rp|320–1, 325}}

==The accumulation of oxygen==
{{Main|Great Oxidation Event}}
One of the most important events of the Proterozoic was the [[oxygen catastrophe|accumulation of oxygen]] in the Earth's atmosphere. Though oxygen is believed to have been released by [[photosynthesis]] as far back as the Archean Eon, it could not build up to any significant degree until mineral sinks of [[Oxidation|unoxidized]] [[sulfur]] and [[iron]] had been exhausted. Until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level.<ref name=Stanley/>{{rp|323}} The [[banded iron formation]]s, which provide most of the world's [[iron ore]], are one mark of that mineral sink process. Their accumulation ceased after 1.9 billion years ago, after the iron in the oceans had all been oxidized.<ref name=Stanley/>{{rp|324}}

[[Red bed]]s, which are colored by [[hematite]], indicate an increase in atmospheric oxygen 2 billion years ago. Such massive iron oxide formations are not found in older rocks.<ref name=Stanley/>{{rp|324}} The oxygen buildup was probably due to two factors: exhaustion of the chemical sinks, and an increase in [[carbon sequestration]], which sequestered [[organic compound]]s that would have otherwise been oxidized by the atmosphere.<ref name=Stanley/>{{rp|325}}

A second surge in oxygen concentrations, known as the [[Neoproterozoic Oxygenation Event]],<ref name="Shields-Zhou2011">{{cite journal |last1=Shields-Zhou |first1=Graham A. |last2=Och |first2=Lawrence M. |date=March 2011 |title=The case for a Neoproterozoic Oxygenation Event: Geochemical evidence and biological consequences |url=https://discovery.ucl.ac.uk/id/eprint/1354478/1/1354478_Shields-Zhou%2520and%2520Och_2011.pdf |journal=GSA Today |volume=21 |issue=3 |pages=4–11 |doi=10.1130/GSATG102A.1 |access-date=10 November 2022}}</ref> occurred during the Middle and Late Neoproterozoic<ref name="Och2012">{{cite journal |last1=Och |first1=Lawrence M. |last2=Shields-Zhou |first2=Graham A. |date=January 2012 |title=The Neoproterozoic oxygenation event: Environmental perturbations and biogeochemical cycling |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825211001498 |journal=[[Earth-Science Reviews]] |volume=110 |issue=1–4 |pages=26–57 |doi=10.1016/j.earscirev.2011.09.004 |access-date=10 November 2022}}</ref> and drove the rapid evolution of multicellular life towards the end of the era.<ref>{{cite journal |last1=Canfield |first1=Donald Eugene |last2=Poulton |first2=Simon W. |last3=Narbonne |first3=Guy M. |date=5 January 2007 |title=Late-Neoproterozoic Deep-Ocean Oxygenation and the Rise of Animal Life |url=https://www.science.org/doi/10.1126/science.1135013 |journal=Science |volume=315 |issue=5808 |pages=92–95 |doi=10.1126/science.1135013 |pmid=17158290 |s2cid=24761414 |access-date=10 November 2022}}</ref><ref name="EdiacaranOxygenationIronIsotopes">{{cite journal |last1=Fan |first1=Haifeng |last2=Zhu |first2=Xiangkun |last3=Wen |first3=Hanjie |last4=Yan |first4=Bin |last5=Li |first5=Jin |last6=Feng |first6=Lianjun |date=1 September 2014 |title=Oxygenation of Ediacaran Ocean recorded by iron isotopes |url=https://www.sciencedirect.com/science/article/abs/pii/S0016703714003585 |journal=[[Geochimica et Cosmochimica Acta]] |volume=140 |pages=80–94 |doi=10.1016/j.gca.2014.05.029 |access-date=10 November 2022}}</ref>

==Subduction processes==
The Proterozoic Eon was a very tectonically active period in the Earth's history.

The late Archean Eon to Early Proterozoic Eon corresponds to a period of increasing crustal recycling, suggesting [[subduction]]. Evidence for this increased subduction activity comes from the abundance of old granites originating mostly after 2.6 Ga.<ref name=Kearey>{{cite book |last1=Kearey |first1=P. |last2=Klepeis |first2=K. |last3=Vine |first3=F. |title=Precambrian Tectonics and the Supercontinent Cycle |series=Global Tectonics |edition=Third |pages=361–377 |year=2008}}</ref>

The occurrence of [[eclogite]] (a type of [[metamorphic rock]] created by high pressure, > 1 GPa), is explained using a model that incorporates subduction. The lack of eclogites that date to the Archean Eon suggests that conditions at that time did not favor the formation of high grade metamorphism and therefore did not achieve the same levels of subduction as was occurring in the Proterozoic Eon.<ref>{{cite journal |last=Bird |first=P. |title=An updated digital model of plate boundaries|journal=Geochemistry, Geophysics, Geosystems |year=2003 |volume=4 |issue=3 |pages=1027 |doi=10.1029/2001GC000252 |bibcode=2003GGG.....4.1027B|doi-access=free }}</ref>

As a result of remelting of [[basalt]]ic [[oceanic crust]] due to subduction, the cores of the first continents grew large enough to withstand the crustal recycling processes.

The long-term tectonic stability of those [[craton]]s is why we find [[continental crust]] ranging up to a few billion years in age.<ref>{{cite book |last=Mengel |first=F. |title=Proterozoic History |series=Earth System: History and Variablility |volume=2 |year=1998}}</ref> It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, and only 18% in the [[Phanerozoic]].<ref name=Kearey/> Studies by Condie (2000)<ref>Condie, K. (2000). Episodic continental growth models: afterthoughts and extensions. ''Tectonophysics'', ''322''(1), 153–162. {{doi|10.1016/S0040-1951(00)00061-5}}</ref> and Rino et al. (2004)<ref>{{cite journal |last1=Rino |first1=Shuji |last2=Komiya |first2=Tsuyoshi |last3=Windley |first3=Brian F. |last4=Katayama |first4=Ikuo |last5=Motoki |first5=Akihisa |last6=Hirata |first6=Takafumi |title=Major episodic increases of continental crustal growth determined from zircon ages of river sands; implications for mantle overturns in the Early Precambrian |journal=Physics of the Earth and Planetary Interiors |date=August 2004 |volume=146 |issue=1–2 |pages=369–394 |doi=10.1016/j.pepi.2003.09.024|bibcode=2004PEPI..146..369R |s2cid=140166194 }}</ref> suggest that crust production happened episodically. By isotopically calculating the ages of Proterozoic granitoids it was determined that there were several episodes of rapid increase in continental crust production. The reason for these pulses is unknown, but they seemed to have decreased in magnitude after every period.<ref name=Kearey/>

{{clear}}

==Tectonic history (supercontinents)==

<gallery>
File:Paleoglobe NO 1590 mya-vector-colors.svg|[[Columbia (supercontinent)|Columbia]], about 1,590 Mya
File:Rodinia reconstruction.jpg|[[Rodinia]], about 750 Mya
File:Pannotia.svg|[[Pannotia]], 545 Mya (disputed{{clarify|date=June 2023}}), centered on South Pole
File:Gondwana 420 Ma.png|[[Gondwana]] 420 Mya, centered on South Pole
</gallery>

Evidence of collision and rifting between continents raises the question as to what exactly were the movements of the Archean cratons composing Proterozoic continents. [[Paleomagnetism|Paleomagnetic]] and geochronological dating mechanisms have allowed the deciphering of Precambrian Supereon tectonics. It is known that tectonic processes of the Proterozoic Eon resemble greatly the evidence of tectonic activity, such as [[orogenic belt]]s or [[ophiolite]] complexes, we see today. Hence, most geologists would conclude that the Earth was active at that time. It is also commonly accepted that during the Precambrian, the Earth went through several supercontinent breakup and rebuilding cycles ([[Wilson cycle]]).<ref name=Kearey/>

In the late Proterozoic (most recent), the dominant supercontinent was [[Rodinia]] (~1000–750 Ma). It consisted of a series of continents attached to a central craton that forms the core of the North American Continent called [[Laurentia]]. An example of an orogeny (mountain building processes) associated with the construction of Rodinia is the [[Grenville orogeny]] located in Eastern North America. Rodinia formed after the breakup of the supercontinent [[Columbia (supercontinent)|Columbia]] and prior to the assemblage of the supercontinent [[Gondwana]] (~500 Ma).<ref>{{cite journal |last1=Condie |first1=K. C. |last2=O'Neill |first2=C. |title=The Archean-Proterozoic boundary: 500 my of tectonic transition in Earth history |journal=American Journal of Science |date=2011 |volume=310 |issue=9 |pages=775–790 |doi=10.2475/09.2010.01 |bibcode=2010AmJS..310..775C|s2cid=128469935 |doi-access=free }}</ref> The defining orogenic event associated with the formation of Gondwana was the collision of Africa, South America, Antarctica and Australia forming the [[Pan-African orogeny]].<ref>{{cite book |last=Huntly |first=C. |title=The Mozambique Belt, Eastern Africa: Tectonic evolution of the Mozambique Ocean and Gondwana amalgamation |publisher=The Geological Society of America |year=2002}}</ref>

[[Columbia (supercontinent)|Columbia]] was dominant in the early-mid Proterozoic and not much is known about continental assemblages before then. There are a few plausible models that explain tectonics of the early Earth prior to the formation of Columbia, but the current most plausible hypothesis is that prior to Columbia, there were only a few independent cratons scattered around the Earth (not necessarily a supercontinent, like Rodinia or Columbia).<ref name=Kearey/>

==Life==

The emergence of advanced single-celled [[eukaryotes]] began after the [[Great Oxidation Event]].<ref>{{Cite journal |last1=Fakhraee |first1=Mojtaba |last2=Tarhan |first2=Lidya G. |last3=Reinhard |first3=Christopher T. |last4=Crowe |first4=Sean A. |last5=Lyons |first5=Timothy W. |last6=Planavsky |first6=Noah J. |date=May 2023 |title=Earth's surface oxygenation and the rise of eukaryotic life: Relationships to the Lomagundi positive carbon isotope excursion revisited |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825223000879 |journal=Earth-Science Reviews |language=en |volume=240 |pages=104398 |doi=10.1016/j.earscirev.2023.104398|s2cid=257761993 }}</ref> This may have been due to an increase in the oxidized [[nitrate]]s that eukaryotes use, as opposed to [[cyanobacteria]].<ref name=Stanley/>{{rp|325}} It was also during the Proterozoic that the first [[symbiosis|symbiotic]] relationships between [[mitochondria]] (found in nearly all eukaryotes) and [[chloroplast]]s (found in [[plant]]s and some [[protist]]s only) and their hosts evolved.<ref name=Stanley/>{{rp|321–2}}

By the late Palaeoproterozoic, eukaryotic organisms had become moderately biodiverse.<ref>{{cite journal |last1=Miao |first1=Lanyun |last2=Moczydłowska |first2=Małgorzata |last3=Zhu |first3=Shixing |last4=Zhu |first4=Maoyan |date=February 2019 |title=New record of organic-walled, morphologically distinct microfossils from the late Paleoproterozoic Changcheng Group in the Yanshan Range, North China |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926818301827 |journal=[[Precambrian Research]] |volume=321 |pages=172–198 |doi=10.1016/j.precamres.2018.11.019 |s2cid=134362289 |access-date=29 December 2022}}</ref> The blossoming of eukaryotes such as [[acritarch]]s did not preclude the expansion of cyanobacteria; in fact, [[stromatolites]] reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1200 million years ago.<ref name=Stanley/>{{rp|321–3}}

The earliest [[fossil]]s possessing features typical of [[Fungus|fungi]] date to the [[Paleoproterozoic]] Era, some 2,400 million years ago; these multicellular [[benthic]] organisms had filamentous structures capable of [[anastomosis]].<ref>{{Cite journal|last1=Bengtson|first1=Stefan|last2=Rasmussen|first2=Birger|last3=Ivarsson|first3=Magnus|last4=Muhling|first4=Janet|last5=Broman|first5=Curt|last6=Marone|first6=Federica|last7=Stampanoni|first7=Marco|last8=Bekker|first8=Andrey|date=2017-04-24|title=Fungus-like mycelial fossils in 2.4-billion-year-old vesicular basalt.|url=https://escholarship.org/uc/item/4883d4qh|journal=Nature Ecology & Evolution|language=en|volume=1|issue=6|pages=141|doi=10.1038/s41559-017-0141|pmid=28812648|hdl=20.500.11937/67718 |s2cid=25586788|issn=2397-334X|hdl-access=free}}</ref>

Classically, the boundary between the Proterozoic and the [[Phanerozoic]] eons was set at the base of the [[Cambrian]] [[period (geology)|Period]] when the first fossils of animals, including [[trilobite]]s and [[archaeocyatha|archeocyathids]], as well as the animal-like ''[[Caveasphaera]]'', appeared. In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, particularly in ones from the Ediacaran, proving that multicellular life had already become widespread tens of millions of years before the [[Cambrian explosion|Cambrian Explosion]] in what is known as the [[Avalon explosion|Avalon Explosion]].<ref name="OnTheEveOfAnimalRadiation">{{cite journal |last1=Xiao |first1=Shuhai |last2=Laflamme |first2=Marc |date=January 2009 |title=On the eve of animal radiation: phylogeny, ecology and evolution of the Ediacara biota |url=https://www.sciencedirect.com/science/article/abs/pii/S0169534708003066 |journal=[[Trends in Ecology & Evolution]] |volume=24 |issue=1 |pages=31–40 |doi=10.1016/j.tree.2008.07.015 |pmid=18952316 |access-date=10 November 2022}}</ref> Nonetheless, the upper boundary of the Proterozoic has remained fixed at the base of the Cambrian, which is currently placed at 538.8 Ma.
{{clear}}

==See also==
{{Life timeline}}
* [[Boring Billion]]
* [[Timeline of natural history]]
*[[Volyn biota]]

==References==
{{reflist|25em}}

==External links==
{{commons category}}
* [https://web.archive.org/web/20070702223746/http://www.palaeos.com/Proterozoic/Proterozoic.htm Palaeos.com: Proterozoic eon]
* [https://ghkclass.com/ghkC.html?proterozoic Proterozoic (chronostratigraphy scale)]

{{Geological history|c|state=collapsed}}
{{Authority control}}

[[Category:Proterozoic| ]]
[[Category:Precambrian geochronology|*03]]

Proterozoic - Revision history

Ajay Kumar: Created a new article