View source for Great Oxidation Event

{{short description|Paleoproterozoic surge in atmospheric oxygen}}
{{about|the prehistoric event|the hypothetical use of nanotechnology sometimes called "green goo"|Glossary of nanotechnology#G}}
{{Use dmy dates|date=July 2013}}
[[Image:Oxygenation-atm-2.svg|thumb|upright=2|O<sub>2</sub> build-up in the [[Earth's atmosphere]]. Red and green lines represent the range of the estimates while time is measured in billions of years ago (Ga).
<br />Stage 1 (3.85–2.45 Ga): Practically no O<sub>2</sub> in the atmosphere. The oceans were also largely anoxic with the possible exception of O<sub>2</sub> in the shallow oceans.
<br />Stage 2 (2.45–1.85 Ga): O<sub>2</sub> produced, rising to values of 0.02 and 0.04 atm, but absorbed in oceans and seabed rock.
<br />Stage 3 (1.85–0.85 Ga): O<sub>2</sub> starts to gas out of the oceans, but is absorbed by land surfaces. No significant change in oxygen level.
<br />Stages 4 and 5 (0.85 Ga–present): Other O<sub>2</sub> reservoirs filled; gas accumulates in atmosphere.<ref>{{cite journal |author=Holland, Heinrich D. |title=The oxygenation of the atmosphere and oceans |journal=Philosophical Transactions of the Royal Society: Biological Sciences |volume=361 |year=2006 |issue=1470 |pages=903–915 |doi=10.1098/rstb.2006.1838|pmid=16754606 |pmc=1578726 }}</ref>]]

The '''Great Oxidation Event''' ('''GOE'''), sometimes also called the '''Great Oxygenation Event''', '''Oxygen Catastrophe''', '''Oxygen Crisis''', '''Oxygen Holocaust''',<ref>{{cite book |title=Microcosmos: Four Billion Years of Microbial Evolution |last1=Margulis |first1=Lynn |last2=Sagan |first2=Dorion |publisher=University of California Press |year=1986 |isbn=9780520210646 |location=California |page=99 |chapter=Chapter 6, "The Oxygen Holocaust" |author-link1=Lynn Margulis |author-link2=Dorion Sagan |chapter-url=https://books.google.com/books?id=eo_sMMRxgAUC&lpg=PA99&dq=oxygen%20holocaust&pg=PA99#v=onepage}}</ref> or '''Oxygen Revolution''', was a time period when the [[Atmosphere of Earth|Earth's atmosphere]] and the shallow ocean experienced a rise in oxygen, approximately 2.4&nbsp;billion years ago (2.4&nbsp;[[Year#SI prefix multipliers|Ga]]) to 2.1–2.0 Ga during the [[Paleoproterozoic]] era.<ref name="Lyons 307–315">{{Cite journal |last1=Lyons |first1=Timothy W. |last2=Reinhard |first2=Christopher T. |last3=Planavsky |first3=Noah J. |date=February 2014 |title=The rise of oxygen in Earth's early ocean and atmosphere |journal=Nature |volume=506 |issue=7488 |pages=307–315 |doi=10.1038/nature13068 |pmid=24553238 |issn=0028-0836 |bibcode=2014Natur.506..307L}}</ref> Geological, [[Isotope|isotopic]], and chemical evidence suggests that [[Biota (ecology)|biologically]] produced molecular oxygen ([[Oxygen#Allotropes|dioxygen]], O<sub>2</sub>) started to accumulate in Earth's atmosphere and changed Earth's atmosphere from a weakly [[reducing atmosphere]] to an oxidizing atmosphere, <ref>{{cite book |title=Sustaining Life on Planet Earth: Metalloenzymes Mastering Dioxygen and Other Chewy Gases |last1=Sosa Torres |first1=Martha E. |last2=Saucedo-Vázquez |first2=Juan P. |last3=Kroneck |first3=Peter M.H. |publisher=Springer|year=2015 |isbn=978-3-319-12414-8 |editor1=Kroneck, Peter M.H. |editor2=Sosa Torres, Martha E. |series=Metal Ions in Life Sciences |volume=15 |pages=1–12|chapter=Chapter 1, Section 2: The rise of dioxygen in the atmosphere |doi=10.1007/978-3-319-12415-5_1 |pmid=25707464}}</ref> causing many existing species on Earth to die out.<ref>{{cite journal |last1=Hodgskiss |first1=Malcolm S.W. |last2=Crockford |first2=Peter W. |last3=Peng |first3=Yongbo |last4=Wing |first4=Boswell A. |last5=Horner |first5=Tristan J. |title=A productivity collapse to end Earth's Great Oxidation |journal=PNAS |date=August 27, 2019 |df=dmy-all |volume=116 |issue=35 |pages=17207–17212 |doi=10.1073/pnas.1900325116 |pmid=31405980 |pmc=6717284|bibcode=2019PNAS..11617207H }}</ref> The [[cyanobacteria]] producing the oxygen caused the event which enabled the subsequent development of [[multicellular]] forms.<ref>{{cite news |url=https://www.sciencedaily.com/releases/2013/01/130117084856.htm |author=University of Zurich |title=Great Oxidation Event: More oxygen through multicellularity |work=ScienceDaily |date=17 January 2013 |access-date=27 August 2019}}</ref>

==Oxygen accumulation==
{{see also|Oxygen cycle}}
{{Life timeline}}
A chronology of oxygen accumulation suggests that free oxygen was first produced by [[Prokaryote| prokaryotic]] and then later by [[eukaryotic]] organisms in the ocean. These organisms carried out [[photosynthesis]] more efficiently,{{Compared to?|date=November 2019}} producing oxygen as a waste product.<ref name=":2">{{cite web |url=http://www.astrobio.net/news-exclusive/the-rise-of-oxygen/ |title=The Rise of Oxygen |website=Astrobiology Magazine |date=30 July 2003 |access-date=2016-04-06 |df=dmy-all}}</ref><ref>{{cite web |url=https://uwaterloo.ca/science/news/researchers-discover-when-and-where-oxygen-began-its-rise |title=Researchers discover when and where oxygen began its rise |date=March 2019 |publisher=University of Waterloo |department=Science News |access-date=6 July 2020 |archive-date=24 April 2019 |archive-url=https://web.archive.org/web/20190424200402/https://uwaterloo.ca/science/news/researchers-discover-when-and-where-oxygen-began-its-rise }}</ref> In one interpretation, the first oxygen-producing [[cyanobacteria]] could have arisen before the GOE,<ref name=":2" /><ref>{{cite journal |last1=Dutkiewicz |first1=A. |last2=Volk |first2=H. |last3=George |first3=S.C. |last4=Ridley |first4=J. |last5=Buick |first5=R. |year=2006 |title=Biomarkers from Huronian oil-bearing fluid inclusions: An uncontaminated record of life before the Great Oxidation Event |journal=Geology |volume=34 |issue=6 |pages=437 |bibcode= 2006Geo....34..437D |doi=10.1130/G22360.1}}</ref> from 2.7–2.4&nbsp;Ga and perhaps even earlier.<ref name="Lyons 307–315"/><ref name="ELSVR-201803062">{{cite journal |last=Caredona |first=Tanai |date=6 March 2018 |title=Early Archean origin of heterodimeric Photosystem&nbsp;I |journal=[[Elsevier (magazine)|Elsevier]] |volume=4 |issue=3 |page=e00548 |doi=10.1016/j.heliyon.2018.e00548 |pmid=29560463 |pmc=5857716}}</ref><ref name="AST-201803072">{{cite web |last=Howard |first=Victoria |title=Photosynthesis originated a billion years earlier than we thought, study shows |url=https://www.astrobio.net/also-in-news/photosynthesis-originated-billion-years-earlier-thought-study-shows/ |date=7 March 2018 |work=[[Astrobiology Magazine]] |accessdate=23 March 2018}}</ref> However, oxygenic photosynthesis also produces organic carbon that must be segregated from oxygen to allow oxygen accumulation in the surface environment, otherwise the oxygen back-reacts with the organic carbon and does not accumulate. The burial of organic carbon, sulfide, and minerals containing [[ferrous]] iron (Fe{{sup|2+}}) is a primary factor in oxygen accumulation.<ref name=":0"/> For example, when organic carbon is buried without being oxidized, the oxygen is left in the atmosphere. In total, the burial of organic carbon and pyrite today creates {{nowrap|15.8 ± 3.3 [[Tera-|T]] mol}} {{nowrap|(1 T mol {{=}} 10<sup>12</sup> moles)}} of O{{sub|2}} per year. This creates a net O{{sub|2}} flux from the global oxygen sources. Test123.

The rate of change of oxygen can be calculated from the difference between global sources and sinks.<ref name=":02">{{Cite book |title=Atmospheric Evolution on Inhabited and Lifeless Worlds |last1=Catling |first1=David C. |last2=Kasting |first2=James F. |date=2017 |publisher=Cambridge University Press |isbn=9781139020558 |location=Cambridge |doi=10.1017/9781139020558}}</ref> The oxygen sinks include reduced gases and minerals from volcanoes, metamorphism and weathering.<ref name=":02"/> The GOE started after these oxygen-sink fluxes and reduced-gas fluxes were exceeded by the flux of O<sub>2</sub> associated with the burial of reductants, such as organic carbon.<ref name=":1">{{cite web |url=https://www.sciencedaily.com/releases/2013/01/130117084856.htm |author=University of Zurich |title=Great Oxidation Event: More oxygen through multicellularity |date=17 January 2013 |website=ScienceDaily}}</ref> For the weathering mechanisms, {{nowrap|12.0 ± 3.3 T mol}} of O{{sub|2}} per year today goes to the sinks composed of reduced minerals and gases from volcanoes, metamorphism, percolating seawater and heat vents from the seafloor.<ref name=":02"/> On the other hand, {{nowrap|5.7 ± 1.2 T mol}} of O{{sub|2}} per year today oxidizes reduced gases in the atmosphere through photochemical reaction.<ref name=":02" /> On the early Earth, there was visibly very little oxidative weathering of continents (e.g., a lack of [[Red beds| redbeds]]) and so the weathering sink on oxygen would have been negligible compared to that from reduced gases and dissolved iron in oceans.

Dissolved iron in oceans exemplifies O<sub>2</sub> sinks. Free oxygen produced during this time was chemically captured by [[Banded iron formation#Origins |dissolved iron]], converting iron <chem>Fe</chem> and <chem>Fe^2+</chem> to [[magnetite]] (<chem>Fe^2+Fe2^3+O4</chem>) that is insoluble in water, and sank to the bottom of the shallow seas to create [[banded iron formation]]s such as the ones found in Minnesota and [[Pilbara]], Western Australia.<ref name=":1"/> It took 50&nbsp;million years or longer to deplete the oxygen sinks.<ref name="Anabar20072">{{cite journal |last1=Anbar |first1=A. |last2=Duan |first2=Y. |last3=Lyons |first3=T. |last4=Arnold |first4=G. |last5=Kendall |first5=B. |last6=Creaser |first6=R. |last7=Kaufman |first7=A. |last8=Gordon |first8=G. |last9=Scott |first9=C. |first10=J. |last10=Garvin |last11=Buick |first11=R. |year=2007 |title=A whiff of oxygen before the great oxidation event? |journal=Science |volume=317 |issue=5846 |pages=1903–1906 |bibcode=2007Sci...317.1903A |doi=10.1126/science.1140325 |pmid=17901330}}</ref> The rate of photosynthesis and associated rate of organic burial also affect the rate of oxygen accumulation. When land plants spread over the continents in the [[Devonian]], more organic carbon was buried and likely allowed higher O<sub>2</sub> levels to occur.<ref>{{cite journal |last1=Dahl |first1=T.W. |last2=Hammarlund |first2=E.U. |last3=Anbar |first3=A.D. |last4=Bond |first4=D.P.G. |last5=Gill |first5=B.C. |last6=Gordon |first6=G.W. |last7=Knoll |first7=A.H. |last8=Nielsen |first8=A.T. |last9=Schovsbo |first9=N.H. |date=2010-09-30 |df=dmy-all |title=Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish |journal=Proceedings of the National Academy of Sciences |volume=107 |issue=42 |pages=17911–17915 |doi=10.1073/pnas.1011287107 |pmid=20884852 |issn=0027-8424 |pmc=2964239 |bibcode=2010PNAS..10717911D}}</ref> Today, the average time that an O{{sub|2}} molecule spends in the air before it is consumed by geological sinks is about 2&nbsp;million years.<ref>{{Cite journal |last1=Catling |first1=David C. |last2=Claire |first2=Mark W. |date=August 2005 |title=How Earth's atmosphere evolved to an oxic state: A status report |journal=Earth and Planetary Science Letters |volume=237 |issue=1–2 |pages=1–20 |doi=10.1016/j.epsl.2005.06.013 |issn=0012-821X |bibcode=2005E&PSL.237....1C }}</ref> That residence time is relatively short compared to geologic time - so in the [[Phanerozoic]] there must have been feedback processes that kept the atmospheric O{{sub|2}} level within bounds suitable for animal life.

Eventually, oxygen started to accumulate in the atmosphere, with two major consequences.

* First, it has been proposed that oxygen oxidized [[atmospheric methane]] (a strong [[greenhouse gas]]) to carbon dioxide (a weaker one) and water. This weakened the [[greenhouse effect]] of the Earth's atmosphere, causing planetary cooling, which has been proposed to have triggered a series of ice ages known as the [[Huronian glaciation]], bracketing an age range of 2.45–2.22&nbsp;Ga.<ref>{{Cite encyclopedia |last=Bekker |first=Andrey |chapter=Huronian Glaciation |year=2014 |encyclopedia=Encyclopedia of Astrobiology |pages=1–8 |editor-last=Amils |editor-first=Ricardo |publisher=Springer Berlin Heidelberg |doi=10.1007/978-3-642-27833-4_742-4 |isbn=9783642278334 |df=dmy-all |editor2-last=Gargaud |editor2-first=Muriel |editor3-last=Cernicharo Quintanilla |editor3-first=José |editor4-last=Cleaves |editor4-first=Henderson James}}</ref><ref name="Kopp20052">{{Cite journal |author1=Kopp, Robert E. |author2=Kirschvink, Joseph L. |author3=Hilburn, Isaac A. |author4=Nash, Cody Z. |date=2005 |title=The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis |url=http://www.pnas.org/cgi/reprint/0504878102v1 |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=102 |issue=32 |pages=11131–11136 |bibcode=2005PNAS..10211131K |doi=10.1073/pnas.0504878102 |pmc=1183582 |pmid=16061801 |access-date=6 July 2020 |archive-date=8 January 2008 |archive-url=https://web.archive.org/web/20080108045031/http://www.pnas.org/cgi/reprint/0504878102v1 |url-status=dead }}</ref><ref name="NS2">{{cite magazine |url=https://www.newscientist.com/article/mg20527461.100-first-breath-earths-billionyear-struggle-for-oxygen.html |title=First breath: Earth's billion-year struggle for oxygen |magazine=New Scientist |issue=2746 |date=5 February 2010 |first=Nick |last=Lane}}</ref> A fourth glaciation event found in South Africa is ~2.22&nbsp;Ga in age. Because geological evidence suggests that the ice reached sea-level in some areas and that the South African event occurred at low latitudes, the latter is associated with a so-called [[Snowball Earth]].<ref>{{cite journal |last1=Evans |first1=D.A. |last2=Beukes |first2=N.J. |last3=Kirschvink |first3=J.L. |date=March 1997 |title=Low-latitude glaciation in the Palaeoproterozoic era |journal=Nature |volume=386 |issue=6622 |pages=262–266 |doi= 10.1038/386262a0 |issn=0028-0836 |bibcode=1997Natur.386..262E}}</ref>

* Second, the increased oxygen concentrations provided a new opportunity for [[Evolution| biological diversification]], as well as tremendous changes in the nature of chemical interactions between [[Rock (geology) |rocks]], [[sand]], [[clay]], and other geological substrates and the Earth's air, oceans, and other surface waters. Despite the natural recycling of [[organic matter]], life had remained energetically limited until the widespread availability of oxygen. This breakthrough in metabolic evolution greatly increased the [[Thermodynamic free energy |free energy]] available to living organisms, with global environmental impacts. For example, [[mitochondria]] evolved after the GOE, giving organisms the energy to exploit new, more complex morphology interacting in increasingly complex ecosystems, although these did not appear until the late Proterozoic and Cambrian.<ref>{{cite journal |last1=Sperling |first1=Erik |last2=Frieder |first2=Christina |last3=Raman |first3=Akkur |last4=Girguis |first4=Peter |last5=Levin |first5=Lisa |last6= Knoll |first6=Andrew |date=Aug 2013 |title=Oxygen, ecology, and the Cambrian radiation of animals |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=110 |issue=33 |pages=13446–13451 |bibcode=2013PNAS..11013446S |doi=10.1073/pnas.1312778110 |pmc=3746845 |pmid=23898193}}</ref>

{{clear}}

[[File:GlaciationsinEarthExistancelicenced annotated.jpg |thumb|upright=3.5|center| Timeline of glaciations, shown in blue.]]

{{clear}}

== Geological evidence ==

=== Continental indicators ===
[[Paleosol]]s, [[Detritus (geology)|detrital]] grains, and [[Red beds|redbeds]] are evidence of low-level oxygen.<ref name=":02"/> {{verify source |reason=This was improperly placed in the heading. I don't know what it was supposed to support |date=August 2019}} The paleosols older than 2.4&nbsp;Ga have low iron concentrations that suggests anoxic weathering.<ref>{{cite journal |last1=Utsunomiya |first1=Satoshi |last2=Murakami |first2=Takashi |last3=Nakada |first3=Masami |last4=Kasama |first4=Takeshi |date=January 2003 |title=Iron oxidation state of a 2.45&nbsp;Byr-old paleosol developed on mafic volcanics |journal=Geochimica et Cosmochimica Acta |volume=67 |issue=2 |pages=213–221 |doi=10.1016/s0016-7037(02)01083-9 |issn=0016-7037 |bibcode=2003GeCoA..67..213U}}</ref> [[Detritus (geology)|Detrital]] grains older than 2.4&nbsp;Ga also have material that only exists under low oxygen conditions.<ref>{{Cite journal |last1=Hofmann |first1=Axel |last2=Bekker |first2=Andrey |last3=Rouxel |first3=Olivier |last4=Rumble |first4=Doug |last5=Master |first5=Sharad |date=September 2009 |title=Multiple sulphur and iron isotope composition of detrital pyrite in Archaean sedimentary rocks: A new tool for provenance analysis |journal=Earth and Planetary Science Letters |volume=286 |issue=3–4 |pages=436–445 |doi=10.1016/j.epsl.2009.07.008 |issn=0012-821X |bibcode=2009E&PSL.286..436H |hdl=1912/3068 |url=https://darchive.mblwhoilibrary.org/bitstream/1912/3068/1/manuscript_revised_with_figs.pdf}}</ref> [[Red beds|Redbeds]] are red-colored [[sandstone]]s that are coated with [[hematite]], which indicates that there was enough oxygen to oxidize iron.<ref>{{cite journal |last1=Eriksson |first1=Patrick G. |last2=Cheney |first2=Eric S. |date=January 1992 |title=Evidence for the transition to an oxygen-rich atmosphere during the evolution of red beds in the lower proterozoic sequences of southern Africa |journal=Precambrian Research |volume=54 |issue=2–4 |pages=257–269 |doi=10.1016/0301-9268(92)90073-w |issn=0301-9268 |bibcode=1992PreR...54..257E}}</ref>

=== Banded iron formation (BIF) ===
{{see also|Banded iron formation}}

=== Iron speciation ===
The concentration of [[wikt:ferruginous|ferruginous]] and [[Euxinia|euxinic]] states in iron mass can also provide clues of the oxygen level in the atmosphere.<ref>{{cite journal |last1=Lyons |first1=Timothy W. |last2=Anbar |first2=Ariel D. |last3=Severmann |first3=Silke |last4=Scott |first4=Clint |last5=Gill |first5=Benjamin C. |date=May 2009 |title=Tracking Euxinia in the Ancient Ocean: A Multiproxy Perspective and Proterozoic Case Study |journal=Annual Review of Earth and Planetary Sciences |volume=37 |issue=1 |pages=507–534 |doi=10.1146/annurev.earth.36.031207.124233 |issn=0084-6597 |bibcode=2009AREPS..37..507L}}</ref>{{verify source |reason=This was improperly placed in the heading. I don't know what it was supposed to support |date=August 2019}} When the environment is anoxic, the ratio of ferruginous and euxinic out of the total iron mass is lower than the ratio in an anoxic environment such as the deep ocean.<ref name=":3">{{cite journal |last1=Canfield |first1=Donald E. |last2=Poulton |first2=Simon W. |date=2011-04-01 |df=dmy-all |title=Ferruginous Conditions: A Dominant Feature of the Ocean through Earth's History |journal=Elements |volume=7 |issue=2 |pages=107–112 |doi=10.2113/gselements.7.2.107 |issn=1811-5209}}</ref> One of the hypotheses suggests that microbes in the ocean already oxygenated the shallow waters before the GOE event around 2.6–2.5&nbsp;Ga.<ref name=":02"/><ref name=":3"/> The high concentration of ferruginous and euxinic states of sediments in the deep ocean showed consistency with the evidence from banded iron formations.<ref name=":02"/>

=== Isotopes ===
There are two types of isotope fractionation considered: [[mass-dependent fractionation]] (MDF) and [[mass-independent fractionation]] (MIF). Isotopes in marine sediments of the accumulation of oxygen such as carbon, sulfur, nitrogen, transitional metals ([[chromium]], [[molybdenum]] and iron) and other non-metal elements ([[selenium]]) are considered as MDF evidence.<ref name=":02"/>

For example, a spike in chromium contained in ancient rock deposits formed underwater shows accumulated chromium washed off from the continental shelves.<ref name="Frei20093">{{cite journal |last1=Frei |first1=R. |last2=Gaucher |first2=C. |last3=Poulton |first3=S.W. |last4=Canfield |first4=D.E. |year=2009 |title=Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes |journal=Nature |volume=461 |issue=7261 |pages=250–253 |bibcode=2009Natur.461..250F |doi=10.1038/nature08266 |pmid=19741707 |lay-url=https://dx.doi.org/10.1038/461179a}}</ref> Since chromium is not easily dissolved, its release from rocks requires the presence of a powerful acid such as [[sulfuric acid]] (H<sub>2</sub>SO<sub>4</sub>) which may have formed through bacterial reactions with pyrite.<ref>{{cite web |url=http://www.livescience.com/16714-oxygen-breathing-life-chromium.html |title=Evidence of Earliest Oxygen-Breathing Life on Land Discovered |website=LiveScience.com |access-date=2016-04-06 |df=dmy-all}}</ref>

The critical evidence of GOE was the MIF of sulfur isotopes that only existed in anoxic atmosphere and disappeared from sediment rocks after 2.4–2.3&nbsp;Ga.<ref>{{Cite journal|last=Farquhar |first=J. |s2cid=12287304 |date=2000-08-04 |df=dmy-all |title=Atmospheric Influence of Earth's Earliest Sulfur Cycle |journal=Science |volume=289 |issue=5480 |pages=756–758 |doi=10.1126/science.289.5480.756 |pmid=10926533|issn=0036-8075 |bibcode=2000Sci...289..756F }}</ref> MIF only existed in an anoxic atmosphere since oxygen (and its photochemical product, an ozone layer) would have prevented the photolysis of sulfur dioxide. The process of MIF sedimentation is currently uncertain.<ref name=":02" />

=== Fossils and biomarkers ===
{{see also|Biomarker}}
[[Stromatolite]]s provide some of the fossil evidence of oxygen, and suggest that the oxygen came from photosynthesis. [[Biomarker]]s such as 2α-methylhopanes from cyanobacteria were also found in [[Pilbara]], Western Australia. However, the biomarker data has since been shown to have been contaminated and so results are no longer accepted.<ref>{{Cite journal |last1=French |first1=Katherine L. |last2=Hallmann |first2=Christian |last3=Hope |first3=Janet M. |last4=Schoon |first4=Petra L. |last5=Zumberge |first5=J. Alex |last6=Hoshino |first6=Yosuke |last7=Peters |first7=Carl A. |last8=George |first8=Simon C. |last9=Love |first9=Gordon D. |date=2015-04-27 |df=dmy-all |title=Reappraisal of hydrocarbon biomarkers in Archean rocks |journal=Proceedings of the National Academy of Sciences |volume=112 |issue=19 |pages=5915–5920 |doi=10.1073/pnas.1419563112 |pmid=25918387 |issn=0027-8424|pmc=4434754 |bibcode=2015PNAS..112.5915F}}</ref>

=== Other indicators ===
Some elements in marine sediments are sensitive to different levels of oxygen in the environment such as [[transition metal]]s [[molybdenum]] and [[rhenium]].<ref>{{Cite journal |last1=Anbar |first1=Ariel D. |last2=Rouxel |first2=Olivier |s2cid=130960654 |date=May 2007 |title=Metal Stable Isotopes in Paleoceanography |journal=Annual Review of Earth and Planetary Sciences |volume=35 |issue=1 |pages=717–746 |doi=10.1146/annurev.earth.34.031405.125029 |issn=0084-6597 |bibcode=2007AREPS..35..717A }}</ref> Non-metal elements such as [[selenium]] and iodine are also indicators of oxygen levels.<ref>{{cite journal |last1=Stüeken |first1=E.E. |last2=Buick |first2=R. |last3=Bekker |first3=A. |last4=Catling|first4=D. |last5=Foriel |first5=J. |last6=Guy |first6=B.M. |last7=Kah |first7=L.C. |last8=Machel |first8=H.G. |last9=Montañez |first9=I.P. |date=2015-08-01 |df=dmy-all |title=The evolution of the global selenium cycle: Secular trends in Se isotopes and abundances |journal=Geochimica et Cosmochimica Acta |volume=162 |pages=109–125 |doi=10.1016/j.gca.2015.04.033 |issn=0016-7037 |bibcode=2015GeCoA.162..109S|doi-access=free }}</ref>

== Hypotheses ==
There may have been a gap of up to 900&nbsp;million years between the start of photosynthetic oxygen production and the geologically rapid increase in atmospheric oxygen about 2.5–2.4&nbsp;billion years ago. Several hypotheses propose to explain this time lag.

=== Increasing flux ===
Some people suggest that GOE is caused by the increase of the source of oxygen. One hypothesis argues that GOE was the immediate result of photosynthesis, although the majority of scientists suggest that a long-term increase of oxygen is more likely the case.<ref>{{Cite journal |last1=Kirschvink |first1=Joseph L. |last2=Kopp |first2=Robert E. |date=2008-08-27 |title=Palaeoproterozoic ice houses and the evolution of oxygen-mediating enzymes: the case for a late origin of photosystem&nbsp;II |journal=Philosophical Transactions of the Royal Society&nbsp;B: Biological Sciences |volume=363 |issue=1504 |pages=2755–2765 |doi=10.1098/rstb.2008.0024 |pmid=18487128 |pmc=2606766 |issn=0962-8436}}</ref> Several model results show possibilities of long-term increase of carbon burial,<ref>{{Cite journal |last1=des Marais |first1=David J. |last2=Strauss |first2=Harald |last3=Summons |first3=Roger E. |last4=Hayes |first4=J.M. |date=October 1992 |title=Carbon isotope evidence for the stepwise oxidation of the Proterozoic environment |journal=Nature |volume=359 |issue=6396 |pages=605–609 |doi=10.1038/359605a0 |pmid=11536507|issn=0028-0836 |bibcode=1992Natur.359..605M}}</ref> but the conclusions are indecisive.<ref>{{Cite journal|last1=Krissansen-Totton |first1=J. |last2=Buick |first2=R. |last3=Catling|first3=D.C. |date=2015-04-01 |title=A statistical analysis of the carbon isotope record from the Archean to Phanerozoic and implications for the rise of oxygen |journal=American Journal of Science |volume=315 |issue=4 |pages=275–316 |doi=10.2475/04.2015.01 |issn=0002-9599 |bibcode=2015AmJS..315..275K}}</ref>

=== Decreasing sink ===
In contrast to the increasing flux hypothesis, there are also several hypotheses that attempt to use decrease of sinks to explain GOE. One theory suggests that composition of the volatiles from volcanic gases was more oxidized.<ref name=":0">{{cite journal |last=Holland |first=Heinrich D. |date=November 2002 |title=Volcanic gases, black smokers, and the great oxidation event |journal=Geochimica et Cosmochimica Acta |volume=66 |issue=21 |pages=3811–3826 |doi=10.1016/s0016-7037(02)00950-x |issn=0016-7037 |bibcode=2002GeCoA..66.3811H}}</ref> Another theory suggests that the decrease of metamorphic gases and [[Serpentinite|serpentinization]] is the main key of GOE. Hydrogen and methane released from metamorphic processes are also lost from Earth's atmosphere over time and leave the crust oxidized.<ref name="Catling 839–843">{{Cite journal |last=Catling |first=D.C. |date=2001-08-03 |title=Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth |journal=Science |volume=293 |issue=5531 |pages=839–843 |doi=10.1126/science.1061976 |pmid=11486082 |bibcode=2001Sci...293..839C}}</ref> Scientists realized that hydrogen would escape into space through a process called methane photolysis, in which methane decomposes under the action of ultraviolet light in the upper atmosphere and releases its hydrogen. The escape of hydrogen from the Earth into space must have oxidized the Earth because the process of hydrogen loss is chemical oxidation.<ref name="Catling 839–843"/>

===Tectonic trigger===
[[File:Black-band ironstone (aka).jpg|thumb|right|2.1-billion-year-old rock showing banded iron formation]]
One hypothesis suggests that the oxygen increase had to await tectonically driven changes in the Earth, including the appearance of shelf seas, where reduced organic carbon could reach the sediments and be buried.<ref>{{cite journal |first1=T.M. |last1=Lenton |first2=H.J. |last2=Schellnhuber |first3=E. |last3=Szathmáry |date=2004 |title=Climbing the co-evolution ladder |journal=[[Nature (journal)|Nature]] |volume=431 |pmid=15496901 |issue=7011 |pages=913 |doi=10.1038/431913a |bibcode=2004Natur.431..913L}}</ref><ref>{{cite journal |last1=Eguchi |first1=James |last2=Seales |first2=Johnny |last3=Dasgupta |first3=Rajdeep |date=2019 |title=Great Oxidation and Lomagundi events linked by deep cycling and enhanced degassing of carbon |url=https://www.nature.com/articles/s41561-019-0492-6.epdf |journal=Nature Geoscience |doi=10.1038/s41561-019-0492-6 |access-date=2019-12-13 |df=dmy-all |volume=13 |issue=1 |pages=71–76|pmid=31807138 |pmc=6894402 |bibcode=2019NatGe..13...71E }}</ref> The newly produced oxygen was first consumed in various chemical reactions in the oceans, primarily with [[iron]]. Evidence is found in older rocks that contain massive [[banded iron formation]]s apparently laid down as this iron and oxygen first combined; most present-day [[iron ore]] lies in these deposits. It was assumed oxygen released from cyanobacteria resulted in the chemical reactions that created rust, but it appears the iron formations were caused by anoxygenic phototrophic iron-oxidizing bacteria, which does not require oxygen.<ref>{{cite news |url=https://phys.org/news/2013-04-iron-primeval-seas-rusted-bacteria.html |date=Apr 2013 |title=Iron in primeval seas rusted by bacteria |website=Phys.org}}</ref> Evidence suggests oxygen levels spiked each time smaller land masses collided to form a super-continent. Tectonic pressure thrust up mountain chains, which eroded to release nutrients into the ocean to feed photosynthetic cyanobacteria.<ref>{{cite web |url=http://www.scientificamerican.com/podcast/episode/5C271294-EE45-D925-BEBBEF03016A7CF4/ |title=Abundant Oxygen Indirectly Due to Tectonics |last=American |first=Scientific |website=Scientific American |access-date=2016-04-06 |archive-date=28 August 2018 |archive-url=https://web.archive.org/web/20180828091558/https://www.scientificamerican.com/podcast/episode/5C271294-EE45-D925-BEBBEF03016A7CF4/ }}</ref>

===Nickel famine===
Early [[Chemosynthesis|chemosynthetic organisms]] likely produced [[methane]], an important trap for molecular oxygen, since methane readily [[Oxidation|oxidizes]] to [[carbon dioxide]] (CO<sub>2</sub>) and water in the presence of [[Ultraviolet|UV radiation]]. Modern [[methanogens]] require [[nickel]] as an [[Cofactor (biochemistry)|enzyme cofactor]]. As the Earth's crust cooled and the supply of volcanic nickel dwindled, oxygen-producing algae began to out-perform methane producers, and the oxygen percentage of the atmosphere steadily increased.<ref>{{cite web |url=http://www.scientificamerican.com/podcast/episode/breathing-easy-thanks-to-great-oxid-09-04-13/ |title=Breathing Easy Thanks to the Great Oxidation Event |publisher=Scientific American |access-date=2016-04-06 |df=dmy-all}}</ref> From 2.7 to 2.4&nbsp;billion years ago, the rate of deposition of nickel declined steadily from a level 400&nbsp;times today's.<ref>{{cite journal |author1=Konhauser, Kurt O. |display-authors=etal |title=Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event |journal=Nature|volume=458 |issue=7239 |pages=750–753 |year=2009 |pmid=19360085 |doi=10.1038/nature07858 |bibcode=2009Natur.458..750K}}</ref>

===Bistability===
Another hypothesis posits a model of the atmosphere that exhibits [[bistability]]: two [[steady state]]s of oxygen concentration. The state of stable low oxygen concentration (0.02%) experiences a high rate of methane oxidation. If some event raises oxygen levels beyond a moderate threshold, the formation of an [[ozone layer]] shields UV rays and decreases methane oxidation, raising oxygen further to a stable state of 21% or more. The Great Oxygenation Event can then be understood as a [[phase transition|transition]] from the lower to the upper steady states.<ref>{{Cite journal |author1=Goldblatt, C. |author2=Lenton, T.M. |author3=Watson, A.J. |date=2006 |title=The Great Oxidation at 2.4&nbsp;Ga as a bistability in atmospheric oxygen due to UV shielding by ozone |journal=Geophysical Research Abstracts |volume=8 |page=00770 |url=http://www.cosis.net/abstracts/EGU06/00770/EGU06-J-00770.pdf}}</ref><ref>{{Cite journal |last1=Claire |first1=M.W. |last2=Catling |first2=D.C. |last3=Zahnle |first3=K.J. |date=December 2006 |title=Biogeochemical modelling of the rise in atmospheric oxygen |journal=Geobiology |volume=4 |issue=4 |pages=239–269 |doi=10.1111/j.1472-4669.2006.00084.x |issn=1472-4677}}</ref>

==Role in mineral diversification==
{{Main|Mineral evolution}}
The Great Oxygenation Event triggered an explosive growth in the diversity of [[mineral]]s, with many elements occurring in one or more oxidized forms near the Earth's surface.<ref>{{Cite journal|last1=Sverjensky|first1=Dimitri A. |last2=Lee |first2=Namhey |date=2010-02-01 |df=dmy-all |title=The Great Oxidation Event and Mineral Diversification |journal=Elements |volume=6 |issue=1 |pages=31–36 |doi=10.2113/gselements.6.1.31 |issn=1811-5209}}</ref> It is estimated that the GOE was directly responsible for more than 2,500 of the total of about 4,500&nbsp;minerals found on Earth today. Most of these new minerals were formed as [[hydrated]] and [[oxidized]] forms due to dynamic [[Mantle (geology)|mantle]] and [[Crust (geology)|crust]] processes.<ref name="sciam1">{{cite magazine |url=http://www.scientificamerican.com/article.cfm?id=evolution-of-minerals |title=Evolution of Minerals |magazine=Scientific American |date=March 2010}}</ref> 
{{Simple Horizontal timeline

|caption=Million years ago. [[Age of Earth]] = 4,560
|collapsible=yes
|row1=note
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|row1-1-text=Great Oxygenation
|row1-2-at=-2100
|row1-2-text=End of Huronian glaciation

|row2=timeline
|row2-1-to=-635
|row2-2-to=0
|row2-2-text={{Geological periods|-635|height=2.5em}}
|row3={{Geological eons|-2500|height=2.5em}}

|row4=scale

|from=-2500
|to=0
|axis-nudge=-1em
|inc=200

}}

== Role in cyanobacteria evolution ==
In a field research done in Lake Fryxell, Antarctica, researchers found out that mats of oxygen-producing cyanobacteria can produce a thin layer, one to two&nbsp;millimeters thick, of oxygenated water in an otherwise anoxic environment even under thick ice. Thus, before oxygen started accumulating in the atmosphere, these organisms could have possibly adapted to oxygen.<ref>{{cite news |website=ScienceDaily.com |url=https://www.sciencedaily.com/releases/2015/09/150901140759.htm |date=Sep 2015 |title=Oxygen oasis in Antarctic lake reflects Earth in distant past}}</ref><ref>{{cite journal |last1=Doran |first1=Peter T. |last2=Jungblut |first2=Anne D. |last3=Mackey |first3=Tyler J. |last4=Hawes |first4=Ian |last5=Sumner |first5=Dawn Y. |date=2015-10-01 |df=dmy-all |title=Antarctic microbial mats: A modern analog for Archean lacustrine oxygen oases |journal=Geology |volume=43 |issue=10 |pages=887–890 |doi=10.1130/G36966.1 |issn=0091-7613 |bibcode=2015Geo....43..887S |url=https://escholarship.org/uc/item/9gr788vv}}</ref> Eventually, the evolution of aerobic organisms that consumed oxygen established an equilibrium in the availability of oxygen. Free oxygen has been an important constituent of the atmosphere ever since.

==Origin of eukaryotes==
It has been proposed that a local rise in oxygen levels due to [[cyanobacteria]]l photosynthesis in ancient microenvironments was highly toxic to the surrounding biota, and that this selective pressure drove the evolutionary transformation of an [[archaea]]l lineage into the first [[eukaryote]]s.<ref name="pmid20731852">{{cite journal |author1=Gross, J. |author2=Bhattacharya, D. |title=Uniting sex and eukaryote origins in an emerging oxygenic world |journal=Biol. Direct |volume=5|pages=53 |date=August 2010 |pmid=20731852 |pmc=2933680 |doi=10.1186/1745-6150-5-53}}</ref>  [[Oxidative stress]] involving production of [[reactive oxygen species]] (ROS) might have acted in synergy with other environmental stresses (such as [[ultraviolet]] radiation and/or [[desiccation]]) to drive selection in an early archaeal lineage towards eukaryosis.  This archaeal ancestor may already have had [[DNA repair]] mechanisms based on DNA pairing and [[homologous recombination|recombination]] and possibly some kind of cell fusion mechanism.<ref name="pmid29436502">{{cite journal |vauthors=Hörandl E, Speijer D |title=How oxygen gave rise to eukaryotic sex |journal=Proc. Biol. Sci. |volume=285 |issue=1872 |page=20172706 |date=February 2018 |pmid=29436502 |pmc=5829205 |doi=10.1098/rspb.2017.2706}}</ref><ref>{{cite book |author1=Bernstein, H. |author2=Bernstein, C. |article=Sexual communication in archaea, the precursor to meiosis |pages=103–117 |title=Biocommunication of Archaea |editor=Witzany, Guenther |year=2017 |publisher=Springer International Publishing |isbn=978-3-319-65535-2 |doi=10.1007/978-3-319-65536-9}}</ref> The detrimental effects of internal ROS (produced by [[endosymbiont]] proto-[[Mitochondrion|mitochondria]]) on the archaeal [[genome]] could have promoted the [[origin and function of meiosis|evolution of meiotic sex]] from these humble beginnings.<ref name="pmid29436502"/> Selective pressure for efficient DNA repair of oxidative DNA damages may have driven the evolution of eukaryotic sex involving such features as cell-cell fusions, cytoskeleton-mediated chromosome movements and emergence of the [[nuclear membrane]].<ref name="pmid20731852"/> Thus the evolution of eukaryotic sex and eukaryogenesis were likely inseparable processes that evolved in large part to facilitate DNA repair.<ref name="pmid20731852" /><ref>{{cite book |author1=Bernstein, Harris |author2=Bernstein, Carol |chapter=Chapter&nbsp;3 – Evolutionary origin and adaptive function of meiosis |title=Meiosis |publisher=Intech Publ |editor1=Bernstein, Carol |editor2=Bernstein, Harris |pages=41–75 |year=2013}}</ref>

==See also==
*[[Geological history of oxygen]] – Timeline of the development of free oxygen in the Earth's oceans and atmosphere
* {{annotated link|Medea hypothesis}}
* {{annotated link|Pasteur point}}
*[[Rare Earth hypothesis]] – Hypothesis that complex extraterrestrial life is an extremely rare phenomenon
* {{annotated link|Stromatolite}}

==References==
{{Reflist|25em}}

==External links==
* {{cite magazine |url=https://www.newscientist.com/article/mg20527461.100-first-breath-earths-billionyear-struggle-for-oxygen/ |title=First breath: Earth's billion-year struggle for oxygen |magazine=New Scientist |issue=2746 |date=5 February 2010 |first=Nick |last=Lane |access-date=6 July 2020 |archive-date=6 January 2011 |archive-url=https://web.archive.org/web/20110106141826/http://ptc-cam.blogspot.com/2010/02/first-breath-earths-billion-year.html |url-status=dead }}

{{Proterozoic Footer}}

[[Category:Paleoproterozoic]]
[[Category:Origin of life]]
[[Category:Oxygen]]
[[Category:Climate history]]
[[Category:Events in the geological history of Earth]]
[[Category:Extinction events]]
[[Category:Meteorological hypotheses]]
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<small>This page was moved from [[:en:Great Oxidation Event]]. Its edit history can be viewed at [[Great Oxidation Event/edithistory]]</small></noinclude>