Editing Archean (section)

==Environment==
[[File:NASA-EarlyEarth-PaleOrangeDot-20190802.jpg|thumb|250px|''The pale orange dot'', an artist's impression of the [[early Earth]] which is believed to have appeared orange through its [[haze|hazy]], [[methane]] rich, [[prebiotic atmosphere|prebiotic second atmosphere]]. Earth's atmosphere at this stage was somewhat comparable to today's [[atmosphere of Titan]].<ref>{{cite journal |last1=Trainer |first1=Melissa G. |last2=Pavlov |first2=Alexander A. |last3=DeWitt |first3=H. Langley |last4=Jimenez |first4=Jose L. |last5=McKay |first5=Christopher P. |last6=Toon |first6=Owen B. |last7=Tolbert |first7=Margaret A. |date=2006-11-28 |title=Organic haze on Titan and the early Earth |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |issn=0027-8424 |doi=10.1073/pnas.0608561103 |doi-access=free |pmid=17101962 |pmc=1838702 |volume=103 |issue=48 |pages=18035–18042}}</ref>]]

The Archean atmosphere is thought to have almost completely lacked [[Dioxygen_in_biological_reactions|free oxygen]]; oxygen levels were less than 0.001% of their present atmospheric level,<ref name=AnoxicArchaeanAtmosphere>{{cite journal |last1=Pavlov |first1=A. A. |last2=Kasting |first2=J. F. |date=5 Jul 2004 |title=Mass-Independent Fractionation of Sulfur Isotopes in Archean Sediments: Strong Evidence for an Anoxic Archean Atmosphere |journal=[[Astrobiology (journal)|Astrobiology]] |doi=10.1089/153110702753621321 |pmid=12449853 |volume=2 |issue=1 |pages=27–41 |bibcode=2002AsBio...2...27P |url=https://www.liebertpub.com/doi/abs/10.1089/153110702753621321 |access-date=12 November 2022}}</ref><ref>{{cite journal |last1=Zhang |first1=Shuichang |last2=Wang |first2=Xiaomei |last3=Wang |first3=Huajian |last4=Bjerrum |first4=Christian J. |last5=Hammarlund |first5=Emma U. |last6=Costa |first6=M. Mafalda |last7=Connelly |first7=James N. |last8=Zhang |first8=Baomin |last9=Su |first9=Jin |last10=Canfield |first10=Donald Eugene |date=4 January 2016 |title=Sufficient oxygen for animal respiration 1,400 million years ago |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |doi=10.1073/pnas.1523449113 |doi-access=free |pmid=26729865 |pmc=4763753 |bibcode=2016PNAS..113.1731Z |volume=113 |issue=7 |pages=1731–1736}}</ref> with some analyses suggesting they were as low as 0.00001% of modern levels.<ref name=AtmosphericOxygenTheory>{{cite journal |last1=Laakso |first1=T. A. |last2=Schrag |first2=D. P. |date=5 April 2017 |title=A theory of atmospheric oxygen |journal=[[Geobiology (journal)|Geobiology]] |doi=10.1111/gbi.12230 |pmid=28378894 |s2cid=22594748 |volume=15 |issue=3 |pages=366–384 |bibcode=2017Gbio...15..366L |url=https://pubmed.ncbi.nlm.nih.gov/28378894/ |access-date=12 November 2022}}</ref> However, transient episodes of heightened oxygen concentrations are known from this eon around 2,980–2,960 Ma,<ref name=Oxygen3Ga>{{cite journal |last1=Crowe |first1=Sean A. |last2=Døssing |first2=Lasse N. |last3=Beukes |first3=Nicolas J. |last4=Bau |first4=Michael |last5=Kruger |first5=Stephanus J. |last6=Frei |first6=Robert |last7=Canfield |first7=Donald Eugene |date=25 September 2013 |title=Atmospheric oxygenation three billion years ago |journal=[[Nature (journal)|Nature]] |doi=10.1038/nature12426 |pmid=24067713 |s2cid=4464710 |volume=501 |issue=7468 |pages=535–538 |bibcode=2013Natur.501..535C |url=https://www.nature.com/articles/nature12426#citeas |access-date=12 November 2022}}</ref> 2,700 Ma,<ref name=LargeEtAl2022>{{cite journal |last1=Large |first1=Ross R. |last2=Hazen |first2=Robert M. |last3=Morrison |first3=Shaunna M. |last4=Gregory |first4=Dan D. |last5=Steadman |first5=Jeffrey A. |last6=Mukherjee |first6=Indrani |date=May 2022 |title=Evidence that the GOE was a prolonged event with a peak around 1900 Ma |journal=Geosystems and Geoenvironment |doi=10.1016/j.geogeo.2022.100036 |s2cid=246755121 |volume=1 |issue=2 |page=100036 |bibcode=2022GsGe....100036L |doi-access=free }}</ref> and 2,501 Ma.<ref name=WhiffOfOxygen>{{cite journal |last1=Anbar |first1=Ariel D. |last2=Duan |first2=Yun |last3=Lyons |first3=Timothy W. |last4=Arnold |first4=Gail N. |last5=Kendall |first5=Brian |last6=Creaser |first6=Robert A. |last7=Kaufman |first7=Alan J. |last8=Gordon |first8=Gwyneth W. |last9=Scott |first9=Clinton |last10=Garvin |first10=Jessica |last11=Buick |first11=Roger |date=28 September 2007 |title=A Whiff of Oxygen Before the Great Oxidation Event? |journal=[[Science (journal)|Science]] |doi=10.1126/science.1140325 |pmid=17901330 |s2cid=25260892 |volume=317 |issue=5846 |pages=1903–1906 |bibcode=2007Sci...317.1903A |url=https://www.science.org/doi/10.1126/science.1140325 |access-date=12 November 2022}}</ref><ref name=ArchaeanOxidativeWeathering>{{cite journal |last1=Reinhard |first1=Christopher T. |last2=Raiswell |first2=Robert |last3=Scott |first3=Clinton |last4=Anbar |first4=Ariel D. |last5=Lyons |first5=Timothy W. |date=30 October 2009 |title=A Late Archean Sulfidic Sea Stimulated by Early Oxidative Weathering of the Continents |journal=[[Science (journal)|Science]] |volume=326 |issue=5953 |pages=713–716 |doi=10.1126/science.1176711 |pmid=19900929 |bibcode=2009Sci...326..713R |s2cid=25369788 |url=https://www.science.org/doi/10.1126/science.1176711 |access-date=12 November 2022}}</ref> The pulses of increased oxygenation at 2,700 and 2,501 Ma have both been considered by some as potential start points of the [[Great Oxygenation Event]],<ref name=LargeEtAl2022/><ref>{{cite journal |last1=Warke |first1=Matthew R. |last2=Di Rocco |first2=Tommaso |last3=Zerkle |first3=Aubrey L. |last4=Lepland |first4=Aivo |last5=Prave |first5=Anthony R. |last6=Martin |first6=Adam P. |last7=Ueno |first7=Yuichiro |last8=Condon |first8=Daniel J. |last9=Claire |first9=Mark W. |date=2020-06-16 |title=The Great Oxidation Event preceded a Paleoproterozoic "snowball Earth" |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |issn=0027-8424 |doi=10.1073/pnas.2003090117 |doi-access=free |pmc=7306805 |pmid=32482849 |volume=117 |issue=24 |pages=13314–13320|bibcode=2020PNAS..11713314W }}</ref> which most scholars consider to have begun in the [[Palaeoproterozoic]]  ({{circa|2.4 Ga}}).<ref>{{cite journal |last1=Luo |first1=Genming |last2=Ono |first2=Shuhei |last3=Beukes |first3=Nicolas J. |last4=Wang |first4=David T. |last5=Xie |first5=Shucheng |last6=Summons |first6=Roger E. |date=2016-05-06 |title=Rapid oxygenation of Earth's atmosphere 2.33 billion years ago |journal=[[Science Advances]] |issn=2375-2548 |doi=10.1126/sciadv.1600134 |pmc=4928975 |pmid=27386544 |volume=2 |issue=5 |pages=e1600134|bibcode=2016SciA....2E0134L }}</ref><ref>{{cite journal |last1=Poulton |first1=Simon W. |last2=Bekker |first2=Andrey |last3=Cumming |first3=Vivien M. |last4=Zerkle |first4=Aubrey L. |last5=Canfield |first5=Donald E. |last6=Johnston |first6=David T. |date=April 2021 |title=A 200-million-year delay in permanent atmospheric oxygenation |journal=Nature |issn=1476-4687 |doi=10.1038/s41586-021-03393-7 |pmid=33782617 |s2cid=232419035 |volume=592 |issue=7853 |pages=232–236 |bibcode=2021Natur.592..232P |url=https://www.nature.com/articles/s41586-021-03393-7 |access-date=7 January 2023|hdl=10023/24041 |hdl-access=free }}</ref><ref name=GumsleyEtAl2017PNAS>{{cite journal |last1=Gumsley |first1=Ashley P. |last2=Chamberlain |first2=Kevin R. |last3=Bleeker |first3=Wouter |last4=Söderlund |first4=Ulf |last5=De Kock |first5=Michiel O. |last6=Larsson |first6=Emilie R. |last7=Bekker |first7=Andrey |date=6 February 2017 |title=Timing and tempo of the Great Oxidation Event |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |issn=0027-8424 |doi=10.1073/pnas.1608824114 |doi-access=free |pmc=5338422 |pmid=28167763 |volume=114 |issue=8 |pages=1811–1816|bibcode=2017PNAS..114.1811G }}</ref> Furthermore, oases of relatively high oxygen levels existed in some nearshore shallow marine settings by the Mesoarchean.<ref>{{cite journal |last1=Eickmann |first1=Benjamin |last2=Hofmann |first2=Axel |last3=Wille |first3=Martin |last4=Bui |first4=Thi Hao |last5=Wing |first5=Boswell A. |last6=Schoenberg |first6=Ronny |date=15 January 2018 |title=Isotopic evidence for oxygenated Mesoarchaean shallow oceans |journal=[[Nature Geoscience]] |doi=10.1038/s41561-017-0036-x |s2cid=135023426 |volume=11 |issue=2 |pages=133–138 |bibcode=2018NatGe..11..133E |url=https://www.nature.com/articles/s41561-017-0036-x?error=cookies_not_supported&code=54e99c94-9890-439d-a813-c26d056ce863 |access-date=25 December 2022}}</ref> The ocean was broadly [[reducing agent|reducing]] and lacked any persistent [[redoxcline]], a water layer between oxygenated and anoxic layers with a strong [[reduction–oxidation|redox]] gradient, which would become a feature in later, more oxic oceans.<ref>{{cite journal |last1=Zhou |first1=Hang |last2=Zhou |first2=Wenxiao |last3=Wei |first3=Yunxu |last4=Chi Fru |first4=Ernest |last5=Huang |first5=Bo |last6=Fu |first6=Dong |last7=Li |first7=Haiquan |last8=Tan |first8=Mantang |date=December 2022 |title=Mesoarchean banded iron-formation from the northern Yangtze Craton, South China and its geological and paleoenvironmental implications |journal=[[Precambrian Research]] |doi=10.1016/j.precamres.2022.106905 |volume=383 |page=106905 |bibcode=2022PreR..38306905Z |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926822003497 |access-date=17 December 2022}}</ref> Despite the lack of free oxygen, the rate of organic carbon burial appears to have been roughly the same as in the present.<ref>{{cite journal |last1=Fischer |first1=W. W. |last2=Schroeder |first2=S. |last3=Lacassie |first3=J. P. |last4=Beukes |first4=N. J. |last5=Goldberg |first5=T. |last6=Strauss |first6=H. |last7=Horstmann |first7=U. E. |last8=Schrag |first8=D. P. |last9=Knoll |first9=A. H. |date=March 2009 |title=Isotopic constraints on the Late Archean carbon cycle from the Transvaal Supergroup along the western margin of the Kaapvaal Craton, South Africa |journal=[[Precambrian Research]] |doi=10.1016/j.precamres.2008.10.010 |volume=169 |issue=1–4 |pages=15–27 |bibcode=2009PreR..169...15F |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926808002490 |access-date=24 November 2022}}</ref> Due to extremely low oxygen levels, sulphate was rare in the Archean ocean, and sulphides were produced primarily through reduction of organically sourced sulphite or through mineralisation of compounds containing reduced sulphur.<ref>{{cite journal |last1=Fakhraee |first1=Mojtaba |last2=Katsev |first2=Sergei |date=7 October 2019 |title=Organic sulfur was integral to the Archean sulfur cycle |journal=[[Nature Communications]] |doi=10.1038/s41467-019-12396-y |pmid=31591394 |pmc=6779745 |volume=10 |issue=1 |page=4556|bibcode=2019NatCo..10.4556F }}</ref> The Archean ocean was enriched in heavier oxygen isotopes relative to the modern ocean, though [[δ18O]] values decreased to levels comparable to those of modern oceans over the course of the later part of the eon as a result of increased continental weathering.<ref>{{cite journal |last1=Johnson |first1=Benjamin W. |last2=Wing |first2=Boswell A. |date=2 March 2020 |title=Limited Archaean continental emergence reflected in an early Archaean 18O-enriched ocean |journal=[[Nature Geoscience]] |doi=10.1038/s41561-020-0538-9 |s2cid=211730235 |volume=13 |issue=3 |pages=243–248 |bibcode=2020NatGe..13..243J |url=https://www.nature.com/articles/s41561-020-0538-9?error=cookies_not_supported&code=bee768fe-63d9-40f0-9508-cddc3686d03a |access-date=7 January 2023}}</ref>

Astronomers think that the Sun had about 75–80&nbsp;percent of its present luminosity,<ref name=DauphasKasting2011>{{cite journal |last1=Dauphas |first1=Nicolas |last2=Kasting |first2=James Fraser |date=1 June 2011 |title=Low pCO2 in the pore water, not in the Archean air |journal=Nature |doi=10.1038/nature09960 |pmid=21637211 |s2cid=205224575 |volume=474 |issue=7349 |pages=E2-3; discussion E4-5 |bibcode=2011Natur.474E...1D |doi-access=free }}</ref> yet temperatures on Earth appear to have been near modern levels only 500&nbsp;million years after Earth's formation (the [[faint young Sun paradox]]). The presence of liquid water is evidenced by certain highly deformed [[gneiss]]es produced by metamorphism of [[sediment]]ary [[protolith]]s. The moderate temperatures may reflect the presence of greater amounts of greenhouse gases than later in the Earth's history.<ref name=Walker1982>{{cite journal |last1=Walker |first1=James C. G. |date=November 1982 |title=Climatic factors on the Archean earth |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |doi=10.1016/0031-0182(82)90082-7 |hdl=2027.42/23810 |volume=40 |issue=1–3 |pages=1–11 |bibcode=1982PPP....40....1W |url=https://www.sciencedirect.com/science/article/abs/pii/0031018282900827 |access-date=12 November 2022|hdl-access=free }}</ref><ref name=Walker1985>{{cite journal |last=Walker |first=James C.G. |date=June 1985 |title=Carbon dioxide on the early earth |journal=[[Origins of Life and Evolution of Biospheres]] |doi=10.1007/BF01809466 |bibcode=1985OrLi...16..117W |hdl=2027.42/43349 |hdl-access=free |pmid=11542014 |s2cid=206804461 |volume=16 |issue=2 |pages=117–127 |url=http://deepblue.lib.umich.edu/bitstream/2027.42/43349/1/11084_2005_Article_BF01809466.pdf |access-date=30 January 2010 |df=dmy-all}}</ref><ref name=Pavlov2000>{{cite journal |vauthors=Pavlov AA, Kasting JF, Brown LL, Rages KA, Freedman R |date=May 2000 |title=Greenhouse warming by CH<sub>4</sub> in the atmosphere of early Earth |journal=[[Journal of Geophysical Research]] |doi=10.1029/1999JE001134 |doi-access=free |bibcode=2000JGR...10511981P |pmid=11543544 |volume=105 |issue=E5 |pages=11981–11990}}</ref> Extensive abiotic denitrification took place on the Archean Earth, pumping the greenhouse gas [[nitrous oxide]] into the atmosphere.<ref>{{cite journal |last1=Buessecker |first1=Steffen |last2=Imanaka |first2=Hiroshi |last3=Ely |first3=Tucker |last4=Hu |first4=Renyu |last5=Romaniello |first5=Stephen J. |last6=Cadillo-Quiroz |first6=Hinsby |date=5 December 2022 |title=Mineral-catalysed formation of marine NO and N2O on the anoxic early Earth |url=https://www.nature.com/articles/s41561-022-01089-9 |journal=[[Nature Geoscience]] |volume=15 |issue=1 |pages=1056–1063 |doi=10.1038/s41561-022-01089-9 |bibcode=2022NatGe..15.1056B |s2cid=254276951 |access-date=28 April 2023}}</ref> Alternatively, Earth's [[albedo]] may have been lower at the time, due to less land area and cloud cover.<ref name=Rosing>{{cite journal |vauthors=Rosing MT, Bird DK, Sleep NH, Bjerrum CJ |date=April 2010 |title=No climate paradox under the faint early Sun |journal=[[Nature (journal)|Nature]] |pmid=20360739 |doi=10.1038/nature08955 |bibcode=2010Natur.464..744R |s2cid=205220182 |volume=464 |issue=7289 |pages=744–747}}</ref>