Editing Hadean (section)

==Oceans==
{{anchor|Cool early Earth}}
[[File:Precambrian - Zircon ages.png|thumb|upright=1.6|Hadean and Archean Zircons with evaluation of δ<sup>18</sup> O]]
Studies of zircons have found that liquid water may have existed between 4.0 and 4.4 billion years ago, very soon after the formation of Earth.<ref name=Wilde2001/><ref name=Valley2002>{{cite journal |last1=Valley |first1=John W. |last2=Peck |first2=William H. |last3=King |first3=Elizabeth M. |last4=Wilde |first4=Simon A. |date=April 2002 |title=A Cool Early Earth |journal=Geology |doi=10.1130/0091-7613(2002)030<0351:ACEE>2.0.CO;2 |pmid=16196254 |bibcode=2002Geo....30..351V |volume=30 |issue=4 |pages=351–354 |url=http://www.geology.wisc.edu/%7Evalley/zircons/cool_early/cool_early_home.html |access-date=2006-08-22 |url-status=dead |archive-url=https://web.archive.org/web/20130616213221/http://www.geology.wisc.edu/~valley/zircons/cool_early/cool_early_home.html |archive-date=2013-06-16}}</ref><ref>{{cite journal|last1=Cavosie|first1=AJ|last2=Valley|first2=JW|last3=Wilde|first3=SA|year=2005|url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X05002773|title=Magmatic d18O in 4400-3900 Ma detrital zircons: A record of the alteration and recycling of crust in the Early Archean|journal=Earth and Planetary Science Letters|volume=235|pages=663–681|doi=10.1016/j.epsl.2005.04.028 }}</ref><ref>{{cite journal|first1=EM|last1=Cameron|first2=TB|last2=Blum|last3=Cavosie|first3=AJ|display-authors=et al|year=2024|url=https://www.degruyter.com/document/doi/10.2138/am-2023-9180/html|title=Evidence for oceans pre-4300 Ma confirmed by preserved igneous compositions in Hadean zircon|journal=American Mineralogist|volume=109|issue=10|pages=1670–1681|doi=10.2138/am-2023-9180|bibcode=2024AmMin.109.1670C |doi-access=free}}</ref> Liquid water oceans existed despite the high surface temperature, because at an atmospheric pressure of 27 atmospheres, water remains liquid even at those high temperatures.<ref name=Sleep2001/>

The most likely source of the water in the Hadean ocean was outgassing from the [[Earth's mantle]].<ref>{{cite encyclopedia|title=Encyclopedia of Geology|isbn=9780081029091|year=2020|publisher=Elsevier Science|editor1-first=David|editor1-last=Alderton|editor2-first=Scott|editor2-last=Elias|entry=Precambrian|last1=Reis|first1=HLS|last2=Sanchez|first2=EAM|page=30}}</ref> [[Late Heavy Bombardment|Bombardment]] origin of a substantial amount of water is unlikely, due to the incompatibility of [[isotope]] fractions between the Earth and comets.<ref name=Drake/>

Asteroid impacts during the Hadean and into the Archean would have periodically disrupted the ocean. The geological record from 3.2 Gya contains evidence of multiple impacts of objects up to {{convert|100|km}} in diameter.<ref name=Lowe2015>{{cite journal |last1=Lowe |first1=DR |last2=Byerly |first2=GR |year=2015 |title=Geologic record of partial ocean evaporation triggered by giant asteroid impacts, 3.29–3.23 billion years ago |journal=Geology |doi=10.1130/G36665.1 |bibcode=2015Geo....43..535L |volume=43 |issue=6 |pages=535–538}}</ref> Each such impact would have boiled off up to {{convert|100|m}} of a global ocean, and temporarily raised the atmospheric temperature to {{convert|500|C|F}}.<ref name=Lowe2015/> However, the frequency of meteorite impacts is still under study: the Earth may have gone through long periods when liquid oceans and life were possible.<ref name=Valley2002/>

The liquid water would absorb the carbon dioxide in the early atmosphere; this would not be enough by itself to substantially reduce the amount of {{chem|CO|2}}.<ref name=Sleep2001/>