Editing Hadean

{{Short description|Geologic eon, 4567–4031 million years ago}}
{{for|the Romanian chef|Adrian Hădean}}
{{Infobox geologic timespan
| name                      = {{Color|White|Hadean}}
| color                     = Hadean
| top_bar                   = all time
| time_start                = {{Period start|hadean}}
| time_start_uncertainty    = 0.16
| time_end                  = 4031
| time_end_uncertainty      = 3
| image_outcrop             =
| caption_outcrop           =
| timeline                  = Eons
| former_subdivisions       =
| formerly_part_of          =
| partially_contained_in    =
| partially_contains        =
<!--Etymology-->
| chrono_name               =
| strat_name                =
| name_formality            =
| name_accept_date          =
| alternate_spellings       =
| synonym1                  = Priscoan Period
| synonym1_coined           = [[W. Brian Harland|Harland]] ''et al.'', 1989
| synonym2                  =
| synonym2_coined           =
| synonym3                  =
| synonym3_coined           =
| former_names              =
| proposed_names            =
<!--Usage Information-->
| celestial_body            = earth
| usage                     = Global ([[International Commission on Stratigraphy|ICS]])
<!--Definition-->
| chrono_unit               = Eon
| strat_unit                = Eonothem
| proposed_by               = [[Preston Cloud]], 1972
| timespan_formality        = Formal
| lower_boundary_def        = Age of  the oldest solid material in the [[Solar System]]'s [[protoplanetary disk]] (4567.30 ± 0.16) [[Megaannus|Ma]]<ref name="Episodes2024">{{cite journal | title=Ratification of the base of the ICS Geological Time Scale: the Global Standard Stratigraphic Age (GSSA) for the Hadean lower boundary | last1=Halla | first1=J. | display-authors=etal | journal=[[Episodes (journal)|Episodes]] | year=2024 | volume=47 | issue=2 | pages=381–389 | doi=10.18814/epiiugs/2024/024002| doi-access=free | hdl=2164/23819 | hdl-access=free }}</ref>
| lower_gssa_accept_date    = October 5th, 2022<ref name=Cohen2022>{{cite web |last=Cohen |first=Kim |date=October 2022 |title=New edition of the Chart - 2022-10 |website=International Commission on Stratigraphy |url=https://stratigraphy.org/news/143 |access-date=16 January 2023 |quote=2022/10 - Hadean: GSSA instated as ratified by IUGS (5-10-2022). The GSSA is 4,567.30 ± 0.16 Ma.}}</ref>
| upper_boundary_def           = Ten oldest U-Pb zircon ages
| upper_gssa_location          = Along the Acasta River, [[Northwest Territories]], [[Canada]]
| upper_gssa_coords            = {{Coord|65.1738|N|115.5538|W|display=inline}}
| upper_gssa_accept_date       = 2023<ref name="GSSP Web">{{cite web |title=Global Boundary Stratotype Section and Point |url=https://stratigraphy.org/gssps/ |publisher=International Commission of Stratigraphy |access-date=29 October 2023}}</ref>
}}

The '''Hadean''' ({{IPAc-en|h|eɪ|ˈ|d|iː|ə|n|,_|ˈ|h|eɪ|d|i|ə|n}} {{respell|hay|DEE|ən|,_|HAY|dee|ən}}) is the first and oldest of the four [[eon (geology)|geologic eon]]s of [[Earth]]'s [[history of Earth|history]], starting with [[formation of the Earth|the planet's formation]] about 4.6&nbsp;[[billion years ago]]<ref>{{cite journal |last=Dalrymple |first=G. Brent |year=2001 |title=The age of the Earth in the twentieth century: a problem (mostly) solved |journal=Geological Society, London, Special Publications |bibcode=2001GSLSP.190..205D |s2cid=130092094 |doi=10.1144/gsl.sp.2001.190.01.14 |volume=190 |issue=1 |pages=205–221 |url=https://www.lyellcollection.org/doi/10.1144/GSL.SP.2001.190.01.14 |access-date=2022-10-02}}</ref><ref>{{cite web |date=1997 |title=Age of the Earth |publisher=U.S. Geological Survey |url=http://pubs.usgs.gov/gip/geotime/age.html |access-date=2022-10-03 |url-status=live |archive-url=https://web.archive.org/web/20051223072700/http://pubs.usgs.gov/gip/geotime/age.html |archive-date= 23 December 2005}}</ref> (estimated 4567.30 ± 0.16 [[million years ago]]<ref name=Cohen2022/> set by the age of the oldest solid material in the [[Solar System]]—[[protoplanetary disk]] dust particles—found as [[chondrule]]s and [[calcium–aluminium-rich inclusion]]s in some [[meteorite]]s about 4.567&nbsp;billion years old),<ref name=GeolTimeScale2020>{{cite book |last1=Strachan |first1=R. |last2=Murphy |first2=J.B. |last3=Darling |first3=J. |last4=Storey |first4=C. |last5=Shields |first5=G. |chapter=Precambrian (4.56–1 Ga) |editor1-last=Gradstein |editor1-first=F.M. |editor2-last=Ogg |editor2-first=J.G. |editor3-last=Schmitz |editor3-first=M.D. |editor4-last=Ogg |editor4-first=G.M. |date=2020 |title=Geologic Time Scale 2020 |publisher=Elsevier |location=Amsterdam |isbn=978-0-12-824360-2 |doi=10.1016/B978-0-12-824360-2.00016-4 |s2cid=229513433 |pages=482–483}}</ref><ref name="Episodes2024" /> and ended 4.031&nbsp;billion years ago,  the age of the oldest known intact rock formations on Earth as recognized by the [[International Commission on Stratigraphy]].<ref>{{cite web |title=Global Boundary Stratotype Section and Point |url=https://stratigraphy.org/gssps/ |publisher=International Commission of Stratigraphy |access-date=21 April 2023}}</ref> The [[giant-impact hypothesis|interplanetary collision]] that created the [[Moon]] occurred early in this eon. The Hadean eon was succeeded by the [[Archean]] eon, with the [[Late Heavy Bombardment]] hypothesized to have occurred at the Hadean-Archean boundary.

Hadean rocks are very rare, largely consisting of [[Hadean zircon|granular zircon]]s from one locality ([[Jack Hills]]) in [[Western Australia]].<ref name=Korenaga2021>{{cite journal |last=Korenaga |first=J |year=2021 |title=Was There Land on the Early Earth? |journal=Life |doi=10.3390/life11111142 |doi-access=free |pmid=34833018 |pmc=8623345 |volume=11 |issue=11 |page=1142|bibcode=2021Life...11.1142K }}</ref> Hadean [[geophysical]] models remain controversial among [[geologist]]s: [[plate tectonics]] and the growth of [[craton]]s into [[continent]]s may have started in the Hadean, but there is still uncertainty.<ref name=Dhuime2012/><ref name=Harrison2009/><ref name=Windley2021/>

Earth in the early Hadean had a very thick [[hydride]]-rich [[Earth's atmosphere|atmosphere]] whose [[atmospheric chemistry|composition]] likely resembled the [[solar nebula]] and the [[gas giant]]s, with mostly [[water vapor]], [[methane]] and [[ammonia]]. As the Earth's surface cooled, vaporized atmospheric water [[condensation|condense]]d into [[liquid water]] and eventually a [[superocean]] covering nearly all of the planet was formed, turning Earth into an [[ocean planet]]. [[Volcanism|Volcanic]] [[outgassing]] and [[asteroid]] [[impact event|bombardment]]s further altered the Hadean atmosphere eventually into the [[nitrogen]]- and [[carbon dioxide]]-rich, [[reducing atmosphere|weakly reducing]] [[prebiotic atmosphere|Paleoarchean atmosphere]].

==Etymology==
The eon's name "Hadean" comes from [[Hades]], the [[Greek god]] of the [[Greek underworld|underworld]] (whose name is also used to describe the underworld itself), referring to the [[hell]]ish conditions then prevailing on [[early Earth]]: the planet had just been formed from recent [[accretion (astrophysics)|accretion]], and its surface was still molten with superheated [[lava]] due to that, the abundance of short-lived radioactive elements, and frequent [[impact event]]s with other Solar System bodies.

The term was coined by American geologist [[Preston Cloud]], originally to label the period before the earliest known [[rock (geology)|rock]]s on Earth.<ref>{{cite journal |last=Cloud |first=Preston |year=1972 |title=A working model of the primitive Earth |journal=American Journal of Science |volume=272 |issue=6 |pages=537–548 |bibcode=1972AmJS..272..537C |doi=10.2475/ajs.272.6.537}}</ref><ref>{{cite book |last=Bleeker |first=W. |year=2004 |chapter=Chapter&nbsp;10. Toward a 'natural' Precambrian time scale |editor1-last=Gradstein |editor1-first=Felix M. |editor2-last=Ogg |editor2-first=James G. |editor3-last=Smith |editor3-first=Alan G. |title=A Geologic Time Scale |publisher=Cambridge University Press |location=Cambridge, UK |isbn=9780521786737 |page=145 |chapter-url=https://books.google.com/books?id=rse4v1P-f9kC&pg=PA145}}</ref> [[W. Brian Harland|W.B. Harland]] later coined an almost synonymous term, the '''Priscoan period''', from ''priscus'', a Latin word for 'ancient'.<ref>{{cite encyclopedia |title=Priscoan |dictionary=Oxford Living dictionaries |url=https://en.oxforddictionaries.com/definition/priscoan |url-status=dead |archive-url=https://web.archive.org/web/20181129225130/https://en.oxforddictionaries.com/definition/priscoan |archive-date=2018-11-29}}</ref> Other, older texts refer to the eon as the '''Pre-Archean'''.<ref>{{cite conference |last=Shaw |first=D.M. |year=1975 |title=Early history of the Earth |conference=Proceedings of the NATO Advanced Study Institute |publisher=John Wiley |location=Leicester |isbn=0-471-01488-5 |pages=33–53}}</ref><ref>{{cite journal |last1=Jarvis |first1=Gary T. |last2=Campbell |first2=Ian H. |date=December 1983 |title=Archean komatiites and geotherms: Solution to an apparent contradiction |journal=Geophysical Research Letters |doi=10.1029/GL010i012p01133 |bibcode=1983GeoRL..10.1133J |volume=10 |issue=12 |pages=1133–1136}}</ref>

==Rock dating==
{{further|Oldest dated rocks}}

Prior to the 1980s and the discovery of [[Oldest dated rocks|Hadean lithic fragments]], scientific narratives of the early Earth explanations were almost entirely in the hands of [[Geodynamics|geodynamic]] modelers.<ref>{{cite book |last1=Harrison |first1=T. Mark |title=Hadean earth |date=2020 |publisher=Springer |location=Cham |isbn=978-3030466862 |page=4}}</ref>

[[File:Jack Hills detrital zircons BSE micrographs.jpg|thumb|left|Backscatter electron micrograph of detrital zircons from the Hadean (4.404 ± 0.008 Ga) [[metasediment]]s of the [[Jack Hills]], [[Narryer Gneiss terrane]], [[Western Australia]]]]

In the last decades of the 20th century, geologists identified a few Hadean rocks from western [[Greenland]], northwestern [[Canada]], and [[Western Australia]]. In 2015, traces of carbon minerals interpreted as "remains of [[Biotic material|biotic life]]" were found in 4.1-billion-year-old rocks in Western Australia.<ref>{{cite news |agency=[[Associated Press]] |last=Borenstein |first=Seth |date=19 October 2015 |title=Hints of life on what was thought to be desolate early Earth |work=[[Excite (web portal)|Excite]] |publisher=[[Mindspark Interactive Network]] |location=Yonkers, NY |url=http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html |access-date=2015-10-20}}</ref><ref>{{cite journal |last1=Bell |first1=Elizabeth A. |last2=Boehnike |first2=Patrick |last3=Harrison |first3=T. Mark |last4=Mao |first4=Wendy L. |display-authors=3 |date=19 October 2015 |title=Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon |journal=Proc. Natl. Acad. Sci. U.S.A. |issn=1091-6490 |publisher=[[National Academy of Sciences]] |location=Washington, D.C. |doi=10.1073/pnas.1517557112 |doi-access=free |pmid=26483481 |pmc=4664351 |bibcode=2015PNAS..11214518B |volume=112 |issue=47 |pages=14518–21}}</ref>

The oldest dated [[zircon]] crystals, enclosed in a [[Metamorphism|metamorphosed]] [[sandstone]] [[Conglomerate (geology)|conglomerate]] in the [[Jack Hills]] of the [[Narryer Gneiss terrane]] of Western Australia, date to 4.404 ± 0.008 [[Giga-annum|Ga]].<ref name=Wilde2001>{{cite journal |last1=Wilde |first1=Simon A. |last2=Valley |first2=John W. |last3=Peck |first3=William H. |last4=Graham |first4=Colin M. |date=2001 |title=Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago |journal=Nature |pmid=11196637 |bibcode=2001Natur.409..175W |s2cid=4319774 |doi=10.1038/35051550 |volume=409 |issue=6817 |pages=175–178}}</ref> This zircon is a slight outlier, with the oldest consistently dated zircon falling closer to 4.35 Ga<ref name=Wilde2001/>—around 200 million years after the hypothesized time of [[History of Earth#Origin of life|Earth's formation]].

In many other areas, [[xenocryst]] (or relict) [[Hadean zircon]]s enclosed in older rocks indicate that younger rocks have formed on older [[terrane]]s and have incorporated some of the older material. One example occurs in the [[Guiana Shield|Guiana shield]] from the Iwokrama Formation of southern Guyana where zircon cores have been dated at 4.22 Ga.<ref>{{cite journal |last1=Nadeau |first1=Serge |last2=Chen |first2=Wei |last3=Reece |first3=Jimmy |last4=Lachhman |first4=Deokumar |last5=Ault |first5=Randy |last6=Faraco |first6=Maria |last7=Fraga |first7=Leda |last8=Reis |first8=Nelson |last9=Betiollo |first9=Leandro |date=2013-12-01 |title=Guyana: the Lost Hadean crust of South America? |journal=Brazilian Journal of Geology |doi=10.5327/Z2317-48892013000400002 |doi-access=free |volume=43 |issue=4 |pages=601–606|bibcode=2013BrJG...43..601N }}</ref>

==Atmosphere==
A sizable quantity of water would have been in the material that formed Earth.<ref name=Drake>{{cite journal |last=Drake |first=Michael J. |date=April 2005 |title=Origin of water in the terrestrial planets |journal=Meteoritics & Planetary Science |bibcode=2005M&PS...40..515J |doi=10.1111/j.1945-5100.2005.tb00960.x |doi-access=free |volume=40 |number=4 |pages=519–527}}</ref> Water molecules would have escaped Earth's gravity more easily when the planet was less massive during its formation. [[Photodissociation]] by short-wave [[ultraviolet]] in [[sunlight]] could [[water splitting|split]] [[surface water]] molecules into [[oxygen]] and [[hydrogen]], the former of which would readily react to form compounds in the then-[[reducing atmosphere]], while the latter (along with the similarly light [[helium]]) would be expected to continually leave the atmosphere (as it does to the present day) due to [[atmospheric escape]].

Part of the ancient planet is theorized to have been disrupted by the [[giant impact hypothesis|impact that created the Moon]], which should have caused the melting of one or two large regions of Earth. Earth's present composition suggests that there was not complete remelting as it is difficult to completely melt and mix huge rock masses.<ref>{{cite web |last=Taylor |first=G. Jeffrey |title=Origin of the Earth and Moon |website=Solar System Exploration |publisher=NASA |url=http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=446 |url-status=dead |archive-url=https://web.archive.org/web/20150308165917/http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=446 |archive-date=March 8, 2015}}</ref> However, a fair fraction of material should have been vaporized by this impact. The material would have condensed within 2,000 years.<ref name=Sleep2001>{{cite journal |last1=Sleep |first1=NH |last2=Zahnle |first2=K |last3=Neuhoff |first3=PS |year=2001 |title=Initiation of clement surface conditions on the earliest Earth |journal=[[Proceedings of the National Academy of Sciences|PNAS]] |doi=10.1073/pnas.071045698 |doi-access=free |pmid=11259665 |pmc=31109 |bibcode=2001PNAS...98.3666S |volume=98 |issue=7 |pages=3666–3672}}</ref> The initial [[magma ocean]] solidified within 5 million years,<ref>{{cite journal|first=LT|last=Elkins-Tanton|title=Linked magma ocean solidification and atmospheric growth for Earth and Mars|journal=Earth and Planetary Science Letters|volume=271|issue=1–4|year=2008|pages=181–191|doi=10.1016/j.epsl.2008.03.062|bibcode=2008E&PSL.271..181E }}</ref> leaving behind hot volatiles which probably resulted in a heavy {{chem|link=carbon dioxide|CO|2}} atmosphere with [[hydrogen]] and [[water vapor]]. The initial heavy atmosphere had a surface temperature of {{cvt|230|C|F}} and an [[atmospheric pressure]] of above 27 [[standard atmosphere (unit)|standard atmosphere]]s.<ref name=Sleep2001/>

==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/>

==Plate tectonics==
[[File:Hadean and Archean continents.gif|thumb|upright=1.75|Evolution of continental crust and ocean depths (from Korenaga, 2021)<ref name=Korenaga2021/>]]
A 2008 study of zircons found that Australian Hadean rock contains minerals pointing to the existence of [[plate tectonics]] as early as 4 billion years ago (approximately 600 million years after Earth's formation).<ref>{{cite news |last=Chang |first=Kenneth |date=December 2, 2008 |title=A New Picture of the Early Earth |work=[[The New York Times]] |url=https://www.nytimes.com/2008/12/02/science/02eart.html?_r=1}}</ref> However, some geologists suggest that the zircons could have been formed by meteorite impacts.<ref>{{cite journal |last1=Kenny |first1=GG |last2=Whitehouse |first2=MJ |last3=Kamber |first3=BS |display-authors=etal |date=April 12, 2016 |title=Differentiated impact melt sheets may be a potential source of Hadean detrital zircon |journal=Geology |volume=44 |issue=6 |pages=435–438 |doi=10.1130/G37898.1 |bibcode=2016Geo....44..435K |url=http://geology.geoscienceworld.org/content/44/6/435 |accessdate=March 6, 2017}}</ref> The direct evidence of Hadean geology from zircons is limited, because the zircons are largely gathered in one locality in Australia.<ref name=Korenaga2021/><ref name=Harrison2020/> Geophysical models are underconstrained, but can paint a general picture of the state of Earth in the Hadean.<ref name=Korenaga2021/><ref>{{cite journal |last1=Korenaga |first1=J |last2=Planavsky |first2=NJ |last3=Evans |first3=DAD |year=2017 |title=Global water cycle and the coevolution of Earth's interior and surface environment. |journal=Phil. Trans. R. Soc. A |doi=10.1098/rsta.2015.0393 |pmid=28416728 |pmc=5394256 |bibcode=2017RSPTA.37550393K |s2cid=2958757 |volume=375 |issue=2094 |page=20150393}}</ref>

[[Mantle convection]] in the Hadean was likely vigorous, due to lower [[viscosity]].<ref name=Korenaga2021/> The lower viscosity was due to the high levels of [[radiogenic heat]] and the fact that water in the mantle had not yet fully outgassed.<ref name=Korenaga2021a>{{cite journal |last=Korenaga |first=J |year=2021 |title=Hadean geodynamics and the nature of early continental crust |journal=Precambrian Res |doi=10.1016/j.precamres.2021.106178 |bibcode=2021PreR..35906178K |s2cid=233441822 |volume=359 |page=106178}}</ref> Whether the vigorous convection led to plate tectonics in the Hadean or was confined under a rigid lid is still a matter of debate.<ref name=Korenaga2021/><ref name=Windley2021>{{cite journal |last1=Windley |first1=BF |last2=Kusky |first2=T |last3=Polat |first3=A |year=2021 |title=Onset of plate tectonics by the Eoarchean |journal=Precambrian Res |doi=10.1016/j.precamres.2020.105980 |bibcode=2021PreR..35205980W |s2cid=228993361 |volume=352 |page=105980}}</ref><ref name=Harrison2020>{{cite book |last=Harrison |first=T. Mark |year=2020 |title=Hadean Earth |publisher=Springer |location=Cham, Switzerland |isbn=978-3-030-46686-2 |doi=10.1007/978-3-030-46687-9 |page=|bibcode=2020hade.book.....H |s2cid=128932829 }}</ref><ref name=Tang2016>{{cite journal |last1=Tang |first1=M |last2=Chen |first2=K |last3=Rudnick |first3=RL |year=2016 |title=Archean upper crust transition from mafic to felsic marks the onset of plate tectonics |journal=Science |doi=10.1126/science.aad5513 |pmid=26798012|bibcode=2016Sci...351..372T |s2cid=206643793 |volume=351 |issue=6271 |pages=372–375|doi-access=free }}</ref> The presence of Hadean oceans is thought to have triggered plate tectonics.<ref name=Regenauer2001>{{cite journal |last1=Regenauer-Lieb |first1=K |last2=Yuen |first2=DA |last3=Branlund |first3=J |year=2001 |title=The initiation of subduction: Criticality by addition of water? |journal=Science |doi=10.1126/science.1063891 |pmid=11641494 |bibcode=2001Sci...294..578R |s2cid=43547982 |volume=294 |issue=5542 |pages=578–580}}</ref>

[[Subduction]] due to plate tectonics would have removed carbonate from the early oceans, contributing to the removal of the {{chem|CO|2}}-rich early atmosphere. Removal of this early atmosphere is evidence of Hadean plate tectonics.<ref name=Sleep2014>{{cite journal |last1=Sleep |first1=NH |last2=Zahnle |first2=KJ |last3=Lupu |first3=RE |year=2014 |title=Terrestrial aftermath of the Moon-forming impact |journal=Phil. Trans. R. Soc. A |doi=10.1098/rsta.2013.0172 |pmid=25114303 |bibcode=2014RSPTA.37230172S |s2cid=6902632 |volume=372 |issue=2024 |page=20130172|doi-access=free }}</ref>

If plate tectonics occurred in the Hadean, it would have formed [[continental crust]].<ref name=Guo2020>{{cite journal |last1=Guo |first1=M |last2=Korenaga |first2=J |year=2020 |title=Argon constraints on the early growth of felsic continental crust |journal=Science Advances |doi=10.1126/sciadv.aaz6234 |pmid=32671213 |pmc=7314546 |bibcode=2020SciA....6.6234G |volume=6 |issue=21 |page=eaaz6234}}</ref> Different models predict different amounts of continental crust during the Hadean.<ref name=Harrison2009>{{cite journal|last=Harrison|first=TM|title=The Hadean crust: evidence from> 4 Ga zircons|journal=Annual Review of Earth and Planetary Sciences|volume=37|year=2009|issue=1 |pages=479–505|doi=10.1146/annurev.earth.031208.100151 |bibcode=2009AREPS..37..479H }}</ref> The work of Dhiume ''et al.'' predicts that by the end of the Hadean, the continental crust had only 25% of today's area.<ref name=Dhuime2012>{{cite journal |last1=Dhuime |first1=B |last2=Hawkesworth |first2=CJ |last3=Cawood |first3=PA |last4=Storey |first4=CD |year=2012 |title=A change in the geodynamics of continental growth 3 billion years ago |journal=Science |doi=10.1126/science.1216066 |pmid=22422979 |bibcode=2012Sci...335.1334D |s2cid=206538532 |volume=335 |issue=6074 |pages=1334–1336}}</ref> The models of Korenaga, ''et al.'' predict that the continental crust grew to present-day volume sometime between 4.2 and 4.0 [[Gya (unit)|Gya]].<ref name=Guo2020/><ref>{{cite journal |last1=Rosas |first1=JC |last2=Korenaga |first2=J |year=2018 |title=Rapid crustal growth and efficient crustal recycling in the early Earth: Implications for Hadean and Archean geodynamics |journal=Earth Planet. Sci. Lett. |doi=10.1016/j.epsl.2018.04.051 |bibcode=2018E&PSL.494...42R |s2cid=13666395 |volume=494 |pages=42–49|doi-access=free }}</ref>

==Continents==
The amount of exposed land in the Hadean is only loosely dependent on the amount of continental crust: it also depends on the ocean level.<ref name=Korenaga2021/> In models where plate tectonics started in the Archean, Earth has a global ocean in the Hadean.<ref>{{cite journal |last=Russell |first=MJ |year=2021 |title=The "Water Problem", the illusory pond and life's submarine emergence—A review |journal=Life |doi=10.3390/life11050429 |doi-access=free |pmid=34068713 |pmc=8151828 |volume=11 |issue=5 |page=429|bibcode=2021Life...11..429R }}</ref><ref>{{cite journal |last=Voosen |first=P |year=2021 |title=Ancient Earth was a water world |journal=Science |doi=10.1126/science.371.6534.1088 |pmid=33707245 |bibcode=2021Sci...371.1088V |s2cid=232206926 |volume=371 |issue=6534 |pages=1088–1089}}</ref> The high heat of the mantle may have made it difficult to support high elevations in the Hadean.<ref>{{cite journal |last1=Monteux |first1=J |last2=Andrault |first2=D |last3=Guitreau |first3=M |last4=Samuel |first4=H |last5=Demouchy |first5=S |year=2020 |title=A mushy Earth's mantle for more than 500 Myr after the magma ocean solidification |journal=Geophys. J. Int. |doi=10.1093/gji/ggaa064 |volume=221 |issue=2 |pages=1165–1181|doi-access=free }}</ref><ref>{{cite journal |last1=Rey |first1=PF |last2=Coltice |first2=N |year=2008 |title=Neoarchean lithospheric strengthening and the coupling of Earth's geochemical reservoirs |journal=Geology |doi=((10.1130/G25031A.1;)) |bibcode=2008Geo....36..635R |volume=36 |issue=8 |pages=635–638}}</ref> If continents did form in the Hadean, their growth competed with outgassing of water from the mantle.<ref name=Korenaga2021/> Continents may have appeared in the mid-Hadean, and then disappeared under a thick ocean by the end of the Hadean.<ref>{{cite journal |last1=Bada |first1=JL |last2=Korenaga |first2=J |year=2018 |title=Exposed areas above sea level on Earth >3.5 Gyr ago: Implications for prebiotic and primitive biotic chemistry |journal=Life |doi=10.3390/life8040055 |doi-access=free |pmid=30400350 |pmc=6316429 |volume=8 |issue=4 |page=55|bibcode=2018Life....8...55B }}</ref> The limited amount of land has implications for the [[origin of life]].<ref name=Korenaga2021/>

==Possible life==

Abundant Hadean-like [[Geothermal activity|geothermal]] [[Microenvironment (ecology)|microenvironment]]s were shown by Salditt ''et al.'' to have the potential to support the synthesis and replication of [[RNA]] and thus possibly the evolution of a primitive life form.<ref name = Salditt2023>{{cite journal|last1=Salditt|first1=A|last2=Karr|first2=L|last3=Salibi|first3=E|last4=Le Vay|first4=K|last5=Braun|first5=D|last6=Mutschler|first6=H|title=Ribozyme-mediated RNA synthesis and replication in a model Hadean microenvironment|journal=Nat. Commun.|date=2023-03-17|volume=14|issue=1|page=1495|doi=10.1038/s41467-023-37206-4|pmid=36932102|pmc=10023712|bibcode=2023NatCo..14.1495S}}</ref>  Porous rock systems comprising heated air-water interfaces were shown to allow [[ribozyme]]-[[Catalysis|catalyzed]] RNA replication of sense and antisense strands followed by subsequent strand dissociation, thus enabling combined synthesis, release and folding of active ribozymes.<ref name = Salditt2023/> 
A study published in 2024 inferred the [[Last universal common ancestor|last common ancestor of all current life]] to have emerged during the Hadean, between 4.09 and 4.33 Gya.<ref>{{cite journal |last1=Moody |first1=Edmund |last2=Álvarez-Carretero |first2=Sandra |last3=Mahendrarajah |first3=Tara |title=The nature of the last universal common ancestor and its impact on the early Earth system |journal=Nat. Ecol. Evol. |date=12 July 2024 |volume=8 |issue=9 |pages=1654–1666 |doi=10.1038/s41559-024-02461-1 |doi-access=free |pmid=38997462 |pmc=11383801 |bibcode=2024NatEE...8.1654M }}</ref>

Although the early part of the [[Late Heavy Bombardment]] happened during the Hadean, the impacts were frequent only on a cosmic scale, with thousands or even millions of years between each event. As Earth already had oceans, life would have been possible, but vulnerable to [[extinction event]]s caused by those impacts. The risk would not be on the frequency, but on the size of the impactor, and remains on the Moon suggest impactors bigger than the [[Chicxulub impactor]] that caused the [[Cretaceous–Paleogene extinction event|extinction of dinosaurs]]. An impactor big enough may erase all life on the planet, although some models suggest that microscopic life may still survive if underground or in the oceanic depths.<ref>{{cite book |last=Bennett |first=Jeffrey |author-link= |date=2017 |title=Life in the universe |url= |location=United States |publisher=Pearson |pages=124–125 |isbn=978-0-13-408908-9}}</ref>

==See also==
* {{annotated link|Chaotian (geology)}}
* {{annotated link|Faint young Sun paradox}}
* [[Formation and evolution of the Solar System]]
* {{annotated link|Hadean zircon}}
* {{annotated link|History of Earth}}&nbsp;– the first sections describe the formation of Earth
* {{annotated link|Oldest dated rocks}}
* {{annotated link|Precambrian}}
* {{annotated link|Timeline of natural history}}

==References==
{{reflist}}

==Further reading==
*{{cite journal |last1=Hopkins |first1=Michelle |last2=Harrison |first2=T. Mark |last3=Manning |first3=Craig E. |year=2008 |title=Low heat flow inferred from >4 Gyr zircons suggests Hadean plate boundary interactions |journal=[[Nature (journal)|Nature]] |doi=10.1038/nature07465 |pmid=19037314 |bibcode=2008Natur.456..493H |s2cid=4417456|volume=456 |issue=7221 |pages=493–496}}
*{{cite journal |last1=Wyche |first1=S. |last2=Nelson |first2=D. R. |last3=Riganti |first3=A. |year=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 |doi=10.1046/j.1400-0952.2003.01042.x |bibcode=2004AuJES..51...31W |volume=51 |issue=1 |pages=31–45}}
*{{cite journal |last1=Carley |first1=Tamara L. |last2=Miller |first2=Calvin F. |last3=Wooden |first3=Joseph L. |last4=Padilla |first4=Abraham J. |last5=Schmitt |first5=Axel K. |last6=Economos |first6=Rita C. |last7=Bindeman |first7=Ilya N. |last8=Jordan |first8=Brennan T. |display-authors=1 |year=2014 |title=Iceland is not a magmatic analog for the Hadean: Evidence from the zircon record |journal=Earth and Planetary Science Letters |doi=10.1016/j.epsl.2014.08.015 |bibcode=2014E&PSL.405...85C |volume=405 |issue=1 |pages=85–97}}
*{{cite journal |last1=Marchi |first1=S. |last2=Bottke |first2=W. F. |last3=Elkins-Tanton |first3=L. T. |last4=Bierhaus |first4=M. |last5=Wuennemann |first5=K. |last6=Morbidelli |first6=A. |last7=Kring |first7=D. A. |display-authors=1 |year=2014 |title=Widespread mixing and burial of Earth's Hadean crust by asteroid impacts |journal=Nature |doi=10.1038/nature13539 |volume=511 |issue=7511 |pages=578–582|pmid=25079556 |bibcode=2014Natur.511..578M |s2cid=205239647 }}

==External links==
{{Commons}}
*[https://web.archive.org/web/20071103114128/http://www.peripatus.gen.nz/paleontology/Hadean.html Peripatus.nz: Description of the Hadean Era]
*[https://ghkclass.com/ghkC.html?hadean Hadean (chronostratigraphy scale)]

{{Hadean Footer}}
{{Geological history|c}}
{{Authority control}}

[[Category:Hadean| ]]
[[Category:Precambrian geochronology]]