View source for Eoarchean

{{Short description|First era of the Archean Eon}}
{{Infobox geologic timespan
| name                         = {{Color|White|Eoarchean}}
| color                        = Eoarchean
| top_bar                      = all time
| time_start                   = {{period start|eoarchean}}
| time_start_uncertainty       = 3
| time_end                     = {{period end|eoarchean}}
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<!--Chronology-->
| timeline                     = Eons
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<!--Etymology-->
| chrono_name                  =
| strat_name                   =
| name_formality               = Formal
| name_accept_date             =
| alternate_spellings          = Eoarchaean
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| celestial_body               = earth
| usage                        = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used              = ICS Time Scale
| formerly_used_by             =
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<!--Definition-->
| chrono_unit                  = Era
| strat_unit                   = Erathem
| proposed_by                  =
| timespan_formality           = Formal
| lower_boundary_def           = Ten oldest U-Pb zircon ages
| lower_gssa_accept_date       = {{period start ratification|eoarchean}}
| upper_boundary_def           = Defined Chronometrically
| upper_gssa_accept_date       = {{period end ratification|eoarchean}}
|lower_gssa_location=Along the Acasta River, [[Northwest Territories]], [[Canada]]|lower_gssa_coords={{Coord|65.1738|N|115.5538|W|display=inline}}}}
[[File:Greenlandite (fuchsite-quartz gneiss), Greenland.jpg|thumb|Eoarchaean (3.8 b.y.) Greenlandite specimen (fuchsite-quartz gneiss), [[Nuup Kangerlua]], Greenland. ]]
[[File:Garnet paragneiss Nuvvuagittuq Greenstone Belt, 4.28 Ga.jpg|thumb|Garnet [[paragneiss]], Nuvvuagittuq Greenstone Belt, Canada. 4.28 Ga old: the oldest known Earth rock of which direct samples are available. ]]
The '''Eoarchean''' ({{IPAc-en|ipa|ˌ|iː|oʊ|.|ɑɹ|ˈ|k|iː|ə|n}} {{respell|EE|oh|ar|KEE|ən}}; also spelled '''Eoarchaean''') is the first [[Era (geology)|era]] of the [[Archean|Archean Eon]] of the [[geologic record]]. It spans 431 million years, from the end of the Hadean Eon 4031 [[annum|Mya]] to the start of the [[Paleoarchean]] Era 3600 Mya. 
Some estimates place the [[abiogenesis|beginnings]] of [[Earliest known life forms|life on Earth]] in this era, while others<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 |doi=10.1038/s41559-024-02461-1 |url=https://www.nature.com/articles/s41559-024-02461-1 |access-date=26 August 2024|doi-access=free |pmc=11383801 }}</ref> place it earlier. Evidence of [[archaea]] and [[cyanobacteria]] date to 3500 Mya, comparatively shortly after the Eoarchean. At that time, the [[Atmosphere of Earth|atmosphere]] was without [[oxygen]] and the pressure values ranged from 10 to 100 [[Bar (unit)|bar]] (around 10 to 100 times the atmospheric pressure today).<ref>{{cite journal |last=Mulkidjanian |first=Armen Y. |date=August 2009 |title=On the origin of life in the zinc world: 1. Photosynthesizing, porous edifices built of hydrothermally precipitated zinc sulfide as cradles of life on Earth |journal=Biol. Direct |doi=10.1186/1745-6150-4-26 |pmid=19703272 |pmc=3152778 |volume=4 |pages=26– |doi-access=free }}</ref><ref>{{cite journal |last1=Mulkidjanian |first1=A. Y. |last2=Bychkov |first2=A. Y. |last3=Dibrova |first3=D. V. |last4=Galperin |first4=M. Y. |last5=Koonin |first5=E. V. |year=2012 |title=Origin of first cells at terrestrial, anoxic geothermal fields |journal=Proc. Natl. Acad. Sci. USA |doi=10.1073/pnas.1117774109 |doi-access=free |bibcode=2012PNAS..109E.821M |pmid=22331915 |pmc=3325685 |volume=109 |issue=14 |pages=E821–30}}</ref><ref>{{cite encyclopedia |last=Mulkidjanian |first=A. Y. |editor1-last=Egel |editor1-first=R. |editor2-last=Lankenau |editor2-first= D.-H. |editor3-first=A. Y. |editor3-last= Mulkidjanian |year=2011 |title=Energetics of the First Life |encyclopedia=Origins of Life: The Primal Self-Organization |publisher=Springer Verlag |location=Heidelberg |isbn=978-3-642-21625-1 |pages=3–33}}</ref>

==Chronology==
The Eoarchean Era was formerly officially unnamed and informally referred to as the first part of the ''Early Archean'' Eon (which is now an obsolete name) alongside the [[Paleoarchean]] Era.

The [[International Commission on Stratigraphy]] now officially recognizes the Eoarchean Era as the
first part of the [[Archean|Archaean]] [[eon (geology)|Eon]], preceded by the [[Hadean]] Eon, during which the Earth is believed to have been essentially molten.<!-- In [[chronostratigraphy]], its zone rank is an [[erathem]]. -->

The Eoarchaean's lower boundary or starting point of 4.031 [[Gya (unit)|Gya]] (4031 [[million years ago]]) is officially recognized by the International Commission on Stratigraphy.{{ref icc}}

The name comes from two [[Greek language|Greek]] words: ''{{Transliteration|el|eos}}'' (dawn) and ''{{Transliteration|el|Archaios}}'' (ancient). The first [[supercontinent]] candidate [[Vaalbara]] appeared around the end of this period at about {{Ma|3600}}.

==Geology==
{{mainarticle|Eoarchean geology}}
The beginning of the Eoarchean is characterized by heavy [[asteroid]] bombardment within the [[Inner Solar System]]: the [[Late Heavy Bombardment]]. The largest Eoarchean rock formation is the [[Isua Greenstone Belt]] on the south-west coast of [[Greenland]], which dates from 3.8 billion years. The [[Acasta Gneiss]] within the [[Canadian Shield]] have been dated to be 4,031 Ma and are therefore the oldest preserved rock formations. In 2008, another rock formation was discovered in the [[Nuvvuagittuq greenstone belt|Nuvvuagittuq Greenstone Belt]] in northern [[Quebec|Québec, Canada]], which has been dated to be {{Ma|4280}}.<ref>{{cite journal |last1=O'Neil |first1=J. |last2=Carlson |first2=R. W. |last3=Francis |first3=D. |last4=Stevenson |first4=R. K. |year=2008 |title=Neodymium-142 Evidence for Hadean Mafic Crust |journal=[[Science (journal)|Science]] |doi=10.1126/science.1161925 |pmid=18818357 |bibcode=2008Sci...321.1828O |s2cid=206514655 |volume=321 |issue=5897 |pages=1828–1831}}</ref> These formations are presently under intense investigation.{{clarify|date=June 2021}}<ref>{{cite journal |last1=David |first1=J. |last2=Godin |first2=L. |last3=Stevenson |first3=R. K. |last4=O'Neil |first4=J. |last5=Francis |first5=D. |date=2009 |title=U-Pb ages (3.8–2.7 Ga) and Nd isotope data from the newly identified Eoarchean Nuvvuagittuq supracrustal belt, Superior Craton, Canada |journal=[[Geological Society of America Bulletin]] |doi=10.1130/B26369.1 |volume=121 |issue=1–2 |pages=150–163}}</ref> Oxygen isotope ratios show that the [[Water cycle|hydrological cycle]] had begun by the early Eoarchaean and possibly earlier.<ref>{{Cite journal |last=Gamaleldien |first=Hamed |last2=Wu |first2=Li-Guang |last3=Olierook |first3=Hugo K. H. |last4=Kirkland |first4=Christopher L. |last5=Kirscher |first5=Uwe |last6=Li |first6=Zheng-Xiang |last7=Johnson |first7=Tim E. |last8=Makin |first8=Sean |last9=Li |first9=Qiu-Li |last10=Jiang |first10=Qiang |last11=Wilde |first11=Simon A. |last12=Li |first12=Xian-Hua |date=3 June 2024 |title=Onset of the Earth’s hydrological cycle four billion years ago or earlier |url=https://www.nature.com/articles/s41561-024-01450-0 |journal=[[Nature Geoscience]] |language=en |volume=17 |issue=6 |pages=560–565 |doi=10.1038/s41561-024-01450-0 |issn=1752-0894 |access-date=16 July 2024|url-access=subscription }}</ref> Carbonate precipitation (caused by heating of seawater by hydrothermal vents) acted as an important sink regulating the concentration of [[carbon dioxide]] in the atmosphere during this era.<ref>{{cite journal |last1=Antonelli |first1=Michael A. |last2=Kendrick |first2=Jillian |last3=Yakymchuk |first3=Chris |last4=Guitreau |first4=Martin |last5=Mittal |first5=Tushar |last6=Moynier |first6=Frédéric |date=5 May 2021 |title=Calcium isotope evidence for early Archaean carbonates and subduction of oceanic crust |journal=[[Nature Communications]] |volume=12 |issue=1 |pages=1–8 |doi=10.1038/s41467-021-22748-2 |doi-access=free |hdl=20.500.11850/484746 |hdl-access=free |pmc=8099908 }}</ref>

==Atmosphere==
3,850 million years old [[apatite]] from Greenland shows evidence of [[Carbon-12]] enrichment. This has sparked a debate whether there might have been photosynthetic life before 3.8 billion years ago.<ref>{{cite journal |last1=Mojzsis |first1=S. J. |last2=Arrhenius |first2=G. |last3=McKeegan |first3=K. D. |last4=Harrison |first4=T. M. |last5=Nutman |first5=A. P. |last6=Friend |first6=C. R. L. |date=1996 |title=Evidence for life on Earth before 3,800 million years ago |journal=Nature |doi=10.1038/384055a0 |pmid=8900275 |bibcode=1996Natur.384...55M |hdl=2060/19980037618 |hdl-access=free |s2cid=4342620 |volume=384 |issue=6604 |pages=55–59 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980037618.pdf}}</ref>{{Update inline|reason=Debate was started at least 25 years ago - has it been resolved?|?=yes|date=September 2021}}

==Proposed subdivisions==
*Eoarchean Era — 4031–3600 Mya
**Acastan Period — 4031–3810 Mya
**Isuan Period — 3810–3600 Mya<ref name=VanKranendonk2012>{{cite book |last=Van Kranendonk |first=Martin J. |others=<!-- there are like 10 contributors--> |editor1-last=Gradstein |editor1-first=Felix M. |editor2-last=Ogg |editor2-first=James G. |editor3-last=Schmitz |editor3-first=Mark D. |editor4-last=Ogg |editor4-first=Gabi M. |date=2012 |title=The geologic time scale 2012 |edition=1st |chapter=16: A Chronostratigraphic Division of the Precambrian: Possibilities and Challenges |publisher=Elsevier |location=Amsterdam |isbn=978-0-44-459425-9 |pages=359–365}}</ref>

==See also==
*[[Precambrian]] Supereon (4600-539 Mya)
**[[Hadean]] Eon (4600-4031 Mya)
**[[Archean]] Eon (4031-2500 Mya)
***[[Paleoarchean]] Era (3600-3200 Mya)
***[[Mesoarchean]] Era (3200-2800 Mya)
***[[Neoarchean]] Era (2800-2500 Mya)
**[[Proterozoic]] Eon (2500-539 Mya)

==References==
{{reflist}}

==Further reading==
* {{cite book |last1=Egel |first1=R. |last2=Lankenau |first2=D.-H. |last3=Mulkidjanian |first3=A. Y. |year=2011 |title=Origins of Life: The Primal Self-Organization |publisher=Springer-Verlag |location=Berlin Heidelberg |isbn=978-3-642-21624-4 |doi=10.1007/978-3-642-21625-1 |url=https://www.springer.com/life+sciences/evolutionary+%26+developmental+biology/book/978-3-642-21624-4}}

==External links==
*{{commonscat-inline|Eoarchean}}
*[https://web.archive.org/web/20160328202942/http://taxonconcept.stratigraphy.net/zone_info.php?zone_id=109&zone_type_id=1&zone_theme_id=100 Taxonconcept.stratigraphy.ne: A short fact sheet on the Eoarchean]
*[https://ghkclass.com/ghkC.html?eoarchean Eoarchean (chronostratigraphy scale)]

{{Archean Footer}}
{{Geological history|c}}

[[Category:Archean|*01]]
[[Category:Geological eras]]
[[Category:Precambrian geochronology]]