Eoarchean

{{Infobox geologic timespan

| name = {{Color|White|Eoarchean}}

| color = Eoarchean

| top_bar = all time

| time_start = 4031

| time_start_uncertainty = 3

| time_end = 3600

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| timeline = Eons

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| name_formality = Formal

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| alternate_spellings = Eoarchaean

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| celestial_body = earth

| usage = Global (ICS)

| timescales_used = ICS Time Scale

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| chrono_unit = Era

| strat_unit = Erathem

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| timespan_formality = Formal

| lower_boundary_def = Ten oldest U-Pb zircon ages

| lower_gssa_accept_date = 2023{{cite web |title=Global Boundary Stratotype Section and Point |url=https://stratigraphy.org/gssps/ |publisher=International Commission of Stratigraphy |access-date=29 October 2023}}

| upper_boundary_def = Defined Chronometrically

| upper_gssa_accept_date = 1991{{citation needed|date=February 2023|reason=Previously given Plumb 1991 reference was not about the Eoarchean but only the introduction of the Archean Eon. It even said that further sub-division of the Archean was deferred to a later date.}}

|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, Greenland. ]]

File:Garnet paragneiss Nuvvuagittuq Greenstone Belt, 4.28 Ga.jpg, 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 of the Archean Eon of the geologic record. It spans 431 million years, from the end of the Hadean Eon 4031 Mya to the start of the Paleoarchean Era 3600 Mya.

Some estimates place the beginnings of life on Earth in this era, while others{{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 }} place it earlier. Evidence of archaea and cyanobacteria date to 3500 Mya, comparatively shortly after the Eoarchean. At that time, the atmosphere was without oxygen and the pressure values ranged from 10 to 100 bar (around 10 to 100 times the atmospheric pressure today).{{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 }}{{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}}{{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}}

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 Archaean Eon, preceded by the Hadean Eon, during which the Earth is believed to have been essentially molten.

The Eoarchaean's lower boundary or starting point of 4.031 Gya (4031 million years ago) is officially recognized by the International Commission on Stratigraphy.{{cite web |date=September 2023 |title=International Chronostratigraphic Chart v.2023/09 |publisher=International Commission on Stratigraphy |url=http://www.stratigraphy.org/ICSchart/ChronostratChart2023-09.pdf |access-date=October 29, 2023}}

The name comes from two 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

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 in northern Québec, Canada, which has been dated to be {{Ma|4280}}.{{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 |doi=10.1126/science.1161925 |pmid=18818357 |bibcode=2008Sci...321.1828O |s2cid=206514655 |volume=321 |issue=5897 |pages=1828–1831}} These formations are presently under intense investigation.{{clarify|date=June 2021}}{{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}} Oxygen isotope ratios show that the hydrological cycle had begun by the early Eoarchaean and possibly earlier.{{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}} 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.{{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 }}

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.{{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}}{{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{{cite book |last=Van Kranendonk |first=Martin J. |others= |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}}

References

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)]

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Category:Geological eras

Category:Precambrian geochronology