Eoarchean

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Eoarchean
4031 ± 3 – 3600 Ma
Chronology
Eoarchaean (3.8 b.y.) Greenlandite specimen (fuchsite-quartz gneiss), Nuup Kangerlua, Greenland.
paragneiss
, Nuvvuagittuq Greenstone Belt, Canada. 4.28 Ga old: the oldest known Earth rock of which direct samples are available.

The Eoarchean (

Mya to the start of the Paleoarchean Era 3600 Mya. The beginnings of life on Earth have been dated to this era and 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).[2][3][4]

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

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.[5]

The name comes from two Greek words: eos (dawn) and archaios (ancient). The first supercontinent candidate Vaalbara appeared around the end of this period at about 3,600 million years ago.

Geology

The beginning of the Eoarchean is characterized by heavy

Nuvvuagittuq Greenstone Belt in northern Québec, Canada, which has been dated to be 4,280 million years ago.[6] These formations are presently under intense investigation.[clarification needed][7] Carbonate precipitation (caused by heating of sea water by hydrothermal vents) acted as an important sink regulating the concentration of carbon dioxide in the atmosphere during this era.[8]

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.[9][needs update?]

Proposed subdivisions

  • Eoarchean Era — 4031–3600 Mya
    • Acastan Period — 4031–3810 Mya
    • Isuan Period — 3810–3600 Mya[10]

See also

References

  1. ^ "Global Boundary Stratotype Section and Point". International Commission of Stratigraphy. Retrieved 29 October 2023.
  2. PMID 19703272
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  5. ^ "International Chronostratigraphic Chart v.2023/09" (PDF). International Commission on Stratigraphy. September 2023. Retrieved October 29, 2023.
  6. S2CID 206514655
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Further reading

External links