The Eoarchean ( ; also spelled Eoarchaean) is the first era of the Archean of the geologic record. It spans 431 million years, from the end of the Hadean Eon 4031 annum to the start of the Paleoarchean Era 3600 Mya.
Some estimates place the abiogenesis of life on Earth in this era, while others
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 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.
The name comes from two Greek language words: (dawn) and (ancient). The first supercontinent candidate Vaalbara appeared around the end of this period at about .
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
Quebec, which has been dated to be .
These formations are presently under intense investigation.
Oxygen isotope ratios show that the
Water cycle had begun by the early Eoarchaean and possibly earlier.
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.
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.
Proposed subdivisions
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Eoarchean Era — 4031–3600 Mya
-
Acastan Period — 4031–3810 Mya
-
Isuan Period — 3810–3600 Mya
See also
Further reading
External links
