Eoarchean

The Eoarchean (pronunciation: /ˌiːoʊ.ɑːrˈkiːən/; also spelled Eoarchaean) is the first era of the Archean Eon of the geologic record for which the Earth has a solid crust. It spans 400 million years from the end of the Hadean Eon 4000 million years ago (Mya) to the start of the Paleoarchean Era 3600 Mya. The abiotic origins of life have been dated to this era and evidence of cyanobacteria date to 3500 Mya, just outside of this era. At that time atmosphere was without oxygen pressure values ranged from 10 to 100 bar (a bit less than 10 to 100 atmospheres).

The Eoarchean was formerly officially unnamed and informally referred to as the first part of the Early Archean or Paleoarchean Era, both now obsolete names.

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 Gya (4 billion years ago) is officially recognized by the International Commission on Stratigraphy.

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