Eoarchean

The Eoarchean (IPA: /ˌiːoʊ.ɑːrˈkiːən/ EE-oh-ar-KEE-ən; also spelled Eoarchaean) is the first era of the Archean Eon of the geologic record.

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 largest Eoarchean rock formation is the Isua Greenstone Belt on the south-west coast of Greenland, which dates from 3.8 billion years.

In 2008, another rock formation was discovered in the Nuvvuagittuq Greenstone Belt in northern Québec, Canada, which has been dated to be 4,280 million years ago.

[clarification needed][8] Oxygen isotope ratios show that the hydrological cycle had begun by the early Eoarchaean and possibly earlier.

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