In the geologic record the Eoarchean erathem (pronounced /ˌiː.oʊ.ɑrˈkiː.ən/, also spelled Eoarchaean) and the Eoarchean era in the geologic timescale correspond to one another in the dual system of classification of rock strata laid down beginning 4000 Ma to 3600 Ma (million years ago).

It was formerly officially unnamed and usually referred to as the first part of the Early Archean (now an obsolescent name) together with the later Paleoarchean era. It is the first part of the Archaean Eon, preceded by the "informal" Hadean eon, during which the Earth was considered to be essentially molten.

The International Commission on Stratigraphy currently does not recognize the lower boundary of the era which they've provisionally placed at 4000 Ma^[1] nor that of the preceding Hadean Eon.

The Eoarchean was followed by the Paleoarchean era.

The name comes from two Greek words: eos (dawn) and archios (ancient). The first supercontinent Vaalbara appeared around the end of this period around 3600 ma.

Some interpretations of the the fossil record suggest prokaryote forms may have evolved from protobionts late in this era.

Also the oldest rock formation on earth the Isua greenstone belt appeared during the Eoarchean around 3.8 Billion years ago.

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• A short fact sheet

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