In the geologic timescale, the Eoarchean or EA was an era that lasted from about 4600 MYA to 3600 MYA. It is the first part of the Archaean eon and the first part of the Precambrian eon. During this era, prokaryotes (simple single-celled life) are thought to have originated. The Hadean eon was a part of the Eoarchean, from around 4560 MYA to 3900 MYA. In chronostratigraphy, ts zone rank is an erathem.
The Eoarchean was followed by the Paleoarchean era.
The name comes from two Greek words: eon (dawn) and archios (ancient).