The Eoarchaean (Eoarchean) is the first geological era in the Archaean eon that began 4 billion years ago, and ended 3.6 billion years ago. Before it was the Hadean It is followed by the Palaeoarchaean.

The Eoarchaean is the earliest period of geology after the solidification of Earth's crust. The abiotic origins of life (abiogenesis) have been dated to a time window from 4 to 3.6 billion years ago when atmospheric pressure values ranged from c. 100 to 10 bar.