Archean

Archean, also spelled archaean, and also called azoic, is a term in geology for an eon constituting the earlier and middle part of the Precambrian when there was no life on earth. It began from the origin of the earth to about 2,500 million years ago. However, in models that include the Priscoan eon, the Archean is said to began around 4,000 million years ago. It precedes the Proterozoic eon. It was during the Archean, the system of rocks deposited.

Anything of, relating to, or denoting the Archean is also called archean.