Archean

Ar che an |ärˈkēən ɑrˈkiən |(Brit. Archaean ) ▶adjective Geology of, relating to, or denoting the eon that constitutes the earlier (or middle ) part of the Precambrian, in which there was no life on earth. It precedes the Proterozoic eon. Also called azoic. • (as noun the Archean ) the Archean eon or the system of rocks deposited during it. The Archean extended from the origin of the earth (see Precambrian ) to about 2,500 million years ago. In models that include the Priscoan eon, the Archean began about 4,000 million years ago. ORIGIN late 19th cent.: from Greek arkhaios ‘ancient ’ + -an .

Archean

Ar |chean ▶adjective US spelling of Archaean.