ARCHEAN

I. adjective

or ar·chae·an (ˈ)är|kēən, ˈäṟk-

Usage: usually capitalized

Etymology: Greek archai os ancient + English -an — more at archae-

: of, belonging to, or contemporary with the oldest known group of rocks, usually with the earlier portion of the Precambrian ; sometimes : precambrian — see geologic time table

II. noun

or archaean “

( -s )

Usage: usually capitalized

: the Archean era or system of rocks