archean adj : used of the earliest known rocks [syn: archaean]

noun

the time from 3,800 million years to 2,500 million years ago; earth's crust formed; unicellular organisms are earliest forms of life [syn: Archean eon, Archean aeon, Archeozoic, Archaeozoic, Archeozoic eon, Archaeozoic aeon]

Source: WordNet (r) 2.0