Source : WordNet®

Archean
     n : 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}]