Source : WordNet®

Archean eon
     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}, {Archean aeon}, {Archeozoic},
          {Archaeozoic}, {Archeozoic eon}, {Archaeozoic aeon}]