archaean

noun1

1. •
   Any organism of the domain Archaea.

adjective3

1. •
   Of, or relating to the geologic eon from about 4,031 to 2,500 million years ago; comprises the Eoarchean, Paleoarchean, Mesoarchean and Neoarchean eras; marked by an atmosphere with little oxygen, the formation of the first continents and oceans and the emergence of simple life.

   • The oldest vestiges of continental crust, which date from the Archaean aeon about 4 billion years ago, are in Acasta in north-west Canada. — 2006
2. •
   Of or relating to Arche, the Muse of beginnings in Greek mythology.
3. •
   Of or relating to the irregular Jovian moon named for Arche.