Archaeozoic

from The Century Dictionary.

• In geology, having reference to the earliest life-forms found in the rocks: a term introduced by Le Conte and employed by Dana to designate a hypothetical division or eon of Archæan time contradistinguished from the Azoic eon.
• noun The Archæozoic eon.

from the GNU version of the Collaborative International Dictionary of English.

• noun the time from 1.5 billion to 5 billion years ago; the time when the earth's crust formed; a time when only unicellular organisms and the earliest forms of life are present.
• adjective (Zoöl.) Like or belonging to the earliest forms of animal life.
• adjective (Geol.) formed in or belonging to the earlier of two divisions of the Precambrian era.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• proper noun Period of time determined to exist prior to 2.5 thousand million years ago.
• adjective Of or pertaining to the Archaeozoic.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective of or belonging to earlier of two divisions of the Precambrian era
• 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