- of, relating to, or denoting the earliest eon, preceding the Cambrian period and the Phanerozoic eon. Compare with Cryptozoic.
The Precambrian extended from the origin of the earth (believed to have been about 4,600 million years ago) to about 570 million years ago, representing nearly ninety percent of geological time. The oldest known Precambrian rocks have been dated to about 3,800 million years old, and the earliest living organisms date from the latter part of the eon. The Precambrian is now replaced in formal stratigraphic schemes by the Archean, Proterozoic, and (in some schemes) Priscoan eons