Pronunciation: (prot"ur-u-zō'ik, prō"tur-), [key] Geol.
noting or pertaining to the latter half of the Precambrian Era, from about 2.5 billion to 570 million years ago, characterized by the appearance of bacteria and marine algae; Algonkian.
the Proterozoic division of geologic time or the rock systems formed then; Algonkian. See table under geologic time.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.