[ prot-er-uh-zoh-ik, proh-ter- ]
/ ˌprɒt ər əˈzoʊ ɪk, ˌproʊ tər- /


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.

Origin of Proterozoic

First recorded in 1905–10; protero- + zo- + -ic Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

Examples from the Web for proterozoic

British Dictionary definitions for proterozoic

/ (ˌprəʊtərəʊˈzəʊɪk) /


the later of two divisions of the Precambrian era, during which the earliest plants and animals are assumed to have livedCompare Archaeozoic


of or formed in the late Precambrian era
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for proterozoic

[ prŏt′ər-ə-zōĭk ]

The later of the two divisions of the Precambrian Eon, from about 2.5 billion to 540 million years ago. The Proterozoic was characterized by the formation of stable continents, the appearance of abundant bacteria and archaea, and the buildup of oxygen in the atmosphere. By about 1.8 billion years ago the oxygen buildup was significant enough to cause many types of bacteria to die out. At this time eukaryotes, including multicellular algae and the first animals, first appear in the fossil record. See Chart at geologic time.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.