[ prot-er-uh-zoh-ik, proh-ter- ]
/ ˌprɒt ər əˈzoʊ ɪk, ˌproʊ tər- /
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the longest geologic eon and the most recent division of Precambrian time, during which the presence of oxygen in Earth’s atmosphere became significant, causing certain life forms to adapt to the use of oxygen and leading to a proliferation of complex multicellular life.
of or relating to this eon.
In effect, this quiz will prove whether or not you have the skills to know the difference between “affect” and “effect.”
Question 1 of 7
The rainy weather could not ________ my elated spirits on my graduation day.
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Formerly Algonkian .
Compare Archean.

Origin of Proterozoic

First recorded in 1905–10; protero- + zo- + -ic
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

How to use Proterozoic in a sentence

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.