[prot-er-uh-zoh-ik, proh-ter-] Geology.
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.

1905–10; protero- + zo- + -ic Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
Proterozoic (ˌprəʊtərəʊˈzəʊɪk)
1.  Compare Archaeozoic the later of two divisions of the Precambrian era, during which the earliest plants and animals are assumed to have lived
2.  of or formed in the late Precambrian era

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
Proterozoic   (prŏt'ər-ə-zō'ĭk)  Pronunciation Key 
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.
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Example sentences for proterozoic
The first organisms having features typical of fungi date to , the proterozoic.
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