Proterozoic

American  

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

noun

1. 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.

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adjective

1. of or relating to this eon.

Proterozoic British  

/ ˌprəʊtərəʊˈzəʊɪk /

noun

1. the later of two divisions of the Precambrian era, during which the earliest plants and animals are assumed to have lived Compare Archaeozoic

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adjective

1. of or formed in the late Precambrian era

Proterozoic Scientific  

/ prŏt′ər-ə-zō′ĭk /

1. 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.

2. See Chart at geologic time

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Etymology

Origin of Proterozoic

First recorded in 1905–10; protero- + zo- + -ic