Proterozoic

Prot·er·o·zo·ic  (prtr--zk, prtr-)

adj.

Of or relating to the later of the two divisions of Precambrian time, from approximately 2.5 billion to 570 million years ago, marked by the buildup of oxygen and the appearance of the first multicellular eukaryotic life forms. See Table at geologic time.

n.

The Proterozoic Eon.

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[Greek proteros, earlier, former; see per¹ in Indo-European roots + -zoic.]

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Proterozoic  (prtr--zk)

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.

Thesaurus

Noun	1.	Proterozoic - from 2,500 to 544 million years ago; bacteria and fungi; primitive multicellular organisms Proterozoic aeon, Proterozoic eon Precambrian, Precambrian aeon, Precambrian eon, Precambrian period - the eon following the Hadean time and preceding the Phanerozoic eon; from about 3,800 million years ago until 544 million years ago
Adj.	1.	proterozoic - formed in the later of two divisions of the Precambrian era; "proterozoic life forms" geology - a science that deals with the history of the earth as recorded in rocks early - at or near the beginning of a period of time or course of events or before the usual or expected time; "early morning"; "an early warning"; "early diagnosis"; "an early death"; "took early retirement"; "an early spring"; "early varieties of peas and tomatoes mature before most standard varieties"