[prot-er-uh-zoh-ik, proh-ter-] 
Geology| 1. | 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. |
| 2. | the Proterozoic division of geologic time or the rock systems formed then; Algonkian. |
| Prot·er·o·zo·ic (prŏt'ər-ə-zō'ĭk, prō'tər-) 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. [Greek proteros, earlier, former; see per1 in Indo-European roots + -zoic.] |
| 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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