Definition of Proterozoic
: of, relating to, or being the eon of geologic time or the corresponding segment of rocks that includes the interval between the Archean and Phanerozoic eons, exceeds in length all of subsequent geologic time, and is marked by rocks that contain fossils indicating the first appearance of eukaryotic organisms (as algae) — see geologic time table
Origin and Etymology of proterozoic
Greek proteros former, earlier (from pro before) + International Scientific Vocabulary -zoic — more at for
First Known Use: 1899
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