designating or of the geologic eon characterized by the development of sedimentary rock, shallow seas, and the first soft-bodied, marine invertebrates; Precambrian, esp. late Precambrian
See Proterozoic in American Heritage Dictionary 4
(prŏtˌər-ə-zōˈĭk, prōˌtər-)
adjective
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.