/prot'euhr euh zoh"ik, proh'teuhr-/ , Geol.
adj.
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.
n.
2. the Proterozoic division of geologic time or the rock systems formed then; Algonkian. See table under geologic time .
[ 1905-10; PROTERO- + ZO- + -IC ]