Proterozoic
WordNet
adjective
(1) Formed in the later of two divisions of the Precambrian era
"Proterozoic life forms"
noun
(2) From 2,500 to 544 million years ago; bacteria and fungi; primitive multicellular organisms
WiktionaryText
Adjective
- Of, or relating to the geologic eon from about 2,500 to 570 million years ago; comprises the Paleoproterozoic, Mesoproterozoic and Neoproterozoic eras; marked by the build up of oxygen in the atmosphere and the emergence of primitive multicellular life.