|1.||Compare Archaeozoic the later of two divisions of the Precambrian era, during which the earliest plants and animals are assumed to have lived|
|2.||of or formed in the late Precambrian era|
|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.