from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. 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.
- n. The Proterozoic Eon.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. 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.
- proper n. The Proterozoic eon.
from The Century Dictionary and Cyclopedia
- Of or pertaining to the life existing before the time of the Cambrian or first fossils: a term originally proposed as a substitute for Azoic, Eozoic, Archæan, etc., in order to avoid the assertions contained in these words if taken literally.
- n. The time during which the simplest life-forms were developed: applied to the interval between the Archeozoic and Paleozoic as used by Chamberlin and Salisbury. It is assumed that life existed, but no determinable forms have yet been found. The subdivisions of the Proterozoic are Keweenawan, Animikean, and Huronian.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. from 2,500 to 544 million years ago; bacteria and fungi; primitive multicellular organisms
- adj. formed in the later of two divisions of the Precambrian era
Greek proteros, earlier, former; + -zoic.(American Heritage® Dictionary of the English Language, Fourth Edition)