Span of geologic time from 542 million years ago, the end of the Proterozoic Eon, to the present. The Phanerozoic, the eon of visible life, is divided into three major eras: the Paleozoic, Mesozoic, and Cenozoic. Although life originated in Precambrian time, it was in the Phanerozoic that many forms arose and evolved. The Earth gradually assumed its present configuration and physical features through such processes as plate tectonics, mountain building, and glaciation.
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