Major interval of geologic time extending from 540-245 million years ago. It is the first era of the Phanerozoic Eon. It is a geological era in the earth's history before the Mesozoic and after the Precambrian, marked by the development of fishes, land plants, insects, reptiles, and fernlike trees. The early Paleozoic (probably the first 130 million years) was characterized by widespread ups and downs of the Earth's crust, which resulted in mountain building and geosynclines (downward flexing) in parts of North America, Europe, and Asia. Great seas were formed in the southern areas of the emergent landmasses. Much of North America was covered by a warm shallow sea with many coral reefs. The late Paleozoic, which extended from about 410 to 245 million years ago, saw tremendous changes wrought in the Earth. Both plant and animal life flourished in the great, warm, shallow seas, and the various convolutions of the Earth laid down extensive mineral deposits. Much of the copper, gold, lead, zinc, and other minerals mined today derive from Devonian times in the late Paleozoic. Huge swampy forest regions covered much of the northern continents, and these were repeatedly and suddenly invaded by the seas, which buried the vegetation, then covered it with silt. When the sea subsequently withdrew, the forests revived and were again buried in rhythmic cycles that are now evident in deposits called cyclothems. Heat and pressure transformed the buried vegetation into the oil and coal. During the Devonian Period animal life emerged from the ocean, and various species adapted themselves to breathing air and moving about on land. This happened by way of the amphibians, which evolved in the Carboniferous and Permian periods, and were succeeded by reptiles. The late Paleozoic also saw the beginning of insect life - and fishes and land plants underwent rapid development.