Permian Period

Permian Period, last division of the Paleozoic Era of the geologic time scale (see Geology), spanning an interval from about 299 million to 251 million years ago. The Permian was preceded by the Carboniferous Period and followed by the Triassic Period. English geologist Sir Roderick Impey Murchison named the Permian after a village in eastern Russia where sedimentary strata of this age were correlated, on the basis of fossil content, with strata farther west in Germany. Throughout the world the rocks of the Permian period are rich in deposits of coal, oil, and gas.

The latter part of the Paleozoic was a time of widespread crustal unrest. Continents were raised from beneath the shallow seas of the preceding Carboniferous period, and deposits that had accumulated in geosynclinal troughs were squeezed together and thrust upward to form mountain ranges: the central and southern Appalachians in North America and the Urals in Russia. Europe and Asia became joined—Siberia with Russia, and China with Siberia—while to the west a collision of continental plates welded North America to the ancestral supercontinent Gondwanaland. In this way, all of Earth's landmasses collected as one, given the name Pangaea by German geophysicist Alfred Wegener. Apparently the southern regions of South America and Africa were clustered near the South Pole together with Antarctica, Australia, and India. North America and westernmost Europe, which straddled the Permian equator, were hot, dry regions, as indicated by thick deposits of evaporite minerals—such as salt and gypsum—that must have precipitated from the waters of enclosed seas. See Plate Tectonics.

The invertebrate marine life of the beginning of the period was exceptionally rich, flourishing in the warm, shallow inland seas. Toward the end of the period, a wave of mass extinctions, the greatest in all of Earth’s history, brought to an end large groups of corals, bryozoans, echinoderms, and other invertebrates. On land, seed ferns were joined by conifers and ginkgoes. Amphibians were declining in number, but reptiles, which had appeared in the preceding period, were undergoing a spectacular evolutionary development of carnivorous and herbivorous, mammal-like forms. Also during the Permian period the forerunners of the dinosaurs appeared. See Paleontology.