Permian Period

Permian Period, last division of the Palaeozoic Era of the geological timescale, spanning an interval of 42 million years, from 295 million to 253 million years ago. It was preceded by the Carboniferous Period, and succeeded by the Triassic, the first period of the Mesozoic Era. The Permian Period was named in 1841 by the English geologist Sir Roderick Impey Murchison after Perm, a city in the Urals, Russia, where sediments of this age were correlated, on the basis of their fossil content, with strata farther west in Germany. In many parts of the world, rocks of Permian age are rich in deposits of oil, gas, and salt.

The latter part of the Palaeozoic was a time of widespread crustal movement. Uplift raised the continental margins from beneath the shallow seas that predominated during the preceding Carboniferous. Deposits that had accumulated in deep troughs were squeezed together and thrust upwards 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 Gondwana. In this way, all the Earth's landmasses were joined in one supercontinent, called Pangaea, named by the German scientist Alfred Wegener. The southern regions of South America and Africa were clustered near the South Pole, together with Antarctica, Australia, and India. By contrast, North America and westernmost Europe straddled the Permian equator and were hot, dry regions, as indicated by thick deposits of evaporite minerals (salt and gypsum) that were precipitated from the waters of enclosed seas. In north-west Europe, marls, limestones and evaporites formed in the shallow Zechstein Sea (including the Magnesian Limestone of north-east England), are characteristic of the period. Beneath these marine Zechstein deposits are the Rothliegende sandstones forming the main commercial gas reservoirs in the southern North Sea.

Permian rocks contain a rich fossil record. On land, seed ferns were joined by conifers and ginkgos as important members of the flora. 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. For the most part, the invertebrate marine life during the Early Permian was exceptionally rich, flourishing in the warm, shallow seas. Larger foraminifera (called fusulines), in particular, were widespread and make extremely useful zonal fossils for correlation purposes in limestone facies. Towards the end of the Permian, however, an important episode of mass extinction—the greatest in all Earth history—occurred. This extinction, the cause of which is still unclear, killed off large groups of corals, bryozoans (see Moss Animals), arthropods, molluscs, echinoderms, and other invertebrates inhabiting the sea.