Permian
The Permian as a geologic period that extends from about 280 to 251 million years before the present. As with most older geologic periods, the strata that define the start and end are well identified, but the exact date of the start of the period is uncertain by a few million years. The end of the period is marked by a major extinction event that is more tightly dated. The Permian is named from the extensive exposures in the region around the city of Perm in Russia. The Permian follows the Carboniferous (Pennsylvanian in North America) and is followed by the Triassic. Permian exposures consist largely of continental redbeds and shallow water marine exposures.
The Permian is usually broken into Lower (early) and Upper (late) subdivisions. The faunal stages from youngest to oldest are:
- Changxingian/Lopingian/Djulfian/Ochoan/Dewey Lake (Zechstein)
- Wujiapingian/Lopingian/Dorashamian/Ochoan/Longtanian/Rustler/Salado/Castile (Zechstein)
- Capitanian/Guadelupian/Kazanian (Zechstein)
- Wordian/Guadelupian/Kazanian (Zechstein)
- Roadian/Ufimian/Guadelupian (Zechstein)
- Kungurian/Irenian/Filippovian/Leonard (Rotliegendes)
- Artinskian/Baigendzinian/Aktastinian (Rotliegendes)
- Sakmarian/Sterlitamakian/Tastubian/Leonard/Wolfcamp (Rotliegendes)
- Asselian/Krumaian/Uskalikian/Surenian/Wolfcamp (Rotliegendes)
Sea levels in the Permian remained generally low and near-shore environments were limited by the collection of almost all major landmasses into a single continent -- Pangea. One continent - even a large continent - has less shoreline than six to eight smaller ones.
The Permian ended with the most extensive extinction event recorded in paleontology: the Permian-Triassic extinction event. 90% to 95% of marine species became extinct, as well as 70% of all organisms on land. There is very modest evidence that the extinction could have been caused by climate changes due to impact by a large bolide. Land life in the Permian included diverse plants, large amphibians and large reptiles including the ancestors of the dinosaurs. Permian marine deposits are rich in mollusks, echinoderms, and brachiopods. The last trilobites died out before the end of the Permian. Fossilized shells of two kinds of inverebrates are widely used to identify Permian strata and correlate them between sites: fusulinids, a kind of shelled amoeba-like protist that is one of the foraminiferans, and ammonoids, whose modern relatives are the Nautilus.
During the Permian, all the Earth's major land masses except portions of East Asia were collected into a single supercontinent known as Pangea. Pangea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean ("Panthalassa", the "universal sea"). Large continental landmasses create climates with extreme variations of heat and cold ("continental climate") and monsoon conditions, with highly seasonal rainfall patterns. Deserts seem to have been widespread in Pangea. Dry conditions favored gymnosperm plants, with seeds that are enclosed in a protective cover, over plants, such as ferns, that disperse spores. The first modern trees (conifers, ginkgos and cycads) appeared in the Permian.
Three general areas are especially noted for their Permian deposits: the Ural Mountains (where Perm itself is located), China, and the southwest of North America, where the Permian Basin in the U.S. state of Texas is so named because it has one of the thickest deposits of Permian rocks in the world.
