Permian
The Permian is a geologic period that extends from about 299.0 Ma to 248.0 Ma (million years before the present; ICS 2004). It is the last period of the Palaeozoic Era. As with most older geologic periods, the strata that define the Permian are well identified, but the exact date of the period's start is uncertain by a few million years. The Permian follows the Carboniferous ( Pennsylvanian in North America) and is followed by the Triassic. The end of the period is marked by a major extinction event, called the Permian-Triassic extinction event, that is more tightly dated. The Permian was named in the 1840s by Sir Roderick Murchison, a British geologist, from the extensive exposures in the region around the city of Perm in Russia. Permian exposures consist largely of continental red beds and shallow water marine exposures. This period introduced Mammal like Reptiles.
| Paleozoic era | |||||
|---|---|---|---|---|---|
| Cambrian | Ordovician | Silurian | Devonian | Carboniferous | Permian |
Subdivisions
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)
Oceans
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 very large one, has less shoreline than six to eight smaller ones. This could have in part caused the widespread extinctions of marine species at the end of the period by severely reducing shallow coastal areas preferred by many marine organisms.
Permian-Triassic extinction event
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 terrestrial organisms. On an individual level, perhaps as many as 99.5% of separate organisms died as a result of the event.
There is very modest evidence that the extinction could have been caused by climate changes due to impact by a large bolide.
There is also significant evidence that massive flood basalts from magma output contributed to environmental stress leading to mass extinction. The reduced coastal habitat and highly increased aridity probably also contributed.
Another theory involves ocean venting of hydrogen sulfide gas. Portions of deep ocean will periodically lose all of its dissolved oxygen allowing bacteria that live without oxygen to flourish and produce hydrogen sulfide gas. If enough hydrogen sulfide accumulates in an anoxic zone, the gas can rise into the atmosphere.
Oxidizing gasses in the atmosphere would destroy the toxic gas but the hydrogen sulfide would soon consume all of the atmospheric gas available to convert it. Hydrogen sulfide levels would increase dramatically over a few hundred years.
Modeling of such an event indicate that the gas would destroy ozone in the upper atmosphere allowing ultraviolet radiation to kill off species that had survived the toxic gas. (Kump, et al, 2005)
Trilobites, which had thrived since Cambrian times, finally became extinct before the end of the Permian.
Life
Terrestrial life in the Permian included diverse plants, arthropods, amphibians and reptiles. These latter were mostly synapsids (pelycosaurs and therapsids). This period saw the development of a fully terrestrial fauna and the appearance of the first large herbivores and carnivores. Towards the very end of the Permian the first archosaurs appeared ( proterosuchid thecodonts); during the following, Triassic, period these would evolve into more advanced types, eventually into dinosaurs.
On land, the swamp-loving lycopod trees of the Carboniferous, such as Lepidodendron and Sigillaria, were replaced by the more advanced conifers, which were better adapted to the changing climatic conditions. The Permian saw the radiation of many important conifer groups, including the ancestors of many present-day families. The ginkgos, cycads, and bennettitaleans also appeared during this period. Rich forests were present in many areas, with a diverse mix of plant groups.
Permian marine deposits are rich in fossil mollusks, echinoderms, and brachiopods. Fossilized shells of two kinds of invertebrates 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, shelled cephalopods that are distant relatives of the modern nautilus.
Paleogeography
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 on Pangea. Such dry conditions favored gymnosperms, plants with seeds 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.