Information AboutPermian |
| CATEGORIES ABOUT PERMIAN | |
| permianpermian | |
| paleozoic | |
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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 . SUBDIVISIONS The three primary subdivisons of the Permian Period are given below from youngest to oldest, and include Faunal Stage s also from youngest to oldest. Additional age/stage equivalents or subdivisions are given in parentheses. Note that ''epoch'' and ''age'' refer to time, and equivalents ''series'' and ''stage'' refer to the rocks. Lopingian Epoch :Changhsingian Age (Djulfian/Ochoan/Dewey Lake/Zechstein) :Wuchiapingian Age (Dorashamian/Ochoan/Longtanian/Rustler/Salado/Castile/Zechstein) Guadalupian Epoch :Capitanian Age (Kazanian/Zechstein) :Wordian Age (Kazanian/Zechstein) :Roadian Age (Ufimian/Zechstein) Cisuralian Epoch :Kungurian Age (Irenian/Filippovian/Leonard/Rotliegendes) :Artinskian Age (Baigendzinian/Aktastinian/Rotliegendes) :Sakmarian Age (Sterlitamakian/Tastubian/Leonard/Wolfcamp/Rotliegendes) :Asselian Age (Krumaian/Uskalikian/Surenian/Wolfcamp/Rotliegendes) OCEANS Sea Level s in the Permian remained generally low, and near-shore environments were limited by the collection of almost all major Landmass es 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 . 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 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 hypothesis 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). Of course, there are species that can metabolize hydrogen sulfide. An even more speculative hypothesis is that intense radiation from a nearby Supernova was responsible for the extinctions. Trilobite s, which had thrived since Cambrian times, finally became extinct before the end of the Permian. LIFE Terrestrial life in the Permian included diverse Plant s, Arthropod s, and various types of Tetrapods . These included Amphibians , Sauropsid s and Synapsid s ( Pelycosaur s and Therapsid s). 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 Thecodont s); during the following, Triassic , period these latter would evolve into more advanced types, eventually into Dinosaur s. 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 Ginkgo s and Cycad s 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 Mollusk s, Echinoderm s, and Brachiopod s. Fossilized shells of two kinds of s, a kind of shelled amoeba-like Protist that is one of the Foraminifera ns, and Ammonoids , shelled Cephalopod s 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. Desert s seem to have been widespread on Pangea. Such dry conditions favored Gymnosperm s, plants with Seed s enclosed in a protective cover, over plants such as Fern s that disperse Spore s. The first modern Tree s ( Conifers , Ginkgo s and Cycad s) 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. SEE ALSO REFERENCES
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