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Permian

2007 Schools Wikipedia Selection. Related subjects: Geology and geophysics

          Permian is also an alternative name for the Permic languages

   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.
                         Paleozoic era
   Cambrian Ordovician Silurian Devonian Carboniferous Permian

Subdivisions

   The three primary subdivisons of the Permian Period are given below
   from youngest to oldest, and include faunal stages 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 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.

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"), and the Paleo-Tethys Ocean, a
   large ocean that was between Asia and Gondwana. Cimmeria continent
   rifted away from Gondwana and drifting north to Laurasia, causing the
   Paleo-Tethys to shrink. A new ocean was growing on its southern end,
   the Tethys Ocean, an ocean that will dominate much of the Mesozoic Era.
   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.

Life

   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.

   Terrestrial life in the Permian included diverse plants, fungi,
   arthropods, and various types of tetrapods.

   The Permian began with the Carboniferous flora still flourishing. About
   the middle of the Permian there was a major transition in vegetation.
   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. Lycopods and swamp forests still dominated the South China
   continent because it was an isolated continent and it sat near or at
   the equator. Oxygen levels were probably high there. The Permian saw
   the radiation of many important conifer groups, including the ancestors
   of many present-day families. The ginkgos and cycads also appeared
   during this period. Rich forests were present in many areas, with a
   diverse mix of plant groups.

   A number of important new insect groups appeared at this time,
   including the Coleoptera (beetles) and Diptera (flies).

   Permian tetrapods consisted of temnospondyli, lepospondyli and
   batrachosaur amphibians and sauropsids and synapsid (pelycosaurs and
   therapsids) reptiles. This period saw the development of a fully
   terrestrial fauna and the appearance of the first large herbivores and
   carnivores.

   Early Permian terrestrial faunas were dominated by pelycosaurs and
   amphibians, the middle Permian by primitive therapsids such as the
   dinocephalia, and the late Permian by more advanced therapsids such as
   gorgonopsians and dicynodonts. Towards the very end of the Permian the
   first archosaurs appeared ( proterosuchid thecodonts); during the
   following, Triassic, period these latter would evolve into more
   advanced types, eventually into dinosaurs. Also appearaing at the end
   of the Permian were the first cynodonts, which would go on to evolve
   into mammals during the Triassic. Another group of therapsids, the
   therocephalians (such as Trochosaurus), arose in the Middle Permian.

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 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.

   Trilobites, which had thrived since Cambrian times, finally became
   extinct before the end of the Permian.

   In 2006, a group of American scientists from the Ohio State University
   reported evidence for a possible huge meteorite crater ( Wilkes Land
   crater) with a diameter of around 500 kilometers in Antarctica. The
   crater is located at a depth of 1.6 kilometers beneath the ice of
   Wilkes Land in eastern Antarctica. The scientists speculate that this
   impact may have caused the Permian-Triassic extinction event, although
   its age is bracketed only between 100 million and 500 million years
   ago. They also speculate that it may have contributed in some way to
   the separation of Australia from the Antarctic landmass, which were
   both part of a supercontinent called Gondwana.

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