Permian

From New World Encyclopedia
Paleozoic era (542 - 251 mya)
Cambrian Ordovician Silurian Devonian Carboniferous Permian
Permian period
299 - 251 million years ago


Key events in the Permian period
-300 —
-295 —
-290 —
-285 —
-280 —
-275 —
-270 —
-265 —
-260 —
-255 —
-250 —
 
 
 
 
Asselian
Sakmarian
Artinskian
Kungurian
Roadian
Wordian
Captainian
Changhsin…
 
 
Mass extinction
Mesozoic era
Paleozoic era
Lopingian (Upper Permian)
Guadalupian (Middle Permian)
Cisuralian (Lower Permian)
An approximate timescale of key Permian events.
Axis scale: millions of years ago.

The Permian period is an interval of about 48 million years defined on the geologic time scale as spanning roughly from 299 to 251 million years ago (mya). The period is noteworthy for having Earth's land mass collected into the single super-continent, Pangea, which provided the forms of life with vast areas of dry or seasonally dry land, but, in comparison with the preceding Carboniferous period, provided greatly reduced swampy lands and coastal margins. The fossil record of the Permian period holds the first modern trees (conifers, ginkgos, and cycads), as well as a number of important new insect groups, including the Coleoptera (beetles) and Diptera (true flies). The Permian period saw the development of a fully terrestrial fauna and the appearance of the first large herbivores and carnivores.

The Permian, the last period of the Paleozoic era, is followed by the Triassic period of the Mesozoic era. The boundary between the Permian and Triassic periods is etched indelibly in the geologic record as Earth's most severe mass extinction event, the Permian-Triassic extinction event (P-T or PT) in which during the so-called Great Dying some 90 percent of all marine species and 70 percent of terrestrial vertebrate species went extinct. The Permian period and the Great Dying laid the foundation for the appearance of dinosaurs and mammals in the Mesozoic era that was to follow.

Subdivisions

Permian period (299 - 251 mya)
Cisuralian Guadalupian Lopingian
Asselian | Sakmarian
Artinskian | Kungurian
Roadian | Wordian
Capitanian
Wuchiapingian
Changhsingian

The three primary subdivisions of the Permian period, from youngest to oldest, are the Lopingian epoch, the Guadalupian epoch, and the Cisuralian epoch.

These are presented below, along with the faunal stages, also from youngest to oldest. The faunal stages refer to subdivisions of rock layers based on the fossil record. Additional age/stage equivalents or subdivisions are given in parentheses. Epoch and age are designation that refer to time, while the equivalents series and stage are designations that refer to the rock layers.

Lopingian epoch

Changhsingian stage (Djulfian/Ochoan/Dewey Lake/Zechstein)
Wuchiapingian stage (Dorashamian/Ochoan/Longtanian/Rustler/Salado/Castile/Zechstein)

Guadalupian epoch

Capitanian stage (Kazanian/Zechstein)
Wordian stage (Kazanian/Zechstein)
Roadian stage (Ufimian/Zechstein)

Cisuralian epoch

Kungurian stage (Irenian/Filippovian/Leonard/Rotliegendes)
Artinskian age (Baigendzinian/Aktastinian/Rotliegendes)
Sakmarian stage (Sterlitamakian/Tastubian/Leonard/Wolfcamp/Rotliegendes)
Asselian age (Krumaian/Uskalikian/Surenian/Wolfcamp/Rotliegendes)

Paleogeography

Map of Pangaea

During the Permian, all of the Earth's major land masses, except portions of East Asia, were collected into a single supercontinent known as Pangaea (or Pangea). Pangaea would break apart during the Triassic and Jurassic periods of the Mesozoic, separating into Laurasia and Gondwana (or Gondwanaland).

In configuration, Pangaea is believed to have been a C-shaped landmass that spread across the equator. The body of water that was believed to have been enclosed within the resulting crescent on the East side has been named the Tethys Sea. The vast ocean that once surrounded the supercontinent of Pangaea has been named 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.

Sea levels in the Permian remained generally low, and near-shore environments were limited by the collection of almost all major landmasses into the single continent Pangaea. 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.

Three general areas are especially noted for their Permian deposits: the Ural Mountains, 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 marine invertebrates are widely used to identify Permian strata and correlate 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 (four-legged vertebrates).

The dry conditions of the continental climate would have 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. The Permian began with the Carboniferous flora still flourishing. About the middle of the Permian, there was a major transition in vegetation. The swamp-adapted 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, apparently 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. Rich forests were present in many areas, with a diverse mix of plant groups.

The Permian period saw the development of a fully terrestrial fauna and the appearance of the first large herbivores and carnivores. Permian tetrapods (four-legged vertebrates) consisted of temnospondyli, lepospondyli, and batrachosaur amphibians and sauropsid and synapsid (pelycosaurs and therapsids) reptiles.

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 appearing at the end of the Permian were the first cynodonts, which are considered to have been ancestors to the mammals, which appeared during the Triassic. Another group of therapsids, the therocephalians (such as Trochosaurus), arose in the Middle Permian.

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

Permian-Triassic extinction event

The Permian ended with the most extensive extinction event recorded in paleontology—the Permian-Triassic extinction event. About 90 to 95 percent of marine species became extinct, as well as 70 percent of all terrestrial organisms. On an individual level, perhaps as many as 99.5 percent 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, became extinct before the end of the Permian.

In 2006, a group of American scientists from 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.

References
ISBN links support NWE through referral fees

  • Hoffmann, J. H. “When life nearly came to an end.” National Geographic 198(3):100-­113, 2000.
  • Kump, L. R., A. Pavlov, and M. A. Arthur. “Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia.” Geology 33:397-400, 2005.
  • Ogg, J. Overview of global boundary stratotype sections and points (GSSP's) International Commission on Stratigraphy (ICS), 2004. Retrieved September 24, 2007.

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