Permian

The Permian is a period of the geologic time scale that extends from about 299.0 ± 0.8 Ma (million years before the present) to 251.0 ± 0.4 Ma (ICS 2004). It is the last period of the Paleozoic era and is followed by the Triassic period of the Cenozoic era.

At the end of the Permian, forming the boundary between the Permian and the Triassic, there was a mass extinction event called the Permian-Triasic extinction event (P-T or PT). Sometimes informally called the Great Dying, this was the Earth's most severe extinction event, with about 90 percent of all marine species and 70 percent of terrestrial vertebrate species going extinct.

Phanerozoic eon (542 mya - present)
Paleozoic era	Mesozoic era	Cenozoic era

Subdivisions

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)

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

Paleogeography

Map of Pangaea

During the Permian, all the Earth's major land masses, except portions of East Asia, were collected into a single supercontinent known as Pangaea. Pangaea 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.

As the Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, the Paleo-Tethys shrunk. A new ocean grew on its southern end, the Tethys Ocean, an ocean that would 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.

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 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.

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, 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 (true flies).

Permian tetrapods consisted of temnospondyli, lepospondyli, and batrachosaur amphibians and sauropsid 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 appearing 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.

See also

• Permian tetrapods

References

ISBN links support NWE through referral fees

• Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.
• Kump, L.R., A. Pavlov, and M.A. Arthur (2005). Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia. Geology 33 (May): 397-400. Digital object identifier (DOI): 10.1130/G21295.1.

• International Commission on Stratigraphy (ICS). 2005 (September 19). http://www.stratigraphy.org.

External links

Wikimedia Commons has media related to:

Permian

• University of California offers a more modern Permian stratigraphy
• Classic Permian strata in the Glass Mountains of the Permian Basin
• International Commission on Stratigraphy (ICS). Geologic Time Scale 2004. Retrieved September 19, 2005.

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