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Of or belonging to the geologic time, system of rocks, or sedimentary deposits of the seventh and last period of the Paleozoic Era, characterized by the formation of the supercontinent Pangaea, the rise of conifers, and the diversification of reptiles and ending with the largest known mass extinction in the history of life.
n.The Permian Period.
[After Perm Oblast, a region of west-central Russia.]
The name applied to the last period of geologic time in the Paleozoic Era and to the corresponding system of rock formations that originated during that period. The Permian Period commenced approximately 290 million years ago and ceased about 250 million years ago. The system of rocks that originated during this interval of time is widely distributed on all the continents of the world. The Permian Period was a time of variable and changing climates, and during much of this time latitudinal climatic belts were well developed. During the latter half of Permian time, many long-established lineages of marine invertebrates became extinct and were not immediately replaced by new fossil-forming lineages. Rocks of Permian age contain many resources, including petroleum, coal, salts, and metallic ores. See also Living fossils.
During the Permian Period, several important changes took place in the paleogeography of the world. The joining of Gondwana to western Laurasia, which had started during the Carboniferous, was completed during Wolfcampian time (earliest Permian). The addition of eastern Laurasia (Angara) to the eastern edge of western Laurasia finished during Artinskian time (middle to latest early Permian) and completed the assembly of the supercontinent Pangaea. The climatic effects of these changes were dramatic. Instead of having a circumequatorial tropical ocean, such as during the middle Paleozoic, a large landmass with several high chains of mountains extended from the South Pole across the southern temperate, the tropical, and into the north temperate climatic belts. One very large world ocean, Panthalassa and its western tropical branch, the Tethys, occupied the remaining 75% of the Earth's surface, with a few much smaller cratonic blocks, island arcs, and atolls. See also Continental drift; Continents, evolution of; Paleogeography.
Most marine invertebrates of the Early Permian were continuations of well-established phylogenetic lines of middle and late Carboniferous ancestry. During early Permian time, these faunas were dominated by brachiopods, bryozoans, conodonts, corals, fusulinaceans, and ammonoids. The Siberian traps, an extensive outflow of very late Permian basalts and other basic igneous rocks (dated at about 250 million years ago), are considered by many geologists as contributing to climatic stress that resulted in major extinctions of many animal groups, particularly the shallow-water marine invertebrates. The end of the Permian is also associated with unusually sharp excursions in values of the carbon-12 isotope (12C) in organic material trapped in marine sediments, suggesting major disruption of the ocean chemistry system.
Terrestrial faunas included insects which showed great advances over those of the Carboniferous Coal Measures. Several modern orders emerged, among them the Mecoptera, Odonata, Hemiptera, Trichoptera, Hymenoptera, and Coleoptera. See also Insecta.
Of the vertebrates, labyrinthodont amphibians were common and varied; however, reptiles showed the greatest evolutionary radiation and the most significant advances. Reptiles are found in abundance in the lower half of the system in Texas and throughout most of the upper part of the system in Russia and also are common in Gondwana sediments. Of the several Permian reptilian orders, the most significant was the Theriodonta. These reptiles carried their bodies off the ground and walked or ran like mammals. Unlike most reptiles, their teeth were varied—incisors, canines, and jaw teeth as in the mammals—and all the elements of the lower jaw except the mandibles showed progressive reduction. Most of the known theriodonts are from South Africa and Russia. See also Paleozoic; Reptilia.
The latest period of Palaeozoic time, stretching approximately from 280 to 225 million years bp.
The noun has one meaning:
Meaning #1:
from 230 million to 280 million years ago; reptiles
Synonym: Permian period
The Permian is a geologic period that extends from about 299.0 ± 0.8 Ma to 251.0 ± 0.4 Ma (million years before the present; ICS 2004). It is the last period of the Paleozoic Era.
The three primary subdivisions 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. Epoch and age refer to time, and equivalents series and stage refer to the rocks.
Lopingian Epoch
Guadalupian Epoch
Cisuralian Epoch
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 -- Pangaea. One continent, even a very large one, has a smaller shoreline than six to eight smaller ones with the same total area. 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.
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. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink. A new ocean was growing 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 Pangaea. 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.
As the Permian opened, the Earth was still in the grip of an ice age, so the polar regions were covered with deep layers of ice. Glaciers continued to cover much of Gondwanaland, as they had during the late Carboniferous . At the same time the tropics were covered in swampy forests.
Towards the middle of the period the climate became warmer and milder, the glaciers receded, and the continental interiors became drier. Much of the interior of Pangaea was probably arid, with great seasonal fluctuations (wet and dry seasons), because of the lack of the moderating effect of nearby bodies of water. This drying tendency continued through to the late Permian, along with alternating warming and cooling periods.
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) amniotes. 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.
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 land organisms. On an individual level, perhaps as many as 99.5% of separate organisms died as a result of the event.[1]
There is also significant evidence that massive flood basalt eruptions from magma output lasting thousands of years in what is now the Siberian Traps contributed to environmental stress leading to mass extinction. The reduced coastal habitat and highly increased aridity probably also contributed. Based on the amount of lava estimated to have been produced during this period, the worst case scenario is an expulsion of enough carbon dioxide from the eruptions to raise world temperatures five degrees Celsius, not enough to kill off 95% of life.
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 gases in the atmosphere would destroy the toxic gas, but the hydrogen sulfide would soon consume all of the atmospheric gas available to change 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.
Another hypothesis builds on the flood basalt eruption theory. Five degrees Celsius would not be enough increase in world temperatures to explain the death of 95% of life. But such warming could slowly raise ocean temperatures until frozen methane reservoirs below the ocean floor near coastlines (a current target for a new energy source) melted, expelling enough methane, among the most potent greenhouse gases, into the atmosphere to raise world temperatures an additional five degrees Celsius. For perspective, a 10-degree increase today would turn southern England into the Sahara Desert. The frozen methane hypothesis helps explain the increase in carbon-12 levels midway into the Permian-Triassic boundary layer. It also helps explain why the first phase of the layer's extinctions was land-based, the second was marine-based (and starting right after the increase in C-12 levels), and the third land-based again.
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. Levels of iridium and quartz fracturing in the Permian-Triassic layer do not approach those of the Cretaceous-Tertiary boundary layer. Given that a far greater proportion of species and individual organisms became extinct during the former, doubt is cast on the significance of a meteor impact in creating the latter. Further doubt has been cast on this theory based on fossils in Greenland showing the extinction to have been gradual, lasting about eighty thousand years, with three distinct phases.
Many scientists believe that the Permian-Triassic extinction event was caused by a combination of some or all of the hypotheses above and other factors; the formation of Pangaea decreased the number of coastal habitats and may have contributed to the extinction of many clades.
| Permian period | ||
|---|---|---|
| Cisuralian | Guadalupian | Lopingian |
| Asselian |
Sakmarian Artinskian | Kungurian |
Roadian |
Wordian Capitanian |
Wuchiapingian Changhsingian |
| Paleozoic era | |||||
|---|---|---|---|---|---|
| Cambrian | Ordovician | Silurian | Devonian | Carboniferous | Permian |
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