:''Permian is also an alternative name for the
Permic languages. For the high school, see
Permian High School.''
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.
Subdivisions
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
:
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 --
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.
Paleogeography
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.
Climate
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.
Life
Anteosaurus in landscape - Middle Permian, South Africa
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.
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 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.
See also
★
List of fossil sites ''(with link directory)''
★
Permian tetrapods
Notes
1. http://www.historyfiles.co.uk/FeaturesAfrica/Permian_Extinction1.htm
References
★ Ogg, Jim; June, 2004, ''Overview of Global Boundary Stratotype Sections and Points (GSSP's)'' http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.
★
External links
★
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)
★
Examples of Permian Fossils
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