Editing Permian (section)

== Permian–Triassic extinction event ==
{{Main|Permian–Triassic extinction event}}
[[File:Extinction Intensity.svg|thumb|right|The Permian–Triassic extinction event, labeled "End P" here, is the most significant extinction event in this plot for marine [[genus|genera]] which produce large numbers of [[fossil]]s]]
The Permian ended with the most extensive [[extinction event]] recorded in [[paleontology]]: the [[Permian–Triassic extinction event]]. 90 to 95% of marine species became [[Extinction|extinct]], as well as 70% of all land organisms. It is also the only known mass extinction of insects.<ref name="kgs.ku.edu"/><ref>{{cite web|url=http://geology.about.com/od/extinction/a/aa_permotrias.htm|title=The Great Permian-Triassic Extinction|author=Andrew Alden|work=About.com Education|access-date=2009-11-05|archive-date=2012-11-18|archive-url=https://web.archive.org/web/20121118205640/http://geology.about.com/od/extinction/a/aa_permotrias.htm|url-status=dead}}</ref> Recovery from the Permian–Triassic extinction event was protracted; on land, ecosystems took 30 million years to recover.<ref name="SahneyBenton2008RecoveryFromProfoundExtinction"/> [[Trilobite]]s, which had thrived since [[Cambrian]] times, finally became extinct before the end of the Permian. [[Nautiloids]], a subclass of cephalopods, surprisingly survived this occurrence.

There is evidence that [[magma]], in the form of [[flood basalt]], poured onto the Earth's surface in what is now called the [[Siberian Traps]], for thousands of years, contributing to the environmental stress that led 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 the release of enough carbon dioxide from the eruptions to raise world temperatures five degrees Celsius.<ref name="palaeos.com">[http://palaeos.com/paleozoic/permian/permian.htm Palaeos: Life Through Deep Time > The Permian Period] {{Webarchive|url=https://web.archive.org/web/20130629232721/http://palaeos.com/paleozoic/permian/permian.htm|date=2013-06-29}} Accessed 1 April 2013.</ref>

Another hypothesis involves ocean venting of [[hydrogen sulfide]] gas. Portions of the [[Deep sea|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 event|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. Hydrogen sulfide levels might have increased dramatically over a few hundred years. Models 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.<ref name=Kump>{{cite journal
 |last1        = Kump
 |first1       = L.R.
 |first2       = A.
 |last2        = Pavlov
 |first3       = M.A.
 |last3        = Arthur
 |title        = Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia
 |journal      = Geology
 |volume       = 33
 |issue        = May
 |year         = 2005
 |pages        = 397–400
 |doi          = 10.1130/G21295.1
 |bibcode      = 2005Geo....33..397K
 |s2cid        = 34821866
 }}</ref> [[Hydrogen sulfide#Life adapted to hydrogen sulfide|There are species]] that can metabolize hydrogen sulfide.

Another hypothesis builds on the flood basalt eruption theory. An increase in temperature of five degrees Celsius would not be enough to explain the death of 95% of life. But such warming could slowly raise ocean temperatures until [[Methane clathrate|frozen methane reservoirs]] below the ocean floor near coastlines melted, expelling enough methane (among the most potent [[greenhouse gas]]es) into the atmosphere to raise world temperatures an additional five degrees Celsius. The frozen methane hypothesis helps explain the increase in carbon-12 levels found midway in 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.<ref>{{cite journal|last1=Benton|first1=Michael J.|last2=Twitchett|first2=Richard J.|title=How to kill (almost) all life: the end-Permian extinction event|journal=Trends in Ecology and Evolution|date=7 July 2003|volume=18|issue=7|pages=358–365|doi=10.1016/S0169-5347(03)00093-4}}</ref>