<P> The Permian--Triassic (P--Tr or P--T) extinction event, colloquially known as the Great Dying, the End - Permian Extinction or the Great Permian Extinction, occurred about 252 Ma (million years) ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras . It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct . It is the only known mass extinction of insects . Some 57% of all families and 83% of all genera became extinct . Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event, possibly up to 10 million years . Studies in Bear Lake County near Paris, Idaho showed a quick and dynamic rebound in a marine ecosystem, illustrating the remarkable resilience of life . </P> <P> There is evidence for one to three distinct pulses, or phases, of extinction . Suggested mechanisms for the latter include one or more large meteor impact events, massive volcanism such as that of the Siberian Traps, and the ensuing coal or gas fires and explosions, and a runaway greenhouse effect triggered by sudden release of methane from the sea floor due to methane clathrate dissociation according to the clathrate gun hypothesis or methane - producing microbes known as methanogens . Possible contributing gradual changes include sea - level change, increasing anoxia, increasing aridity, and a shift in ocean circulation driven by climate change . </P> <P> Until 2000, it was thought that rock sequences spanning the Permian--Triassic boundary were too few and contained too many gaps for scientists to reliably determine its details . However, it is now possible to date the extinction with millennial precision . U--Pb zircon dates from five volcanic ash beds from the Global Stratotype Section and Point for the Permian--Triassic boundary at Meishan, China, establish a high - resolution age model for the extinction--allowing exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales . The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Ma, a duration of 60 ± 48 ka . A large (approximately 0.9%), abrupt global decrease in the ratio of the stable isotope C to that of C, coincides with this extinction, and is sometimes used to identify the Permian--Triassic boundary in rocks that are unsuitable for radiometric dating . Further evidence for environmental change around the P--Tr boundary suggests an 8 ° C (14 ° F) rise in temperature, and an increase in CO levels by 6997200000000000000 ♠ 2000 ppm (for comparison, the concentration immediately before the industrial revolution was 6996279999999999999 ♠ 280 ppm .) There is also evidence of increased ultraviolet radiation reaching the earth, causing the mutation of plant spores . </P>

What was the cause of the permian mass extinction
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