Permian–Triassic extinction event instance of extinction event
The Permian–Triassic (P–T, P–Tr) extinction event, also known as the Late Permian extinction event, the Latest Permian extinction event, the End-Permian extinction event, and colloquially as the Great Dying, forms the boundary between the Permian and Triassic geologic periods, and with them the Paleozoic and Mesozoic eras respectively, approximately 251.9 million years ago. As the largest of the "Big Five" mass extinctions of the Phanerozoic, it is the Earth's most severe known extinction event, with the extinction of 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species. It is the largest known mass extinction of insects. There is evidence for one to three distinct pulses, or phases, of extinction.The scientific consensus is that the main cause of extinction was the large amount of carbon dioxide emitted by the flood basalt volcanic eruptions that created the Siberian Traps, which elevated global temperatures and acidified the oceans. Proposed contributing factors include: the emission of much additional carbon dioxide from the thermal decomposition of hydrocarbon deposits, including oil and coal, triggered by the eruptions; and emissions of methane by novel methanogenic microorganisms, perhaps nourished by minerals dispersed in the eruptions.The speed of recovery from the extinction is disputed. Some scientists estimate that it took 10 million years (until the Middle Triassic). due both to the severity of the extinction and because grim conditions returned periodically over the course of the Early Triassic, causing further extinction events, such as the Smithian-Spathian boundary extinction. However, studies in Bear Lake County, near Paris, Idaho, and nearby sites in Idaho and Nevada showed a relatively quick rebound in a localized Early Triassic marine ecosystem, taking around 3 million years to recover, while an unusually diverse and complex ichnobiota is known from Italy less than a million years after the end-Permian extinction. Additionally, the complex Guiyang biota found near Guiyang, China also indicates life thrived in some places just a million years after the mass extinction, as does a fossil assemblage known as the Shanggan fauna found in Shanggan, China and a gastropod fauna from the Al Jil Formation of Oman. Regional differences in the pace of biotic recovery suggest that the impact of the extinction may have been felt less severely in some areas than others, with differential environmental stress and instability. In addition, it has been proposed that although overall taxonomic diversity rebounded rapidly, functional ecological diversity took much longer to return to its pre-extinction levels; one study concluded that marine ecological recovery was still ongoing 50 million years after the extinction, during the latest Triassic, even though taxonomic diversity had rebounded in a tenth of that time.
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