PERMIAN EXTICION: THE GREAT DYING

The Permian extinction event, informally known as the Great Dying, was an extinction event that occurred 251.4 Ma (million years ago), forming the boundary between the Permian and Triassic geologic periods. It was the Earth's most severe extinction event, with up to 96% of all marine speciesand 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 were killed. Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after other extinction events.This event has been described as the "mother of all mass extinctions."Researchers have variously suggested that there were from one to three distinct pulses, or phases, of extinction.There are several proposed mechanisms for the extinctions; the earlier phase was likely due to gradual environmental change, while the latter phase has been argued to be due to a catastrophic event. Suggested mechanisms for the latter include large or multiple bolide impact events, increased volcanism, and sudden release of methane clathrate from the sea floor; gradual changes include sea-level change, anoxia, increasing aridity, and a shift in ocean circulation driven by climate change.There are several proposed mechanisms for the extinction event, including both catastrophic and gradualistic processes (similar to those theorized for the Cretaceous–Tertiary extinction event). The former include large or multiple bolide impact events, increased volcanism, or sudden release of methane hydrates from the sea floor. The latter include sea-level change,anoxia, and increasing aridity. Any hypothesis about the cause must explain the selectivity of the event, which primarily affected organisms with calcium carbonate skeletons; the long (4–6 million year) period before recovery started; and the minimal extent of biological mineralization (despite inorganic carbonates being deposited) once the recovery began.