To: combjelly who wrote (778576 ) 4/6/2014 6:59:26 PM From: Bilow Read Replies (2) | Respond to Hi combjelly; Re: "You've got to be kidding. So you are a Permian-Triassic Extinction denier? ";Researchers have variously suggested that there were from one to three distinct pulses, or phases, of extinction. [6] [10] [11] [12] There are several proposed mechanisms for the extinctions; the earlier phase was probably 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 , coal/gas fires and explosions from the Siberian Traps , [13] and sudden release of methane clathrate from the sea floor; a runaway greenhouse effect triggered by methane -producing microbes, [14] gradual changes include sea-level change, anoxia , increasing aridity , and a shift in ocean circulation driven by climate change . However, the pattern of isotope shifts expected to result from a massive release of methane does not match the patterns seen throughout the early Triassic . Not only would a methane cause require the release of five times as much methane as postulated for the PETM, [15] but it would also have to be reburied at an unrealistically high rate to account for the rapid increases in the 13C/12C ratio (episodes of high positive d13C) throughout the early Triassic, before being released again several times. [15] en.wikipedia.org
