What are some hypotheses to explain the Permo-Triassic mass extinction? (when 95% of marine invertebrates and 77% of land species became extinct)

A mass extinction is a large decrease in the number of species over a relatively short period of time (several millions of years). The most likely cause of this species decline is the formation of the supercontinent Pangaea. Its establishment meant fewer continental shelves for shallow marine dwellers, rabid fluctuations in climate/river input and widespread glaciations in the southern hemisphere that lead to sea regression.Another major cause was widespread volcanic activity (the Siberian Traps) as a result of a large mantle plume. The poisonous gases not only killed life in close proximity, but also lowered global temperatures by blocking heat from the sun. After this cooling period, the emission of greenhouse gases such as CO₂ increased the temperature again. Greenhouse gases were also increased because methane hydrates (methane ice) were released once temperatures became high enough to disrupt their stability (around 18 degrees).