The end-Permian mass extinction: a still unexplained catastrophe

The end-Permian mass extinction is widely regarded as the largest mass extinction in the past 542 million years with loss of about 95% of marine species and 75% of terrestrial species. There has been much focus and speculation on what could have caused such a catastrophe. Despite decades of study the cause or causes remain mysterious. Numerous scenarios have been proposed, including asteroid impact, Siberian flood basalt volcanism, marine anoxia...