Of the five mass extinctions in the Earth's past, one stands above the rest in magnitude: the Permian-Trassic extinction, known as the Great Dying. It saw the disappearance of almost 60 percent of all families, and over 80 percent of all genera—in the ocean, that added up to about 96 percent of all species. The cause of this event, 250 million years in the past, is still a matter of debate.
The most likely culprit is the prolific volcanism of the Siberian Traps—the erupted basalt still covers about 2 million square kilometers—but other events may have also played a role. Evidence for a massive destabilization of methane hydrates on the seafloor (a phenomenon described as "The Big Burp"), ocean anoxia, and even contemporary asteroid impacts have all been found.
A couple recent papers in the journal Geology have brought some new information to the discussion, and may help make the picture just a little bit clearer.
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