How to kill (almost) all life: the end-Permian extinction event

The biggest mass extinction of the past 600 million years (My), the end-Permian event (251 My ago), witnessed the loss of as much as 95% of all species on Earth. Key questions for biologists concern what combination of environmental changes could possibly have had such a devastating effect, the scale and pattern of species loss, and the nature of the recovery. New studies on dating the event, contemporary volcanic activity, and the anatomy of the environmental crisis have changed our perspectives dramatically in the past five years. Evidence on causation is equivocal, with support for either an asteroid impact or mass volcanism, but the latter seems most probable. The extinction model involves global warming by 6degreesC and huge input of light carbon into the ocean-atmosphere system from the eruptions, but especially from gas hydrates, leading to an ever-worsening positive-feed back loop, the 'runaway greenhouse'.