Volcanic CO2 degassing postdates thermogenic carbon emission during the end-Permian mass extinction

Massive carbon dioxide (CO2) emissions are widely assumed to be the driver of the end-Permian mass extinction (EPME). However, the rate of and total CO2 released, and whether the source changes with time, remain poorly understood, leaving a key question surrounding the trigger for the EPME unanswered. Here, we assimilate re-constructions of atmospheric PCO2 and carbonate & delta;13C in an Earth system model to unravel the history of carbon emissions and sources across the EPME. We infer a transition from a CO2 source with a thermogenic carbon iso-topic signature associated with a slower emission rate to a heavier, more mantle-dominated volcanic source with an increased rate of emissions. This implies that the CO2 degassing style changed as the Siberian Traps emplace-ment evolved, which is consistent with geochemical proxy records. Carbon cycle feedbacks from terrestrial eco-system disturbances may have further amplified the warming and the severity of marine extinctions.