Methanogenic Blow-up in the End-Permian Carbon Cycle

The cause of the end-Permian extinction---arguably Earth's greatest biological crisis, about 252 million years ago---remains mysterious. We focus on concurrent disruptions in the global carbon cycle. By transforming geochemical signals into physical fluxes, we reveal an incipient singularity in the flux of CO2 into the oceans. Given reports of pre-existing anoxia, we hypothesize that the anaerobic degradation of abundant recalcitrant organic carbon provided the CO2 source, and that the evolution of a new microbial metabolic pathway caused the blow-up. We show that the most probable date for the emergence of the fast acetoclastic pathway in Methanosarcina, responsible for most modern biogenic methane, ranges between 238-268 million years ago. Because methanogens are limited by nickel, we hypothesize that increased nickel concentrations enhanced Methanosarcina's growth. Our analyses of late-Permian South China sediments show that nickel indeed increased sharply at the extinction, probably as a consequence of concurrent Siberian volcanism.