By Ashley Yeager
31 March 2014
(Science News) – About 252 million years ago an estimated 96 percent of all species were wiped from Earth, and now scientists have a new suspect in the killing — methane-belching microbes.
The archaea Methanosarcina got faster at making methane by acquiring a gene from another microbe and then reproducing quickly, fueled by nickel spewing from Siberian volcanoes. The extra methane would have made the oceans acidic and added sulfur compounds to the air, driving the extinction of life at sea and on land, a team of researchers suggests March 31 in the Proceedings of the National Academy of Sciences. An earlier report estimated that the die-off happened in less than 60,000 years.
ABSTRACT: The end-Permian extinction is associated with a mysterious disruption to Earth’s carbon cycle. Here we identify causal mechanisms via three observations. First, we show that geochemical signals indicate superexponential growth of the marine inorganic carbon reservoir, coincident with the extinction and consistent with the expansion of a new microbial metabolic pathway. Second, we show that the efficient acetoclastic pathway in Methanosarcina emerged at a time statistically indistinguishable from the extinction. Finally, we show that nickel concentrations in South China sediments increased sharply at the extinction, probably as a consequence of massive Siberian volcanism, enabling a methanogenic expansion by removal of nickel limitation. Collectively, these results are consistent with the instigation of Earth’s greatest mass extinction by a specific microbial innovation.
SIGNIFICANCE: The end-Permian extinction is the most severe biotic crisis in the fossil record. Its occurrence has been attributed to increased CO2 levels deriving from massive Siberian volcanism. However, such arguments have been difficult to justify quantitatively. We propose that the disruption of the carbon cycle resulted from the emergence of a new microbial metabolic pathway that enabled efficient conversion of marine organic carbon to methane. The methanogenic expansion was catalyzed by nickel associated with the volcanic event. We support this hypothesis with an analysis of carbon isotopic changes leading up to the extinction, phylogenetic analysis of methanogenic archaea, and measurements of nickel concentrations in South China sediments. Our results highlight the sensitivity of the Earth system to microbial evolution.