Contact metamorphism, halocarbons, and environmental crises of the past

Abstract

Environmental context. What caused the biggest known mass extinction on Earth ~252 million years ago? A possible killer mechanism was the release of specific gases into the atmosphere, which eventually led to destruction of the ozone layer. This is now supported by new laboratory experiments in which ozone-destructing gases were generated when heating rocks from East Siberia (Russia) – reconstructing what happened naturally in Siberia during explosive gas eruptions 252 million years ago. Abstract. What triggered the largest know mass extinction at the Permian–Triassic boundary 252 million years ago, when 95% of the species in the oceans disappeared? New geological data suggest that eruptions of carbon (CH4, CO2) and halocarbon (CH3Cl and CH3Br) gases from the vast sedimentary basins of east Siberia could have triggered a period with global warming (5°–10°C) and terrestrial mass extinction. The gases were generated during contact metamorphism of sedimentary rocks around 1200°C hot igneous intrusions. One of the suggested end-Permian extinction mechanisms is the extreme ultraviolet radiation (UV-B) caused by a prolonged destruction of stratospheric ozone induced by the emitted halocarbons. This hypothesis is supported by a new set of experiments, where natural rock salt samples from Siberia were heated to 275°C. Among the gases generated during heating are methyl chloride (CH3Cl) and methyl bromide (CH3Br). These findings open up new possibilities for investigating ancient environmental crises.