The impact of an asteroid or comet is acknowledged as the principal cause of the mass extinction that killed off most dinosaurs and about three-quarters of the planet’s plant and animal species 66 million years ago.
But massive volcanic eruptions in India may also have contributed to the extinctions. Scientists have long debated the significance of the Deccan Traps eruptions, which began before the impact and lasted, on and off, for nearly a million years, punctuated by the impact event.
Now, a University of Michigan-led geochemical analysis of fossil marine mollusk shells from around the globe is providing new insights into both the climate response and environmental mercury contamination at the time of the Deccan Traps volcanism.
From the same shell specimens, the researchers found what appears to be a global signal of both abrupt ocean warming and distinctly elevated mercury concentrations. Volcanoes are the largest natural source of mercury entering the atmosphere.
The dual chemical fingerprints begin before the impact event and align with the onset of the Deccan Traps eruptions.
When the researchers compared the mercury levels from the ancient shells to concentrations in freshwater clam shells collected at a present-day site of industrial mercury pollution in Virginia’s Shenandoah Valley, the levels were roughly equivalent.
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