Scientists have been trying to figure out what killed off the dinosaurs for decades. Most agree the asteroid or comet that struck the Yucatan Peninsula some 66 million years ago, the Chicxulub meteorite, played a significant role in snuffing them out, but the significance of the Deccan Traps eruptions has puzzled scientists.

Now, new research -- published Monday in the journal Nature Communications -- suggests the volcanic activity had a significant impact on Earth's climate, and perhaps, on the dinosaurs, too.

Researchers performed a global survey of ancient marine mollusk shells, revealing the chemical signatures of mercury contamination and ocean warming. The signatures match the timing of the Deccan Traps eruptions.

Scientists compared the ancient shells with freshwater clam shells collected near a mercury contamination site in Virginia's Shenandoah Valley. The chemical signatures matched.

"For the first time, we can provide insights into the distinct climatic and environmental impacts of Deccan Traps volcanism by analyzing a single material," lead study author Kyle Meyer, researcher at the University of Michigan, said in a news release. "It was incredibly surprising to see that the exact same samples where marine temperatures showed an abrupt warming signal also exhibited the highest mercury concentrations, and that these concentrations were of similar magnitude to a site of significant modern industrial mercury contamination."

Mercury is produced naturally, but it's also a byproduct of many industrial processes, including mining and coal power production. Coal plants in Virginia are responsible for the mercury contamination in Virginia's South River, where residents are warned not to drink the water or eat the river's fish.

"The modern site has a fishing ban for humans because of high mercury levels. So, imagine the environmental impact of having this level of mercury contamination globally for tens to hundreds of thousands of years," said Michigan geochemist Sierra Petersen.

Meyer led the marine mollusk survey as part of his doctoral work at Michigan. Petersen served as his advisor.

Previous studies have linked the Chicxulub meteorite with a bout of global volcanic activity, including the eruption of India's Deccan Traps.

Now, researchers have found evidence that the volcanic activity resulted in rising global temperatures and mercury levels.

Scientists have previously found evidence of mercury contamination in ancient sediment layers, but struggled to link the contamination with climate change. The fossil survey allowed researchers to locate evidence of the two phenomena in the same place -- fossilized biomineral remains.

"Mercury anomalies had been documented in sediments but never before in shells. Having the ability to reconstruct both climate and a volcanism indicator in the exact same materials helps us circumvent lots of problems related to relative dating," said Petersen. "So, one of the big firsts in this study is the technical proof of concept."

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