Researchers say mercury buried in ancient rock provides the strongest evidence yet that volcanoes caused the biggest mass extinction in the history of the Earth 252 million years ago. The catastrophe killed off more than 95 percent of life on Earth over the course of hundreds of thousands of years.

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Researchers say mercury buried in ancient rock provides the strongest evidence yet that volcanoes caused the biggest mass extinction in the history of the Earth 252 million years ago. The catastrophe killed off more than 95 percent of life on Earth over the course of hundreds of thousands of years.