Then 252 million years ago, something happened to cause the greatest mass extinction in Earth’s history. Over a few hundreds of thousands of years, the catastrophe killed off more than 95 percent of life on Earth. Scientists call it the Great Dying. It cleared the way for the rise of the age of dinosaurs. Scientists have debated the Great Dying’s cause, although, in recent years, many have begun to settle on the idea that volcanic eruptions were the primary cause. And now a new study – based on the discovery of mercury buried in ancient rocks – provides the strongest evidence yet that volcanoes did cause the Great Dying. Paleontologists with the University of Cincinnati and the China University of Geosciences said they found a spike in mercury in the geologic record at nearly a dozen sites around the world, providing what they called “persuasive evidence” that volcanic eruptions were to blame for this global cataclysm.
The idea is that volcanic eruptions ignited vast deposits of coal, releasing mercury vapor high into the atmosphere. Eventually, these scientists say, the mercury rained down into the marine sediments, and it’s the analysis of those ancient sediments today, now trapped in rock, that provides the basis for this new study.