This eruption was the second-largest in the 20th century, but it pales in comparison to the Deccan eruptions that occurred for thousands of years at the end of the Cretaceous period, approximately 65 million years ago, in what is now India. Researchers don’t know exactly how these massive eruptions affected the climate back then, but they figure the impact was pretty intense.

In fact, this type of massive volcanism may have been involved in the mass extinction that took place at the end of the Cretaceous, in which the dinosaurs and many other organisms disappeared. (The other possibility is an impact from an extraterrestrial object.)

In order to begin investigating what kind of environmental impact the Deccan volcanism would have had, Stephen Self of Open University in the United Kingdom and his colleagues analyzed the chemistry of certain crystals in the lava rocks left over from the eruptions.

Their results suggested that the Deccan eruptions released vast amounts of sulfur and maybe other gasses like chlorine into the atmosphere – amounts large enough to have some pretty significant effects on climate. For example, the eruptions may have spewed about 10 times as much sulfur into the atmosphere as human activities have in the last two centuries. -American Association for the Advancement of Science