Volcanic activity did not play a direct role in the mass extinction event that killed the dinosaurs, an international team led by researchers at Yale University has found.

The study, published this week in the journal Science, showed that environmental impacts from massive volcanic eruptions in India, in a region known as the Deccan Traps, happened before the dinosaur extinction event 66 million years ago, and therefore did not contribute to the mass extinction.

Previous studies suggested that massive volcanic eruptions at the Deccan Traps may have contributed to the mass extinction event. 

"Volcanoes can drive mass extinctions because they release lots of gases, like SO2 and CO2, that can alter the climate and acidify the world," said Pincelli Hull, the study's lead author and an assistant professor at Yale. "But recent work has focused on the timing of lava eruption rather than gas release." 

They compared global temperature change and the carbon isotopes from marine fossils with models of the climatic effect of CO2 release. An isotope is an atom with a higher or lower number of neutrons than normal.

They concluded that most of the gas release happened well before the asteroid impact. The asteroid was the sole driver of extinction, according to the researchers.

Volcanic activity in the late Cretaceous period caused a gradual global warming event of about two degrees, but not mass extinction. After that, a number of species moved toward the North and South Poles but moved back well before the asteroid impact, according to the study.