What Killed Dinosaurs and Other Life on Earth?

On the other hand, the researchers say, the theories in favor of annihilation by asteroid impact hinge upon the Chicxulub impactor, a space rock that crash-landed into Mexico’s Yucatan Peninsula around the same time that the dinosaurs went extinct.

“All other theories that attempted to explain what killed the dinosaurs got steamrolled when the crater the asteroid had gouged out was discovered,” says Keller. But there’s very little evidence of similar impact events that coincide with the other mass extinctions despite decades of exploration, he points out.

For his Senior Fellowship thesis, Green set out to find a way to quantify the apparent link between eruptions and extinctions and test whether the coincidence was just chance or whether there was evidence of a causal relationship between the two. Working with Keller and co-author Paul Renne, professor of Earth and planetary science at the University of California, Berkeley, Green turned to the supercomputers at the Dartmouth Discovery Cluster to crunch the numbers.

The researchers compared the best available estimates of flood basalt eruptions with periods of drastic species kill-off in the geological timescale, including but not limited to the five mass extinctions. To prove that the timing was more than a random chance, they examined whether the eruptions would line up just as well with a randomly generated pattern and repeated the exercise with 100 million such patterns. “Less than 1% of the simulated timelines agreed as well as the actual record of flood basalts and extinctions, suggesting the relationship is not just random chance,” says Green, who is now a graduate student at Princeton.

But is this proof enough that volcanic flood basalts sparked extinctions? If there were a causal link, scientists expect that larger eruptions would entail more severe extinctions, but such a correlation has not been observed until now.

By recasting how the severity of the eruptions is defined, the researchers make a convincing case to unequivocally incriminate volcanoes in their paper.

Rather than considering the absolute magnitude of eruptions, they ordered the events by the rate at which they spewed lava and found that the ones with the highest eruptive rates did indeed cause the most destruction.

“Our results make it hard to ignore the role of volcanism in extinction,” says Keller.

The researchers ran the numbers for asteroids too. The coincidence of impacts with periods of species turnover was significantly weaker, and only worsened when the Chicxulub impactor was not considered.

The eruption rate of the Deccan Traps in India suggests that the stage was set for widespread extinction even without the asteroid, says Green. The impact was the double whammy that loudly sounded the death knell for the dinosaurs, he adds.

Flood basalt eruptions aren’t common in the geologic record, says Green. The last one of comparable scale happened about 16 million years ago in the Pacific Northwest. But there are other sources of emissions that pose a threat in the present day, the researchers say.

“While the total amount of carbon dioxide being released into the atmosphere in modern climate change is still very much smaller than the amount emitted by a large igneous province, thankfully,” says Keller, “we’re emitting it very fast, which is reason to be concerned.”

Green says that this rate of carbon dioxide emissions places climate change in the framework of historical periods of environmental catastrophe.

Green describes Dartmouth’s Senior Fellowship program, which allows undergraduates to go beyond the curriculum in their senior year, as a unique opportunity to dive into a field of his choice and develop a taste for research.

“This work is a great example of what Senior Fellows can achieve,” says Keller.

Harini Barath is a freelance science writer. This article is published courtesy of Dartmouth College.