Did volcanoes contribute to the demise of the dinosaurs?

Nearly 66 million years ago, a mass extinction event wiped out the dinosaurs and most life on Earth at the end of the Cretaceous period. When an impact crater and other evidence of an ancient asteroid strike were discovered in the 1980s and 1990s, researchers believed that an asteroid caused the mass extinction.

But skepticism has emerged in the scientific community, as many extinction events also occur in tandem with volcanic eruption.

Was the mass extinction triggered by the asteroid, was it a series of volcanic eruptions over thousands of years, or did the combined power cause this event?

Two teams of researchers looked to India’s Deccan Traps, one of the largest volcanic features on Earth. Their differing findings were published in separate papers in the journal Science on Thursday.

Studying the Deccan Traps would allow the researchers to determine an eruption timeline and compare it to the Chicxulub asteroid impact on Mexico’s Yucatan Peninsula, half a world away from the Deccan Traps flood basalts.

Some of the Deccan Traps are more than a mile thick in some areas. The eruptions that formed the Deccan Traps took place over the course of a million years, sending lava flows in directions more than 300 miles away.

Blair Schoene, associate professor of geosciences at Princeton University’s Environmental Institute, and his team studied the feature using uranium-lead dating on crystals of zircon, which is found in cooling magma. The uranium isotopes start decaying as zircon crystallizes, transforming into lead isotopes at a steady rate. So Schoene and his team took samples from nine Deccan formations, like ash beds and the soil between ancient lava flows.

Their timeline suggests that the Deccan Traps erupted in four 100,000-year events, each releasing a significant amount of greenhouse gases and magma.

Volcanic eruption is also thought to be a driver of climate change because so many greenhouse gases are released by eruptions and even the cooling of lava as it settles over other rocks.

The timeline also suggests that the eruptions began before the asteroid impact, which implies that the climate change caused by eruptions could have triggered mass extinction ahead of the collision.

A limitation of this kind of dating is that the crystals may have formed before eruption, which could affect the timeline.

A second research team, University of Liverpool geoscientist Courtney Sprain and her colleagues, used argon-argon dating. This technique measures the argon gas released from a sample after nuclear radiation. It’s less precise than uranium-lead dating but directly measures the age of the lava flow.

Sprain’s team found that over 75% of the Deccan lava erupted about 600,000 years after the extinction event. This led them to believe that the asteroid may have caused an increase in eruptions. They also suggest that the eruptions would have caused delayed recovery of the biosphere after the asteroid impact.

“Now that we have dated Deccan Traps lava flows in more and different locations, we see that the transition seems to be the same everywhere,” said Paul Renne, senior author of the second study and University of California-Berkeley professor-in-residence of Earth and planetary science, said in a statement. “I would say, with pretty high confidence, that the eruptions occurred within 50,000 years, and maybe 30,000 years, of the impact, which means they were synchronous within the margin of error.”

Both dating methods provide different ways of looking at the Deccan Traps eruptions, and they’re more precise than previous dating methods.

The studies agree that the Deccan Traps eruptions occurred over the course of a million years, beginning about 400,000 years before the mass extinction and continuing for about 500,000 years after. And both agree that the Deccan Traps probably played a part in the extinction event.

Looking ahead, the researchers agreed that they should collaborate. These new datasets create more questions, especially as we look to our future.

There have been five mass extinction events on Earth, and scientists believe that we’re living through the sixth — and that we’re at fault for this one.

“Understanding past extinctions events — their causes, and eventual climatic and biotic recoveries — is crucial therefore when trying to wrap our heads around the many possible outcomes of our current trajectory towards disastrous climate change, ecosystem destruction, and potential mass extinction,” Schoene said.

“This is particularly true for the Cretaceous-Paleogene mass extinction event as the Chicxulub impact is one of the few events in Earth’s history that occurred on a timescale similar to or potentially faster than modern climate change,” Sprain said.