Amassive asteroid impact is likely to blame for the extinction event that marks the end of the Cretaceous period, according to a study published today (January 17) in Science.
Researchers led by Pincelli Hull of Yale University used deep-sea sediment cores extracted from the North Atlantic to investigate ocean carbon cycling and temperature shifts during the widespread disappearance of species around 66 million years ago, the cause of which is the subject of hot debate.
Some researchers argue that volcanic gases in India’s Deccan Traps were the main driver of the extinctions, while others propose that the impact of a giant asteroid, 10 km in diameter, in Mexico’s Yucatan Peninsula was the most probable cause.
“A lot of people have wanted to argue that both the impact and the volcanism mattered in the extinction,” says Hull to The New York Times. “And what we’re seeing is, it doesn’t look like it. It’s just the impact.”
In mapping a timeline of global temperature shifts and exploring different scenarios for when the Deccan eruptions may have occurred, Hull and her team discovered that temperatures did not spike around the time of the extinction event, as the volcanic hypothesis posits. Instead, the most likely scenario is that the eruptions occurred primarily before the asteroid struck Earth.
“We found support for major outgassing beginning and ending distinctly before the impact [of the asteroid], with only the impact coinciding with mass extinction and biologically amplified carbon cycle change,” the authors conclude in the paper.
If some eruptions took place after the mass extinction, their effects were dampened by carbon absorption by the oceans, the team concluded. That’s because plankton that made their shells out of calcium carbonate were among the countless organisms wiped out. “Without those calcifiers to draw acid-buffering calcium carbonate out of the seawater, the oceans may have absorbed large amounts of acidic carbon dioxide gas emitted by the Deccan Traps in the immediate aftermath of the extinction,” according to Science News. “That absorption could have muted a temperature effect of the volcanic emissions.”
“I’m sure the debate will rage on, because there are entrenched voices on either side,” vertebrate paleontologist Stephen Brusatte of the University of Edinburgh tells The New York Times. “But it’s getting harder and harder to fathom that the asteroid was innocent.”
Amy Schleunes is an intern at The Scientist. Email her at email@example.com.