There has been a lot of debate around what killed off the dinosaurs, but according to a study published in Science volcanic activity can be ruled out.
The researchers say that an asteroid impact caused the extinction, but volcanoes may have shaped the life that followed.
"Our evidence strongly suggests that volcanic activity does not contribute to the extinction," lead author Pincelli Hull, an assistant professor in geology and geophysics at Yale University, told Newsweek.
The asteroid impact was certainly big enough to cause the extinction event on its own, she added.
Hull's research adds more weight to the shifting consensus that an asteroid (not volcanic activity or a combination of the two) was responsible for the Cretaceous-Tertiary (or K-Pg) extinction event that wiped out the dinosaurs and ushered in the era of mammals.
"The extinction of the dinosaurs and much other life 66 million years ago is one of the great mysteries of science," Paul Pearson, Honorary Professor at Cardiff University's School of Earth and Ocean Sciences who was not involved in the study, told Newsweek.
Both are known to be of the right age," he said. "But which was to blame for the extinction? Or was it an unlucky double whammy?"
Few scientists dispute that the asteroid Chicxulub played a role in the extinction event that wiped out the dinosaurs 66 million years ago. However, some academics have argued that a series of eruptions in the Deccan traps in modern-day India played a secondary—or even a primary—role in the K-Pg extinction event, casting lava and toxic gases far and wide over a period of hundreds of thousands of years. This argument has split the academic field into two main camps.
"The feelings run high in science on the K-Pg extinction," Matt Genge, a senior lecturer in Earth and planetary science at Imperial College Lonon who was not involved in the study, told Newsweek. "It may sound funny but there are scientists who will hardly talk to each other in the corridor because they are on different sides of the debate."
Hull and colleagues looked for signatures of the Deccan volcanism in a bid to determine "once and for all" if they played a role, co-author Paul Brown, a professor of picropalaeontology at University College London, told Newsweek.
Their case rests on the timing of the volcanic eruptions, specifically the timing of the gas it released (known as outgassing), which the study's authors say took place too early to have triggered the extinction.
Hull, Brown and colleagues examined geological records of warming and carbon cycle change, comparing the data to models of volcanic warming to find a best-fit scenario. Carbon can be measured from the shells of plankton and shellfish, which are formed from carbonate extracted from CO2 in the oceans.
They found the most likely scenario was a period of volcanic warming 200 thousand years before extinction took place—a period when, according to previous studies, dinosaurs should have been thriving.
But while the volcanic eruptions do not appear to have caused disruption on the scale previously suggested, the activity did cause some havoc and displaced several species, researchers say.
"Volcanic activity in the late Cretaceous caused a gradual global warming event of about two degrees, but not mass extinction," Michael Henehan, a former Yale researcher who compiled temperature records for the paper, said in a statement.
It also may have helped shape life that emerged from the ashes, the study authors say.
"We, therefore, conclude that impact and extinction created the initial opportunity for the rise of Cenozoic species and communities"—a group that includes saber-tooth cats, cave bears and woolly mammoths—"but Deccan volcanism might have contributed to shaping them during the extinction aftermath," they wrote.
"Over 90 percent of nannoplankton species disappeared at the K-Pg event," said Brown. "So understanding what drove that extinction helps us understand how the ocean may respond to other drivers of environmental change, such as current global warming and ocean acidification.
The extinction event may have occurred in the distant past but researchers say it has major significance for us today.
"This is an intriguing glimpse into a momentous event in Earth's history. If it hadn't happened then we most likely wouldn't be here, and perhaps the intelligent species on Earth would have have been saurian," said Genge.
While the odds of another Chicxulub occurring any time soon is slim—we have already mapped any asteroids larger than one kilometer (0.6 miles) with none posing an imminent threat—there is a warning to be had.
"This research is a cautionary tale," said Genge. "We have caused as much damage to our planet in 200 years as some of the largest volcanic eruptions caused in 100,000 years."
"In the late Cretaceous the little sea creatures heroically defeated the volcanoes, today the ecosystem is being overwhelmed by the pace of change caused by the most destructive force on Earth—us."
