Volcanic eruptions in what is now India did not lead to the extinction of the dinosaurs about 65 million years ago, a new study suggests.
Scientists have long argued over the cause of the Cretaceous-Palaeogene extinction event, during which three-quarters of all plant and animal species, including the dinosaurs, went extinct.
Most researchers favour the idea that a catastrophic, sudden mechanism such as an asteroid hit triggered the mass die-off, while others say a gradual rise in carbon dioxide (CO2) emissions from volcanoes in what is now India may have been the cause.
The study demonstrates that Earth’s oceans are capable of absorbing large amounts of carbon dioxide – provided it is released gradually over an extremely long time.
“One way that has been suggested that volcanism could have caused extinction is by ocean acidification, where the ocean absorbs CO2 and becomes more acidic as a result, just as it is doing today with fossil fuel-derived CO2,” said Michael Henehan, a postdoctoral associate at Yale University in US.
“What we wanted to do was gather all the evidence that’s been collected from ocean sediments from this time and add a few new records of our own, and consider what evidence there is for ocean acidification at this time,” Henehan said.
Researchers analysed sediments from the deep sea, looking for signs of dissolution that would indicate more acidic oceans.
The researchers found that the onset of volcanism did cause a brief ocean acidification event. Critically, though, the pH drop caused by CO2 release was effectively neutralised well before the mass extinction event.
“Combining this with temperature observations that others have made about this time, we think there is a conclusive case that although Deccan volcanism caused a short-lived global warming event and some ocean acidification, the effects were cancelled out by natural carbon cycling processes long before the mass extinction that killed the dinosaurs,” Henehan said.
This is not to say that CO2 released by volcanoes did not prompt climate effects, the researchers said.
Rather, the gases were released over such a long timescale their effect could not have caused a sudden, species die-off.
The study also has implications for understanding modern climate change, the researchers noted.
It suggests restricting CO2 release to much slower and lower levels over thousands of years can allow the oceans to adapt and avoid the worst possible consequences of ocean acidification, researchers said.
“The direct effects of an asteroid impact, like massive tsunamis or widespread fires, would have lasted only for a relatively short time,” said Donald Penman, a postdoctoral associate at Yale University.
“However, the loss of ecologically important groups of organisms following impact caused changes to the global carbon cycle that took millions of years to recover,” said Penman.
The study was published in the journal Philosophical Transactions of the Royal Society B.