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Dying dinosaurs
What led to the mass extinction that did in the dinosaurs more than 65 million years ago? Scientists say volcano-caused climate change was a contributing cause. (Credit: Zina Deretsky / NSF)

Scientists generally agree that a catastrophic asteroid blast killed off the dinosaurs and most of Earth’s other species more than 65 million years ago, but newly described evidence supports the view that there was an additional culprit: rapid climate change brought on by volcanic eruptions.

The idea that the Cretaceous-Paleogene mass extinction was a one-two punch isn’t new. For decades, scientists have debated how much the eruptions in the Indian subcontinent’s Deccan Traps contributed to the die-off, as opposed to the miles-wide space rock that hit the coast of Mexico’s Yucatan Peninsula.

A study of ancient Antarctic fossil seashells, published online today in Nature Communications, turns the spotlight on the volcanoes’ effect.

The shell specimens analyzed for the study covered a range of sizes, as shown in this photograph. A quarter is included to show the scale. (Credit: Sierra Petersen / University of Michigan)

The scientists behind the study sampled scores of bivalve fossils from Antarctica’s Seymour Island, and analyzed the distribution of clumped isotopes for various elements, including oxygen and carbon. They say their method produced a reliable chart of the ups and downs in temperature levels during a key period, stretching from 69 million to 65.5 million years ago.

The analysis showed that temperatures jumped by somewhere between 4.5 and 11.1 degrees Centigrade (8 to 20 degrees Fahrenheit) when the Deccan Traps were in full swing, a little more than 66 million years ago. Temperatures settled back down, then spiked upward again when the asteroid hit a few hundred thousand years later.

“This new temperature record provides a direct link between the volcanism and impact events and the extinction pulses — that link being climate change,” the study’s principal author, Sierra Petersen of the University of Michigan, said in a news release.

The combination of the two events delivered a “theoretical ‘one-two punch,'” she said. About 10 of the bivalve species found at Seymour Island went extinct during the earlier temperature spike, and the other 14 went extinct when the asteroid hit.

The Deccan Traps’ biggest eruptive period is thought to have lasted for tens of thousands of years, piling up lava to a depth of more than 6,500 feet over a broad area of west-central India. Volcanoes spewed out carbon dioxide as well as sulfur dioxide, other gases and particulates.

Petersen and her colleagues surmise that the CO2 emissions led to the spike in global warming, which faded as natural processes such as rock weathering scrubbed the CO2 from the air. The sulfur dioxide could have contributed to the cooling effect.

The asteroid strike apparently caused a similar up-and-down spike in temperatures, the researchers reported.

The researchers say the peak temperature that was reached during the spike in volcanic activity probably wouldn’t have been enough by itself to render species extinct, because many of those species survived temperatures that were just as warm earlier in Earth’s history.

“It is possible that the rate of warming, as opposed to the maximum temperatures reached, led to extinction,” they wrote. “The rate of warming during the Deccan temperature spike appears to be more rapid than at any other temperature change seen in the record.”

Does that mean rapid climate change is bad? If so, we’re in trouble.

In addition to Petersen, the authors of “End-Cretaceous Extinction in Antarctica Linked to Both Deccan Volcanism and Meteorite Impact via Climate Change” include Andrea Dutton and Kyger Lohmann.

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