Yale scientists have linked a 66-million-year-old crater in Mexico’s Yucatán Peninsula to the last mass extinction, debunking a long-held theory that volcanoes instigated the extermination.

Researchers found that the asteroid that landed on Earth at the end of the Cretaceous caused rapid ocean acidification and disrupted Earth’s natural recovery system, in addition to killing off the dinosaurs. This finding provides the first independent chemical evidence to support paleontological data that marks this mass extinction.

“It doesn’t seem to be possible that there was a contributing cause from the volcanoes in causing extinction,” Michael Henehan, the study’s first author and a former Yale postdoctoral researcher, said.

Led by Pincelli Hull — who is the study’s senior author and assistant professor of geology and geophysics — the team found high extinction rates among aquatic organisms with calcium carbonate shells. Meanwhile, other shelled creatures in these ancient oceans survived fairly well throughout the mass extinction.

“The ocean acidification we observe could easily have been the trigger for mass extinction in the marine realm,” Hull told Yale News.

The study explained how the Earth recovered after the extinction. Normally, chemical weathering on land washes out calcium and bicarbonate ions to the oceans. Aquatic organisms with calcium carbonate shells use these ions to build their encasement and the process helps maintain a stable ocean chemistry. This process was disrupted by the extinction of the calcifying organisms, leading to an abnormally high rise in pH before it could return back to standard levels after thousands of years.

The scientists tested previous theories using an Earth system model to study the pathway of recovery that Earth took. Their explanation of the carbon cycle demonstrated how the ocean gradually recovered after the instantaneous extinction event.

First inspired as a child by dinosaur comics and curiosity about their mass extinction, Henehan said he now credits the applicability of his research to climate change as a driver for his interest in the topic.

“When trying to understand climate change, and what the impact of human anthropogenic carbon dioxide release will be, we have to think about how the Earth cycles carbon and how much carbon you can get away with releasing before you have big environmental and ecological damage,” he said.

Human activities have increased atmospheric carbon dioxide. Thomas said there is convincing evidence suggesting this has already caused ocean acidification. The prospect puts aquatic life in danger.

“Our evidence shows  that ocean acidification has had dire effects on corals in the past, suggesting that our prospects for the health of coral reefs are negative,” Thomas said. “Although this is research on things that happened millions of years ago, it has unfortunate relevance to the future of the world’s ecosystems.”

There has been a 30 percent increase in surface ocean water acidity since the start of the Industrial Revolution, according to the National Oceanic and Atmospheric Administration.

Katherine Du | katherine.du@yale.edu