New research by a Princeton University scientist contradicts the long-standing theory of what caused dinosaur extinction more than 65 million years ago.

Princeton professor Gerta Keller and colleagues have released research in recent months dispelling the theory that a meteor impact off the coast of Mexico — called the Chicxulub crater — as the main cause of the dinosaur extinction. Keller places that impact 300,000 years before dinosaurs ultimately became extinct.

Most of Keller’s research points to an increased period of volcanic activity and subsequent global warming as a probable cause of dinosaurs’ extinction. The possibility of another meteor impact causing the extinction isn’t ruled out, though.

Christopher Brochu, assistant professor of geoscience at the University of Iowa, said Keller’s work will raise serious doubts and make scientists question the effects of asteroids.

“We have other craters on Earth that are not correlated with any mass extinction,” he said. “[Scientists] will have to be more careful in describing the effects of asteroid impacts.”

He said many elements that occurred over a long period of time are the most likely cause of the dinosaur extinction, rather than a single instantaneous incident, such as an impact.

Jonathan Adrain, assistant professor of geoscience with a specialty in invertebrate paleontology at the University of Iowa, said Keller’s findings are not surprising to many in the scientific community.

“I would say there’s a fairly strong resistance among paleontologists in believing it happened as quickly as an impact,” he said. “Most think it happened over time.”

He said the Chixculub impact has always been questioned by scientists because some evidence found at the site does not make sense. One example is the discovery of burrows, suggesting there were animals at the crater not long after the supposed mass extinction.

Another reason for the questioning is that scientists have only focused on the extinction of dinosaurs without considering many other organisms that would have been affected by an asteroid impact, Brochu said.

“We need to gather as many elements from that time period [as possible],” he said. “There is no such thing as a mass extinction unless we know what is involved.”

A strong point of Keller’s research came from a new study of information found by drilling the core of the Chixculub impact. Keller was able to find a date for the impact by studying the levels of iridium and limestone in the crater.

“There is more there than we can understand right now,” said Bjorn Brooks, graduate student in geological and atmospheric sciences. “It’s easy to appeal to the instantaneous extinction theory when we don’t understand all the details.”

Brooks is studying metazoan life and the rate at which life evolves.

Keller’s research on volcanism and its effect on the environment is still relevant because it has the same cause-effect relationship we share with the environment.

“What geologists often find is that little things often accumulate into a snowball [effect],” he said. “A very small change can result in very profound effects.”

That is why studying the dinosaur extinction is essential today, Brooks said. Scientists want to know if the elements we put into our environment, such as pollution, may have catastrophic consequences in the future.

“If the whole dinosaur population could die out, we wonder if it could happen to us,” he said. “It’s important to know if the small changes we are making to the environment could lead to extinction.”

Keller’s research could also lead to renewed curiosity in the demise of the dinosaurs.

Since Keller’s findings lead some to think there was another impact that caused the extinction, Adrain said research into that would build interest in the scientific community to find another crater that could have caused the mass extinction.

“I think there’s going to be a lot of excitement in it, and a lot of money thrown into it,” he said.