A U.S. geosciences professor says dinosaurs died gradually from climate change caused by volcanic eruptions in India and not because of a meteor strike.

Gerta Keller of Princeton University admits her theory contradicts the long-held hypothesis that dinosaurs died due to climate change after a giant meteor hit the Yucatan region of Mexico.

Keller bases her theory on her National Science Foundation-funded field work in India and Mexico that uncovered geologic evidence that the mass extinction and the meteor impact occurred at different times.

"The Chicxulub impact hit the Yucatan about 300,000 years before the mass extinction that included the dinosaurs and, therefore, could not have caused it," Keller said.

Keller and her team instead found the mass extinction coincided with the end of the main phase of India's Deccan eruptions, suggesting volcanism killed the dinosaurs.

Keller and her colleagues will present their findings during the December 2009 American Geophysical Union meeting in San Francisco. The work will also be included in an upcoming History Channel feature "What Really Killed the Dinosaurs."