New Doubts Raised Over What Killed Off Dinosaurs

Scientists investigating a vast crater off Mexico’s Yucatan peninsula are questioning a popular theory about dinosaurs, saying the collision that formed the crater happened too far back in time to have caused their extinction by itself.

Much evidence points to the idea that an asteroid or comet gouged the Earth about 65 million years ago, triggering volcanic and climate changes that eventually wiped out the dinosaurs.

“Since the early 1990s the Chicxulub crater on Yucatan, Mexico, has been hailed as the smoking gun that proves the hypothesis that an asteroid killed the dinosaurs and caused the mass extinction of many other organisms at the Cretaceous-Tertiary (K-T) boundary 65 million years ago,” the researchers write in the current issue of the Proceedings of the National Academy of Sciences.

But they said a core drilled out of the middle of the crater suggests it dates back more than 300,000 years before the K-T boundary and “thus did not cause the end-Cretaceous mass extinction as commonly believed.”

This finding would support an alternative theory that the dinosaurs and other forms of life were wiped out in a series of disasters that changed the Earth’s climate, according to the team led by Gerta Keller of Princeton University.

A contributing factor could be the busy period of volcanic activity known as Deccan volcanism. The name Deccan comes from an area of what is now India where a massive amount of molten material surged up from near the Earth’s core 65 million years ago.