Big asteroid may not have killed dinosaurs

PRINCETON, N.J., March 2 (UPI) -- European and U.S. scientists are questioning the notion that a vast Mexican crater is the scar left by an asteroid that wiped out Earth's dinosaurs.

Most science textbooks teach that 65 million years ago parts of a giant asteroid formed what is called the Chicxulub crater on the Yucatan Peninsula.

The consensus is that fast-moving debris from the asteroid's impact would have superheated the atmosphere so that forests and vegetation around the world burst into flames.

And that, in turn, blackened the atmosphere, chilling the temperature and killing cold-blooded animals like dinosaurs.

But now European and U.S. scientists question that belief, the Daily Telegraph reported.

In a study published Tuesday in the Proceedings of the National Academy of Sciences, Gerta Keller of Princeton University and her colleagues suggest the Chicxulub crater predates the mass extinction by 300,000 years.

Their conclusion came after they studied strata in a core drilled from the crater.

The team suggests a more complex series of events such as an additional asteroid impact, perhaps in the Shiva Crater in India, volcanism, and climate change.