PROVIDENCE, R.I. -- All asteroid-based extinctions great and small are not alike.

A new study says the asteroid that struck Earth 65 million years ago and wiped out the dinosaurs was particularly deadly to North America because it hit the Yucatan peninsula from the southeast at a 20- to 30-degree angle, spreading the devastating impact of its energy northwest.

The oblique angle of the asteroid's contact with Earth coupled its impact energy with that of the atmosphere and planetary surface to send waves of ground-hugging, vaporous fireballs onward, the study says. This resulted in an extinction intensity most severe downrange of the impact in North America.

The study suggests one rationale for the dire consequences of such an impact: The severity of extinctions that result from an object's impact on Earth may reflect the incoming object's angle.

Editors: Color transparencies are available through the News Bureau.

"This finding may help us determine what other impacts did to Earth in the past and what they may do in the future," said Peter Schultz, professor of geological sciences at Brown University. Schultz and Steven D'Hondt, professor of oceanography at the University of Rhode Island, are co-authors of the study in the November issue of the journal Geology.

The researchers suggest that the relatively low angle of the Yucatan impact propelled a ballistic fireball downrange into North America. The fireball carried a two-mile-deep layer of vaporized rock and other material sheared off the Yucatan. The killing zone of matter cascaded through the atmosphere at near orbital speed, across North America and eventually around the globe.

"It was like a nuclear explosion taken north on a jet-powered sleigh ride," Schultz said. "This was indeed the day the Earth shook."

As evidence, the researchers show that the horseshoe-shaped Yucatan crater match
'"/>

Contact: Scott Turner
Scott_Turner@Brown.edu
401-863-2476
Brown University
30-Oct-1996