ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Sunday, November 10, 1996 TAG: 9611110054
SECTION: NATIONAL/INTERNATIONAL PAGE: A-4 EDITION: METRO
DATELINE: SAN FRANCISCO
SOURCE: KEAY DAVIDSON SAN FRANCISCO EXAMINER
AN ASTEROID CRASH in Mexico is blamed for incinerating much of the continent's flora and fauna and changing the world's climate.
The North American continent and many of its creatures were fried 65 million years ago in a nightmarish ``corridor of incineration'' - an immense, white-hot jet that gushed from an asteroid crash in Mexico, scientists say.
The conclusion, based partly on laboratory experiments at NASA's Ames Research Center in Mountain View, Calif., may solve an old puzzle: Why did the asteroid impact cause more extinctions in North America than anywhere else?
In recent years, most scientists have accepted the idea that a falling asteroid wiped out the dinosaurs and many other species 65 million years ago. The asteroid fall - which apparently occurred in Mexico's Yucatan Peninsula - triggered a global climate change that destroyed plant and animal life around the world.
But a mystery lingered: Fossil records showed that the cataclysm caused an unusual number of extinctions in North America. If the extinction was truly global, then why was North America so hard hit?
A simple yet dramatic solution appears in the November issue of Geology, in an article by planetary geoscientist Peter Schultz of Brown University in Providence, R.I., and paleoceanographer Steven D'Hondt of the University of Rhode Island.
They cite geological evidence that the asteroid didn't strike the Yucatan head-on. Rather, it approached from the southeast and hit at an angle, perhaps 20 to 30 degrees from horizontal.
The low-angle impact forced the searing debris toward the northwest - into a parabola-shaped kill zone over western and central North America.
This ``corridor of incineration,'' as Schultz and D'Hondt call it, perhaps ranged beyond the Pacific shore and the Appalachian Mountains and even all the way to Siberia.
The corridor of incineration hypothesis ``is going to be the prevailing theory from now on. It's been well-received and has no real detractors within the impact community,'' said Peter Sheehan, curator of geology at the Milwaukee Public Museum.
If human beings had existed in North America 65 million years ago, they might have witnessed a cataclysm worthy of biblical lore: First, a brilliant flash in the southeast as the asteroid rammed into the Yucatan, gouging out a crater about 120 miles wide and vaporizing the upper crust.
Then - if Schultz and D'Hondt are right - a brilliant, hot plume of vapor and incandescent debris would have arced across the sky at about 7 to 10 miles per second, then crashed onto North America. The scalding heat would have killed countless land-dwelling plants and animals. For example, some 90 percent of known types of leaf-bearing trees and plants died out, according to fossil records. Afterward, a slower-moving yet still rapid cloud of dust, debris and molten material swept over North America, ``adding more insult,'' Schultz said. ``Then an hour or more later, more dust began to fall from the sky as material was dispersed around the globe - and that may have gone on for days.''
A few fish and other aquatic creatures may have survived in cool rivers, lakes and coastal waters, Schultz adds.
LENGTH: Medium: 64 linesby CNB