K-T extinction event mystery may be solved

Jeff Poling

The North American continent and many of its creatures were barbecued 65 million years ago in an immense, white-hot "corridor of incineration" resulting from an asteroid impact in Mexico, scientists say.

The theory, based partly on laboratory experiments at NASA's Ames Research Center in Mountain View, California, may solve an important mystery.

Over the last decade, many Earth scientists have accepted the theory that an asteroid, comet or bolide impact wiped out the non-avian dinosaurs and many other species 65 million years ago. The impact, which apparently occurred in Mexico's Yucatan Peninsula, may have triggered a global climate change that destroyed plant and animal life around the world.

However, a mystery emerged as more and more data was gathered supporting the theory. The fossil record showed that the impact event caused an unusually high number of extinctions in North America. Why?

A possible solution to the mystery appears in an article in the November 1996 issue of Geology by planetary geoscientist Peter H. Schultz of Brown University in Providence, Rhode Island, and paleocoeanographer Steven D'Hondt of the University of Rhode Island.

In the article they cite geological evidence that the asteroid or other object didn't strike the Yucatan head-on; rather, it approached from the southeast and hit at an angle, perhaps 20 to 30 degrees from the horizontal.

The 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 called it, may have ranged beyond the Pacific shore and the Appalachian Mountains, and possibly all the way to Siberia.

Schultz simulated the asteroid impact in lab experiments at NASA-Ames. He used a hypervelocity gas gun that fires projectiles (such as quarter-inch metallic spheres) at 4 miles per second at low angles toward targets resembling the Yucatan surface, "literally dirt or carbonates." The collisions generated extremely hot plasmas of ionized gas, "as hot as the sun's surface, up to 10,000 degrees Fahrenheit."

Creatures living at the time of the impact 65 million years ago, assuming they weren't actually in the kill zone, might have witnessed the following sequence of events:

1. A brilliant flash erupted in the southeast as the asteroid rammed into Mexico's Yucatan Peninsula, gouging out a crater about 120 miles wide and vaporizing the upper crust.
2. A brilliant, hot plume of vapor and incandescent "sun-bright" debris arced across the sky at about 7 to 10 miles per second, then crashed onto North America.
3. Scalding heat killed countless land-dwelling plants and animals. For example, 90 percent of known types of leaf-bearing trees and plants became extinct, according to the fossil record.
4. A slower yet still high-velocity cloud of dust, debris and molten material then swept over North America.
5. Finally, an hour or more after the impact, more dust began to fall from the sky, perhaps for days, as material was dispersed around the globe.

A few fish and other aquatic creatures may have survived in cool rivers, lakes and coastal waters, Schultz says.

1. Unkown. 1996. Asteroid mystery may be solved. The Columbus Dispatch, 10 November, sec. A, 13.