Title: Dinosaur Killer.   
Subject(s): DINOSAURS -- Research; EXTINCTION (Biology)
Source: Popular Science, Apr99, Vol. 254 Issue 4, p37, 2/3p, 1
diagram, 1bw
Author(s): Stover, Dawn; Graham, David
Abstract: Provides information on a study conducted on the cause of
the death of dinosaurs 65 million years ago. Recovery of a material
whose composition resembles that of an asteroid; Other theory on the
death of dinosaurs.
AN: 1617072
ISSN: 0161-7370
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Database: MasterFILE Elite

Section: NEWSFRONTS: SCIENCE & TECHNOLOGY

GEOLOGY

DINOSAUR KILLER

MANY SCIENTISTS believe that a doomsday rock careened into Earth 65
million years ago, killing the dinosaurs in a climatic cataclysm. Now
a geochemist at the University of California in Los Angeles says he
has found a piece of the killer rock.

From deposits in the depths of the Pacific Ocean dating to that time,
Frank T. Kyte has recovered a fleck of material whose composition
resembles that of an asteroid.

Only a tenth of an inch in diameter, the fragment appears to have
iron, chromium, and iridium in the rich amounts known to exist in
meteorites, says Kyte. The coarse-grained sample also has evidence of
nickel and olivine. This combination is typical of a particular type
of meteorite, carbonaceous chondrites, which can come from asteroids.

"I think we were very lucky," Kyte says of the find. The sample
probably splintered off the asteroid as it exploded on impact.

Since the early 1990s, scientists have identified a buried crater off
the coast of Mexico's Yucatan peninsula as the site of the doomsday
impact. Kyte's rock lends credence to the hypothesis that an asteroid,
rather than a comet, created the crater.

Meanwhile, another discovery by California scientists provides
compelling evidence that an extraterrestrial impact, and not volcanoes
on Earth, caused the mass extinction that claimed two-thirds of the
species on Earth. Working at the University of California in San
Diego, Alexander Shukolyukov studied rare isotopes of chromium in a
thin layer of soot deposited across the Earth 65 million years
ago--soot that may have come from a volcanic eruption, some scientists
have argued. However, Shukolyukov found chromium 52 and chromium 53 in
ratios that exist in some meteorites but not on Earth, giving the soot
an unmistakable extraterrestrial signature. "Isotopes never lie," he
says.

Scientists can now focus on exactly how the dinosaurs died. Fires
caused by the heat of impact likely "roasted the dinosaurs in their
tracks," says H. Jay Melosh, a planetary scientist at the University
of Arizona. Also, sulfur-rich gases and debris from the impact may
have produced a sun-blocking haze that lingered for a few years.

DIAGRAM: The electron microscope image above...

PHOTOS (COLOR): ...shows the Interior of a tiny rock (below left)
believed to have been part of a killer asteroid. Above the rock is the
clay in which it was found.

~~~~~~~~

By DAWN STOVER and David Graham
_________________

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Source: Popular Science, Apr99, Vol. 254 Issue 4, p37, 2/3p, 1
diagram, 1bw.
Item Number: 1617072