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Evidence of another Ancient Meteor Impact
Just as a meteor impact is believed to have brought about the extinction
of the dinosaurs 65 million years ago, scientists say a similar event
might have killed many fish and other creatures of an earlier era, about
380 million years ago.
Writing in today's issue of the journal Science, geologists at Louisiana
State University, the University of Texas at Arlington and the Scientific
Institute in Morocco report several lines of evidence that point to a
meteor impact that coincides with a mass extinction at a time when most
life was still contained in the oceans.
"It was probably a fairly significant impact," said Brooks Ellwood,
chairman of the geology and geophysics department at LSU and lead author
of the Science paper.
In the new research, Ellwood and his colleagues examined samples of rocks
from Morocco. In a layer 380 million years old, corresponding to the
extinction, they found grains of quartz with microscopic lines that form
when it is hit with a tremendous impact.
They also discovered spheres and crystals less than one-hundredth of an
inch wide that might be droplets of rock melted when a meteor struck. As
further evidence, they found elevated levels of elements such as nickel,
chromium and cobalt, all associated with meteors.
The scientists did not find these indicators in rocks several yards above
or below the extinction layer. They also reported chemical signs in carbon
in the rocks that indicate rapid, widespread deaths of organisms.
"All of those things together are very strong evidence that this is an
impact layer," Ellwood said.
It is not known where the meteor hit, and Ellwood said he has no estimate
of its size.
Ellwood also said that the researchers had found shocked quartz of the
same age in Spain but that that evidence has not been published. "I'm
pretty sure we're going to find it elsewhere," he said.