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RE: Scientists think sunburst triggered ancient mass extinction
I wonder if anyone has taken into theoretical account the possibility of an orbital shift in the earth's relation to our sun as a cause of the onset of the ice age.
-----Original Message-----
From: Susan L Gawarecki [mailto:loc@icx.net]
Sent: Thursday, January 08, 2004 10:33 AM
To: RADSAFE
Subject: Scientists think sunburst triggered ancient mass extinction
Scientists think sunburst triggered ancient mass extinction
January 8, 2004
http://www.enn.com/news/2004-01-08/s_11839.asp
By Paul Recer, Associated Press
ATLANTA — The second-largest extinction in the Earth's history, the
killing of two-thirds of all species, may have been caused by
ultraviolet radiation from the sun after gamma rays destroyed the
Earth's ozone layer.
Astronomers are proposing that a supernova exploded within 10,000 light
years of the Earth, destroying the chemistry of the atmosphere and
allowing the sun's ultraviolet rays to cook fragile, unprotected life forms.
All this happened some 440 million years ago and led to what is known as
the Ordovician extinction, the second most severe of the planet's five
great periods of extinction.
"The prevailing theory for that extinction has been an ice age," said
Adrian L. Melott, a University of Kansas astronomer. "We think there is
very good circumstantial evidence for a gamma ray burst."
Melott is the leader of a team, which includes some astronomers from the
National Aeronautics and Space Administration, that presented the theory
Wednesday at the national meeting of the American Astronomical Society.
Fossil records for the Ordovician extinction show an abrupt
disappearance of two-thirds of all species on the planet. Those records
also show that an ice age that lasted more than a half million years
started during the same period.
Melott said a gamma ray burst would explain both phenomena.
He said a gamma ray beam striking the Earth would break up molecules in
the stratosphere, causing the formation of nitrous oxide and other
chemicals that would destroy the ozone layer and shroud the planet in a
brown smog.
"The sky would get brown, but there would be intense ultraviolet
radiation from the sun striking the surface," he said. The radiation
would be at least 50 times above normal, powerful enough to killed
exposed life.
In a second effect, the brown smog would cause the Earth to cool,
triggering an ice age, Melott said.
The extinction "could have been a one-two punch," said Bruce S.
Lieberman, a paleontologist at the University of Kansas and a co-author
of the theory. "Our theory builds on earlier theories" that included an
ice age.
Before the extinction, the Earth was unusually warm. Melott said climate
experts have been unable to find a model that would explain the sudden
onset of massive glaciers.
"They need something to jump start the ice age," he said. "The gamma ray
burst could have done it."
Jere H. Lipps, a paleobiologist at the University of California,
Berkeley, said gamma rays as a source of the Ordovician extinction
should be regarded as only one of several theories. "It is a hypothesis
that should be tested," Lipps said.
He said the widely-accepted idea that the dinosaurs were wiped out by an
asteroid 65 million years ago started out as a "wild idea" but that it
gained wide support after other research.
Most of the life killed in the Ordovician extinction were primitive sea
creatures. Those that lived at or near the surface would be greatest
risk from the ultraviolet radiation. Melott said the species killed
lived in shallow waters or reproduced with larvae that spent part of
their lives near the water surface. Animals living in deep water were
not harmed.
There were only primitive plants living on land, but they, too, would
have been affected, he said.
Melott said it is almost certain that Earth has been zapped by a gamma
rays several times in its 4.5 billion year history.
"You can expect a dangerous gamma ray burst every few hundred million
years," he said. "It could happen tomorrow or it could be millions of
years."
Supernovae, the source of gamma rays, usually leave behind remnant
clouds of dust, shock waves and black holes that can be detected for
millions of years. Melott said there is no known evidence of such a
nearby supernova, but that in 440 million years the Milky Way would have
rotated almost twice and traces of the explosion could have been moved
during that time.
The Ordovician was the first of five great extinctions in history.
The Devonian, 360 million years ago, killed 60 percent of all species;
the Permian-Triassic, 250 million years ago, killed 90 percent of all
life; the late Triassic, 220 million years ago, killed half of all
species; and the Cretacious-Tertiary event destroyed the dinosaurs and
half of all other species about 65 million years ago.
--
.....................................................
Susan L. Gawarecki, Ph.D., Executive Director
Oak Ridge Reservation Local Oversight Committee
102 Robertsville Road, Suite B, Oak Ridge, TN 37830
Toll free 888-770-3073 ~ www.local-oversight.org
.....................................................
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