Scientists think sunburst triggered ancient mass extinction

[Susan L Gawarecki <loc@icx.net>]

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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