Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, January 5, 1995 TAG: 9501050080
SECTION: NATIONAL/INTERNATIONAL PAGE: A9 EDITION: METRO
SOURCE: ASSOCIATED PRESS
DATELINE: WASHINGTON LENGTH: Medium
A mass extinction on Earth 225 million years ago may have been caused by an exploding star that zapped the planet with radiation and stripped away the protective ozone layer, a scientist says.
An explosion of a supernova within 30 light years of Earth would bathe the planet's upper atmosphere with powerful gamma- and cosmic-ray radiation, setting off a chemical reaction that would destroy the ozone layer, said David N. Schramm, an astrophysicist at the University of Chicago.
Recent research suggests that if the ozone layer were wiped out, ultraviolet radiation from the sun could soak the unprotected Earth and kill plants, Schramm said.
This, in turn, would break the food chain, leading to mass extinctions, said Schramm, co-author of a study that appeared Tuesday in the Proceedings of the National Academy of Sciences.
An exploding star about 185trillion miles away would create enough gamma radiation to thin the ozone for many years, he said.
``Intense ionizing radiation in the upper atmosphere would break up molecules of oxygen and nitrogen and enable them to capture the ozone,'' said Schramm. ``It would start a chemical reaction in the upper atmosphere, and once it's started, the ozone is depleted.''
That supernovae may have caused mass extinction is not a new idea, but the mathematical model created by Schramm and his co-author, John Ellis of the European Organization for Nuclear Research, is the first to suggest that such exploding stars could destroy the ozone layer.
Alastair Cameron of the Center for Astrophysics at Harvard University in Cambridge, Mass., said the theory was not implausible and merited serious consideration. Cameron said he would have to study the mathematical model to fully evaluate the theory.
Kevin Pope, a NASA contract scientist employed by Geo Eco Arc Research at the Jet Propulsion Laboratory, said the idea should be studied.
``To me, it sounds theoretically possible,'' said Pope, ``but I know of no independent evidence to support it. To be useful, it would have to be tested.''
Schramm said that the loss of the ozone layer would leave a chemical signature in fossils from the extinction periods and that he is conducting experiments to test for this chemistry.
There have been at least five major extinctions in the 600 million-year history of life on Earth.
The most famous, 65 million years ago, wiped out the dinosaurs. The extinction 225 million years ago was the most severe, killing 95 percent of all species. It ended the Permian geologic period and was followed by the rise of the age of reptiles.
Extinctions also occurred about 450 million, 350 million and 190 million years ago.
by CNB