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New ozone layer data article
EXPLODING STAR MAY HAVE CAUSED EARTHLY EXTINCTIONS 1/2/95
By PAUL RECER
WASHINGTON -- 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,
This, in turn, would break the food chain leading to mass extinctions, said
Schramm, coauthor of a study appearing Tuesday in the Proceedings of the
National Academy of Sciences.
An exploding star about 185 trillion 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 coauthor, 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
Schramm said the loss of the ozone layer would leave a chemical signature in
fossils from the extinction periods and that he is now 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
MERCURY CENTER CODE: N900 ID: me59148d
Transmitted: 95-01-02 21:03:27 EST