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Nearby supernova may have caused mini-extinction, scientists say

CHAMPAIGN, Ill. -- The recent discovery of the rare radioactive isotope iron-60 in deep-sea sediments could be the telltale sign of a killer supernova, a University of Illinois researcher says.

"A nearby supernova would bathe our planet in high-energy particles -- cosmic rays -- with potentially disastrous effects," said Brian Fields, a visiting professor of astronomy at the U. of I. "Increased cosmic-ray bombardment could have affected Earth's biosphere by enhancing the penetration of harmful solar ultraviolet radiation and by increasing the global cloud cover, leading to a 'cosmic-ray winter' and a mini-extinction."

In a paper scheduled to appear in New Astronomy, Fields and colleague John Ellis, a theoretical physicist at CERN, claim the measured iron-60 abundance cannot be explained by known sources, but could be the radioactive ashes of a supernova -- the explosion of a massive star. This cataclysmic explosion occurred 100 light-years from Earth about 5 million years ago, Fields and Ellis estimate.

The scientists based their analysis upon iron-60 data collected by a German team led by Gunther Korschinek of the Technical University of Munich.

"If these data are confirmed, together with their extraterrestrial origin, the implications are profound," Fields said. "They would constitute the first direct evidence that a supernova occurred near Earth in the fairly recent geologic past, with detectable effects on our planet."

Those effects include a huge increase in global cloud cover and a dramatic decrease in the protective ozone layer.

"A correlation has been observed between solar activity -- namely the sunspot cycle -- and the extent of Earth's cloud cover," Fields said. "Some researchers believe this correlation is due to modulation of the normal cosmic-ray flux observed today, caused by variations in the solar wind."

The enhanced cosmic-ray bombardment from a nearby supernova could create a large increase in global cloud cover, Fi
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Contact: James E. Kloeppel, Physical Sciences Editor
kloeppel@uiuc.edu
217-244-1073
University of Illinois at Urbana-Champaign
2-Aug-1999


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