THE most dramatic crisis the living world has seen for hundreds of millions
of years was caused by a nearby supernova, a geologist in Hungary suggests. He
believes he has found debris from the exploded star.
The Permian extinction about 250 million years ago wiped out 90 per cent of
all species on Earth. Yet its cause has remained a mystery. Years of research
have failed to turn up any solid evidence for an asteroid impact comparable to
the one blamed for the death of the dinosaurs 65 million years ago.
Other causes that have been suggested include volcanism in Siberia and
widespread depletion of ocean oxygen. But neither theory is widely accepted,
because no one understands how these could have such a drastic effect.
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Astrophysicists first pointed to supernovae as possible culprits more than
two decades ago. John Ellis of CERN, the European Laboratory for Particle
Physics in Geneva, and David Schramm of the University of Chicago estimated that
every few hundred million years, a star explodes within a few tens of light
years from Earth. At that distance, high-energy particles and radiation from the
blast could strip away the Earth鈥檚 ozone layer for two hundred years, with
potentially deadly results.
With the ozone layer gone, ultraviolet light from the Sun and the supernova
would penetrate the atmosphere, changing its chemistry and killing surface
plants and animals. Hot gas and plasma from the explosion might also have
disrupted the Earth鈥檚 magnetosphere, allowing cosmic rays to reach the ground
and causing more devastation, says Imre Toth, an astronomer at Konkoly
Observatory in Budapest.
Toth鈥檚 colleague, Csaba Detre of the Geological Institute of Hungary,
also in Budapest, says he has now found what could be the debris of an
exploded star鈥攎etal-rich globules 3 to 20 micrometres in diameter. These
appear in rocks from the period in Japan, China, India, Armenia, Iran and
Hungary. The abundance of elements such as aluminium in the globules suggest
they came from outside the Solar System, he says.
Detre鈥檚 discoveries, announced last month at the Lunar and Planetary Science
Conference in Houston, left other researchers 鈥渧ery interested鈥�, says geologist
Thomas Ahrens at the California Institute of Technology. But the case is far
from proven. 鈥淭here are several big leaps that I have trouble with,鈥� says Rich
Muller of the Lawrence Berkeley Laboratory in California.
Detre now plans to firm up his data by analysing the isotopes and trace
elements in the globules. He also hopes to pin down their ages, which are not
easy to gauge from most deposits of that period.