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(2) Scientists Pinpoint Time of Mass Extinction 250 Million Years Ago
[CND, 06/02/98] By studying zircon from Chinese rocks, Chinese and US
scientists found that the period of mass extinction on earth 250
million years ago lasted some 200,000 years, AFP reported. Five mass
extinctions are known to have occurred in history. The one under study
was the most profound. The cataclysmic heating of the earth dried up
rivers and lakes, dropped sea level to record lows, and wiped out over
three-quarters of the species on earth. The catastrophe surpassed the
one symbolized by the dinosaurs extinction 65 million years ago.
The 200,000-year period is just "a wink in the 4.6 billion-year history
of the earth," JIN Yugan, a researcher at the Nanjing Institute of
Geology and Paleontology said. The study shed no light on the cause of
such mass extinction. Scientists debate the theory that huge amounts of
dust and debris of a large asteroid or comet thrown into the atmosphere
created a "greenhouse effect" that in turn caused temperature rise. It
is suspected that this century's man-made pollution is causing global
warning in the same manner. (Shiji SHEN, YIN De An)
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