Great Impact May Have Caused 'Great Dying'
(From the July/August 2004 issue of StarDate magazine)
A submerged peak, a thin layer of melted rock, and slivers of deformed
quartz suggest that an asteroid or comet slammed into Earth 251 million
years ago, killing most of the life on Earth, according to an international
research team. The impact rivaled the one that may have killed the dinosaurs
65 million years ago.
About 90 percent of all species of marine life and 80 percent of land
species perished in the “Great Dying” at the end of the Permian era. It is
the most extensive mass extinction yet discovered, exceeding the
Cretaceous-ending event that killed the dinosaurs.
A team headed by Luann Becker of the University of California, Santa
Barbara, reported new evidence that an impact caused the Great Dying in a
paper published May 13 in the online version of Science.
Researchers had already hypothesized that a submerged peak, known as Bedout
High, north of Australia was formed by an ancient impact. The new report
shows that the crater, which is buried under deep sediments, is about 125
miles (200 km) wide — roughly the same as the Chicxulub crater left by the
dinosaur-killing impact.
The new report also includes an analysis of core samples taken from the
floor of the crater by an Australian oil company during the 1970s and ’80s.
The cores showed a layer of melted rock that dates to the time of the
crater’s formation. In addition, researchers discovered “shocked quartz” —
quartz fractured by the force of a powerful impact — in rock layers in
Australia that also date to the time of the possible impact.
But the researchers did not find shocked quartz in the core samples, so
their identification of the sea floor as a possible impact crater remains
uncertain. In addition, many researchers believe that a massive outpouring
of lava in Siberia was responsible for the Great Dying.
Some scientists have suggested that a giant impact could trigger large-scale
volcanic events, creating a one-two punch against terrestrial life. The
impact could heat Earth’s atmosphere, blast enough debris into the air to
block sunlight, and create acid rain. It also might trigger volcanic
eruptions, which would extend the havoc. Some scientists point out that the
Great Dying stretched across perhaps 200,000 years, suggesting that it was
the result of a combination of events, not a single, sudden blow to Earth’s
ecosystem. -- Damond Benningfield
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