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By
Paul Rincon
Evidence for what may be a large and relatively recent
impact crater has been found off the coast of Antarctica.
Scientists say the evidence, if correct, points to a
space rock some 5km across having crashed into the Ross
Sea about three million years ago.
This could have generated a huge tsunami, according to
a member of the team investigating the collision.
Details were reported at the Lunar and Planetary Science
Conference in Houston, Texas.
Glass hints
Researchers from the Lamont-Doherty Earth Observatory
in New York have been studying a 100km-wide depression,
known as Bowers Crater, under the Ross Sea.
Team members examined cores drilled from around the area
to look for evidence of an impact.
In the cores, they found microscopic glassy grains shaped
like teardrops, spheres and dumbbells which are collectively
known as tektites.
Some scientists believe these are created when rock fragments
are hurled high up into the atmosphere by the impact of
a large meteoroid or asteroid, and then partially re-melt
as they fall back to the ground.
Other glasses were also found. These are thought to have
been formed by cooling of the melted rock and sediment.
Similar glasses can be formed through volcanism, but the
Ross Sea specimens seem to have a distinct structure under
the microscope.
Wave trace
The findings alone do not prove there was an impact in
the area a few million years ago, but team member Dallas
Abbott says she hopes to search the core material further
for a mineral called shocked quartz.
This type of quartz can be distinguished from normal quartz
by characteristic lines visible under the microscope which
are thought to be formed by the intense pressure of an
impact.
The presence of this mineral is considered most diagnostic
of a space collision.
Dr Abbott told the BBC News website that an impact in
the Ross Sea would have generated a "pretty big tsunami".
The waves could have crashed against the shores of South
America; but, she added, the geological history of that
continent made it unlikely that evidence of this event
would be found.
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BBC
News -
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