A new area of glass fragments thought to date from a meteorite
impact almost half a million years ago has been discovered by an
international team led by a scientist at the Open University.

The glass is found in an area of the Pampas region of Argentina, a
site that became famous in 1992 when a US-led team identified ten
elongate shallow depressions — each kilometres long. They suggested
they had been formed by the low-angle impact of an asteroid that had
hit the Earth like a bouncing bomb. Meteorite glass was found in
several of these depressions.

The new study of part of the Pampas region revealed more than 400
depressions, spread over an area that is too large to be the result
of the low-angle impact that the scientists of the early 90s
suggested. Instead, the team believes the depressions in the area
around the city of Rio Cuarto were the result of wind action.

The Open University’s Phil Bland, a Royal Society university research
fellow, and Dr Simon Kelley, also from the OU, were joined by
researchers from Brazil, the USA, Australia, Russia and Argentina
for their work. They initially assessed satellite images of the area
before undertaking field visits to 52 of the features.

The team believes that the fragments of glass it dated at the Rio
Cuarto depressions are of a similar age to that of glass recovered
800km away, indicating that glass is found over a huge region and
is not confined to shallow depressions. The material may be tektite
glass — pieces of fused rock and soil formed when a large meteorite
strikes the Earth — from an impact event about half a million years
ago.

Glass would have splashed out of the impact, showering down over the
surrounding area, and is found today in places where the wind has
blown soil away — the original shallow depressions.

Phil Bland said: "It seems plausible that the material we found is
representative of a widespread tektite-strewn field in Argentina
that is about 480,000 years old. We suggest that a recent, possibly
well-preserved, complex crater remains to be discovered beneath the
Pampean Plain of Argentina."

EDITOR’S NOTES

The team’s paper A Possible Tektite-Strewn Field in the Argentinian
Pampa is published in the 10 May 2002 issue of Science.

Phil Bland is a research fellow working in the Open University’s
Planetary and Space Sciences Research Institute; Dr Simon Kelley
works in the university’s Department of Earth Sciences. The team
was also helped by Vanessa Evers, of the university’s Institute
of Educational Technology.