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August 24, 2001 07:00 CDT

The first results are in from the organic analysis of
the Tagish Lake Meteorite, a rare, carbon-rich meteorite
classified as a "carbonaceous chondrite". The meteorite
fell on a frozen Canadian lake in January 2000 and is
the most pristine specimen ever studied of this group of
important space objects.

Carbonaceous chondrite meteorites contain important
clues regarding the evolution of carbon compounds in our
solar system preceding the origin of life.

The analysis, conducted by a team headed by chemist
Sandra Pizzarello, a research scientist at Arizona State
University, on 4.5 grams taken from the sealed interior
of the meteorite, found organic compounds in the
meteorite with some similarities to other known
carbonaceous chondrites. However, there were also clear
differences. The largest of them was the near-absence of
the amino acids found in some meteorites studied before.

In an article appearing in the August 24 issue of the
online journal Science Express, the team notes that the
chemistry of the Tagish Lake Meteorite appears to
preserve organics that accumulated or developed in the
early history of the Solar System. These include
molecular bubbles of carbon containing the noble gasses
helium and argon in a ratio similar to the gas and dust
cloud that formed the planets. This may reflect an early
stage in a process of evolution of complex carbon
compounds in space.

"The chemistry here is different from that we have seen
in any other meteorite," said Pizzarello. "It's simple,
when compared with Murchison (a famous carbon meteorite
found in Australia in 1969 that contained numerous amino
acids and a variety of other organic compounds) and
probably represents a separate line of chemical
evolution. However, it still includes compounds that are
identical to biomolecules."

Other members of the research team include Yongsong
Huang from the Department of Geological Sciences at
Brown University; Luann Becker from the Institute for
Crustal Studies at the University of California Santa
Barbara; Robert J. Poreda from the Department of Earth
and Environmental Sciences, University of Rochester;
George Cooper from the NASA Ames Research Center; and
Ronald A. Nieman and Michael Williams, both also from
ASU.

The Science paper notes that many of the organic
compounds found in the Tagish Lake sample have also been
found in other meteorites, but that the distribution of
compounds is different, particularly for the amino acids
and carboxylic acids.

"Some people have been disappointed that we found
virtually no amino acids, but scientifically this is
very exciting," Pizzarello said. "This meteorite shows
the complexity of the history of organic compounds in
space -- it seems to have had a distinct evolution."

"We found some compounds identical to some in Murchison
that show the same 'interstellar connection' in their
abundance of deuterium (heavy hydrogen), while some
others differ from Murchison in amounts and variety,"
said Pizzarello, meaning that for some groups of organic
molecules, only the simplest species were found in
Tagish Lake, as opposed to a broader distribution of
species found in Murchison. "Overall, Tagish Lake
represents a simpler, more unaltered stage than we have
seen before."

The analyses gives evidence for what Pizzarello calls "a
different outcome" of organic chemical evolution in
space likely to have happened during the formation and
development of the solar system, "but one that still
might have contributed molecular precursors of
biomolecules to the origins of life," she noted.

Source: Press Release
Cosmiverse Staff Writer
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