Meteorites A Rich
Source For Primordial Soup
(13 March 2008) The organic soup that
spawned life on Earth may have gotten generous helpings from outer space,
according to a new study.
Scientists at the Carnegie Institution
have discovered concentrations of amino acids in two meteorites that are more
than ten times higher than levels previously measured in other similar
meteorites. This result suggests that the early solar system was far richer in
the organic building blocks of life than scientists had thought, and that
fallout from space may have spiked Earth's primordial broth.
The study,
by Marilyn Fogel of Carnegie's Geophysical Laboratory and Conel Alexander of
the Department of Terrestrial Magnetism with Zita Martins of Imperial College
London and two colleagues, will be published in Meteoritics and Planetary
Science.*
Amino acids are organic molecules that form the backbone of
proteins, which in turn build many of the structures and drive many of the
chemical reactions inside living cells. The production of proteins is believed
to constitute one of the first steps in the emergence of life. Scientists have
determined that amino acids could also have formed in some environments on the
early Earth, but the presence of these compounds in certain meteorites has led
many researchers to look to space as a source.
The meteorites used for
the study were collected in Antarctica in 1992 and 1995 and held in the
meteorite collection at the NASA Johnson Space Center in Houston, Texas.
Antarctica is the world's richest hunting ground for meteorites, which are
naturally concentrated in so-called blue ice regions and held in cold storage
by the ice.
For the amino acid study, the researchers took small samples
from three meteorites of a rare type called CR chondrites, thought to contain
the oldest and the most primitive organic materials found in meteorites. CR
chondrites date from the time of the solar system's formation. During an early
phase of their history the meteorites were part of a larger "parent body," such
as an asteroid, which later was shattered by impacts.
The analysis
revealed that while one sample showed a relatively low abundance of amino
acids, the other two meteorites had the highest ever seen in primitive
meteorites--180 and 249 ppm (parts per million). Other primitive meteorites
that have been studied generally have amino acid concentrations of 15 ppm or
less. Because organic molecules from extra-terrestrial sources have ratios of
carbon isotopes different from those of Earthly biological sources, the
researchers were able to rule out contamination as a factor in their
result.
"The amino acids probably formed within the parent body before
it broke up," says Alexander. "For instance. ammonia and other chemical
precursors from the solar nebula, or even the interstellar medium, could have
combined in the presence of water to make the amino acids. Then, after the
break up, some of the fragments could have showered down onto the Earth and the
other terrestrial planets. These same precursors are likely to have been
present in other primitive bodies, such as comets, that were also raining
material onto the early Earth. "
* Z. Martins, C. M. O'D. Alexander, G.
E.Orzechowska, M. L. Fogel, and P. Ehrenfreund, Indigenous amino acids in
primitive CR meteorites. Meteoritics and Planetary Science.
Funding for
Fogel and Alexander provided in part by NASA's Origins of Solar Systems program
and the NASA Astrobiology Institute.
The Carnegie Institution has been a
pioneering force in basic scientific research since 1902. It is a private,
non-profit organisation with six research departments throughout the U.S.
Carnegie scientists are leaders in plant biology, developmental biology,
astronomy, materials science, global ecology, and Earth and planetary
science.
The NASA Astrobiology Institute (NAI), founded in 1998, is a
partnership between NASA, 16 major U.S. teams, and five international
consortia. NAI's goal is to promote, conduct, and lead integrated,
multidisciplinary astrobiology research and to train a new generation of
astrobiology researchers.
(source: Carnegie Institution)
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