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Murchison Meteorite

acids amino life organic

The Murchison meteorite was a meteorite that entered Earth's atmosphere in September 1969. The meteor fragmented before impact and remnants were recovered near Murchison, Australia (located about 60 mi [96.5 km] north of Melbourne). The fragments recovered dated to nearly five billion years ago—to the time greater than the estimated age of Earth. In addition to interest generated by the age of the meteorite, analysis of fragments revealed evidence of carbon-based compounds. The finds have fueled research into whether the organic compounds were formed from inorganic processes or are proof of extraterrestrial life dating to the time of Earth's creation.

In particular, it was the discovery of amino acids and the percentages of the differing types of amino acids found in the meteorite (e.g., the number of left handed amino acids vs. right handed amino acids), that made plausible the apparent evidence of extraterrestrial organic processes as opposed to biological contamination by terrestrial sources.

If the compounds prove to be from extraterrestrial life, this would constitute a profound discovery that would have far-reaching global scientific and social impact concerning prevailing hypotheses about the origin of life. For example, some scientists, notably one of the discoverers of the structure of DNA, Francis Crick, assert that in the period from the formation of Earth to the time of the deposition of the earliest discovered fossilized remains, there was insufficient time for evolutionary process to bring forth life in the abundance and variety demonstrated in the fossil record. Crick and others propose that a form of organic molecular "seeding" by meteorites exemplified by the Murchison meteorite (meteorites rich in complex carbon compounds) greatly reduced the time needed to develop life on Earth.

In fact, the proportions of the amino acids found in the Murchison meteorite approximated the proportions proposed to exist in the primitive atmosphere modeled in the Miller-Urey experiment. First conducted in 1953, University of Chicago researchers Stanley L. Miller and Harold C. Urey developed an experiment to test possible mechanisms in Earth's primitive atmosphere that could have produced organic molecules from inorganic processes. Methane (CH4), hydrogen (H2), and ammonia (NH3) gases were introduced into a moist environment above a water-containing flask. To simulate primitive lightning discharges, Miller supplied the system with electrical current. Within days organic compounds formed—including some amino acids. A classic experiment in molecular biology, the Miller-Urey test, established that the conditions that existed in Earth's primitive atmosphere were sufficient to produce amino acids, the subunits of proteins comprising and required by living organisms. It is possible, however, that extraterrestrial organic molecules could have accelerated the formation of terrestrial organic molecules by serving a molecular templates.

In 1997, NASA scientists announced evidence that the Murchison meteorite contained microfossils that resemble microorganisms. The microfossils were discovered in fresh breaks of meteorite material. The potential finding remains the subject of intense scientific study and debate.

University of Texas scientists Robert Folk and F. Leo Lynch also announced the observation of fossils of terrestrial nanobacteria in another carbonaceous chondrite meteorite named the Allende meteorite. Other research has demonstrated that the Murchison and Murray meteorites (a carbonaceous chondrite meteorite found in Kentucky) contain sugars critical for the development of life.

As of March, 2003, the scientific consensus in journals and other scholarly publications seemed to swing in favor of an interpretation that the Murchison meteorite did not provide definitive evidence of extra-terrestrial life and that many of physical attributes of the meteorite could be fully accounted for by inorganic processes or by contamination after impact. Scientific analysis and comparison continues, with scientists anticipating comparison of the properties observed in the Murchison meteorite with other meteorites.

Resources

Books

Bevan, Alex, et al. Meteorites: Journey Through Space and Time Washington, DC: Smithsonian Institution Press, 2002.

Zandra, Brigitte, and Monica Rotaru. Meteorites: Their Impact on Science and History. New York: Cambridge University Press, 2001.

Other

Duke University. "Cruising Chemistry—The Miller-Urey Ex periment" [cited March 10, 2003]. <http://www.chem.duke.edu/~jds/cruise_chem/Exobiology/miller.html>.


K. Lee Lerner

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