17 August 2009

Amino acids from outer space


The Murchison meteorite (above), found in Australia, is one of the rare carbonaceous chondritic meteorites, a class that is
composed of high percentages (3% to 22%) of water, as well as organic compounds. They are composed mainly of silicates, oxides and sulfides, while the minerals olivine and serpentine are characteristic. The presence of volatile organic chemicals and water indicates that they have not undergone significant heating (>200°C) since they formed, and their compositions are considered to be close to that of the solar nebula from which the solar system condensed.
Murchison has been found to contain
"glycine, alanine and glutamic acid as well as unusual ones like isovaline and pseudoleucine. The initial report stated that the amino acids were racemic (that is, the chirality of their enantiomers are equally left- and right-handed), indicating that they are not present due to terrestrial contamination... Serine and threonine, usually considered to be earthly contaminants, were conspicuously absent in the samples..."
Even more startling is the following:
A 2008 study showed that the Murchison meteorite contains nucleobases. Measured carbon isotope ratios indicate a non-terrestrial origin for these compounds… Measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of 44.5% and +37.7%, respectively, indicate a non-terrestrial origin for these compounds. These new results demonstrate that many organic compounds which are components of life on Earth, were already present in the early solar system and may have played a key role in life's origin.
I've previously briefly blogged about tardigrades; in the future it would be interesting to cover the topic of panspermia.

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