UltimateReality
Active Member
- Jan 13, 2012
- 2,790
- 15
- 36
"A curious aspect of Earth's life forms is that they contain (with few exceptions) only left-handed amino acids. In contrast, when scientists synthesize amino acids from nonchiral precursors, the result is always a "racemic" mixture - equal numbers of right- and left-handed forms. Scientists have been unable to perform any experiment that, when starting with conditions believed to emulate those of early Earth, results in a near-total dominance of left-handed amino acids, says George Cody, a geochemist at the Carnegie Institute of Washington."
"But chemical studies of these meteorites have often been challenged as unreliable by scientists claiming that contamination has occurred through exposure, storage, or handling. Over time, says Jeff Bada, of the Scripps Institute of Oceanography, even carefully stored meteorites gradually become contaminated.
If organic compounds such as amino acids from Earth's biosphere have penetrated meteorite samples, they would no longer be representative of early solar system chemistry, nor could they provide evidence of an extraterrestrial source for the components of Earth's first life. But figuring out whether or not a meteorite has been contaminated has proven to be a thorny problem."
"The investigators found that the stable isotope ratios were identical for the left-handed and right-handed forms. This, says Engel, indicates, that they had to have come from the same source - that is, not from Earth. If, he argues, a portion of the left-handed forms were from terrestrial organics, these forms would have exhibited a different isotopic signature than the right-handed forms. They would have contained more light carbon and nitrogen.
Kvenvolden and Bada aren't convinced. The new stable-isotope evidence notwithstanding, says Kvenvolden, a left-handed excess like that found in previous research by Engel and Macko, "is inconsistent with the observations of Cronin, Pizzarello and myself for protein amino acids in the meteorite." Kvenvolden firmly believes Engel and Macko were seeing contamination."
Murchison's Amino Acids: Tainted Evidence?
"But chemical studies of these meteorites have often been challenged as unreliable by scientists claiming that contamination has occurred through exposure, storage, or handling. Over time, says Jeff Bada, of the Scripps Institute of Oceanography, even carefully stored meteorites gradually become contaminated.
If organic compounds such as amino acids from Earth's biosphere have penetrated meteorite samples, they would no longer be representative of early solar system chemistry, nor could they provide evidence of an extraterrestrial source for the components of Earth's first life. But figuring out whether or not a meteorite has been contaminated has proven to be a thorny problem."
"The investigators found that the stable isotope ratios were identical for the left-handed and right-handed forms. This, says Engel, indicates, that they had to have come from the same source - that is, not from Earth. If, he argues, a portion of the left-handed forms were from terrestrial organics, these forms would have exhibited a different isotopic signature than the right-handed forms. They would have contained more light carbon and nitrogen.
Kvenvolden and Bada aren't convinced. The new stable-isotope evidence notwithstanding, says Kvenvolden, a left-handed excess like that found in previous research by Engel and Macko, "is inconsistent with the observations of Cronin, Pizzarello and myself for protein amino acids in the meteorite." Kvenvolden firmly believes Engel and Macko were seeing contamination."
Murchison's Amino Acids: Tainted Evidence?
Last edited: