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Left-handed amino acids in Tagish Lake meteorite complicate the search for life in outer space.
Planetary geologists have found unusual chemistry in the Tagish Lake meteorite. Amino acids found in fragments show a preponderance of left-handed amino acids. Since an unequal proportion of left- and right-handed organic molecules is normally considered “a signature of life”—and since this meteorite contains no evidence of biological inhabitants past or present—the search for extraterrestrial life just got a bit more complicated.
Some organic (carbon-containing) molecules can exist in mirror image forms. Such compounds are called chiral—pronounced kīrəl, like “spiral” with a k. Synthetic organic compounds generally consist of equal proportions of left- and right-handed mirror image forms. But when living things produce organic compounds, the products are homochiral—consisting of only one of the possible mirrored forms. Biochemical processes require specific mirror-image forms of molecules to function. (This is the reason the “DL” vitamins you can buy are usually cheaper than the corresponding “L” forms of vitamins—only the “L” part is actually usable by your body, but the “DL” is usually cheaper to produce.)
Organic compounds have been found in meteorites but generally as chiral mixtures. Their non-specific chirality attests to their non-biological origin and their non-usefulness as starting molecules that some evolutionists suggest “seeded” earth with the chemical building blocks for life.
Organic compounds have been found in meteorites but generally as chiral mixtures.
We reported in June that the Tagish Lake meteorite, which fell over British Columbia in 2000, contained amino acids. Further analysis by Daniel Glavin’s team, reported July 31 in the journal Meteoritics and Planetary Science, has now demonstrated that 43 to 59% of the amino acids aspartic acid and glutamic acid present in the fragments is left-handed. All of the amino acid alanine, however, is present in the usual 50-50 proportion. Other tests rule out the possibility of terrestrial contamination.
The investigators suggest a way in which ordinary chemical and physical processes can produce chirality. (They do not suggest a biological origin, and the compounds are not 100% homochiral like those produced by living cells.) Only left-handed forms of aspartic and glutamic acids can form crystals after being dissolved in water. Alanine molecules are able to fit into crystals regardless of their chirality. The team hypothesizes the amino acids in the meteorite at some time in the rock’s history dissolved in water, preferentially concentrating and preserving the organic compounds in crystalline form.1
A commonly noted problem—though by no means the only or even the greatest one arguing against the possibility of the random evolution of life from non-living chemicals—has been the fact that life is based on complex homochiral (left-handed) biomolecules that could not have evolved randomly. The finding of a slight excess of one of the chiral forms of simple organic molecules in the Murcheson meteorite (Australia, 1969) led Dr. Ronald Breslow to publish research showing that chemical reactions starting with homochiral molecules end up producing homochiral molecules. (Breslow’s work became famous for his suggestion that advanced alien dinosaurs might be a danger to humanity.)
Any strategies designed to search for life based on looking for this excess require serious rethinking.
Thus, some evolutionists suggest that homochiral organic molecules dropped on earth from outer space could have provided the chiral chemicals needed to produce life. But Dr. Breslow, whose paper raised this possibility, admitted there is no known way such “building blocks could assemble into structures with the exciting properties of life.”2
Thanks to this discovery, scientists searching for extraterrestrial life can no longer rely on the presence of homochiral molecules to indicate the success of their search. For instance, Alberto Fairen of the SETI project notes, “As evidence mounts that [left-handed] excess occurs naturally across bodies in the solar system, any strategies designed to search for life based on looking for this excess require serious rethinking.” Harald Steininger of the ExoMars alien-hunting project of the European Space Agency indicates he’s not worried, though. He says, “A swimming pool full of [left-handed] amino acids is not alive. Life shows in many different aspects, and chirality is only one of them.” Nevertheless, many evolutionary scientists still presume earth received a delivery of pre-biotic space dust to start the evolutionary ball rolling.
These researchers have not only documented an unexpected chiral specificity to non-biologic organic molecules but also proposed a way in which non-biological chemistry could have produced that imbalance. They have not, however, shown a way such molecules—even preferentially left-handed ones—could randomly interact to produce life. A whole swimming pool full of left-handed amino acids and even additional chemical ingredients of life would still lack the organizing information and machinery to produce living cells. Nothing in nature has ever demonstrated a way in which life can randomly emerge from non-living chemicals. Observational science continues to confirm the law of biogenesis—life comes from life. To call these amino acids “pre-biotic” is to presume without proof (and thereby mislead the public) that life could spring into existence without God.
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