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The dominance of “left-handed” amino acids
Meteorite Bombardment Responsible for Earth Life Characteristics
By Joshua Hill Monday, April 7, 2008There is nothing quite as exhilarating for me than to learn something new. And thanks to a Columbia University professor, it looks as though the latest factoid to implant itself in to my brain is the possibility that the almost exclusive left-handed amino acid trait in human life could have come from outer-space.
When presented with the sentence “Scientists presented evidence today that desert heat, a little water, and meteorite impacts may have been enough to cook up one of the first prerequisites for life: The dominance of “left-handed” amino acids, the building blocks of life on this planet,” I immediately went in to research mode.
A note on NASA’s Ames Research Center website describes this “left handed” trait as a “chiral” molecule. The left handed description is just that, a description, of the amino acids in question; they are not – from all I can tell – referring to some acid that gives us a left or right handed predisposition.
“Like left and right hands that have a thumb, fingers in the same order, but are mirror images and not the same, chiral molecules have the same things attached in the same order, but are mirror images and not the same.”
The website goes on to detail that “Although most amino acids can exist in both left and right handed forms, Life on Earth is made of left handed amino acids, almost exclusively. No one knows why this is the case.”
All of that leads me to Ronald Breslow, Ph.D., University Professor, Columbia University, and former American Chemical Society President, and his report presented at the 235th national meeting of the ACS.
His report essentially posits that this left handed exclusivity of humans is the result of a meteorite from outer space.
“These meteorites were bringing in what I call the ‘seeds of chirality,’” stated Breslow. “If you have a universe that was just the mirror image of the one we know about, then in fact, presumably it would have right-handed amino acids. That’s why I’m only half kidding when I say there is a guy on the other side of the universe with his heart on the right hand side.”
These “seeds” of amino acids formed in interstellar space, most likely on asteroids or meteorites. While at the beginning of their life spans the rocks are inhabited by both left and right handed amino acids, when they pass a neutron star, their light rays trigger selective destruction of one form of amino acid. ‘The stars emit circularly polarized light—in one direction, its rays are polarized to the right. 180 degrees in the other direction, the star emits left-polarized light.’
Breslow pointed to previous experiments that showed all earthbound meteors catch an excess of one of the two polarized rays, and that circularly polarized light selectively destroys one chiral form of amino acids over the other. Using evidence found on the surface of rocks which had rocketed in to our planet in Australia and Tennessee.
Breslow simulated what would happen after the dust had settled if such a rock had crashed in to our planet, and under ““credible prebiotic conditions”— desert-like temperatures and a little bit of water — he exposed amino acid chemical precursors to those amino acids found on meteorites.”
More than just suggesting how our life came to exhibit this left-handed amino tendency, Breslow’s work helps point to life elsewhere. “This work is related to the probability that there is life somewhere else,” said Breslow. “Everything that is going on on Earth occurred because the meteorites happened to land here. But they are obviously landing in other places. If there is another planet that has the water and all of the things that are needed for life, you should be able to get the same process rolling.”
