Washington, April 7 : Scientists have found evidence that meteorites may have delivered "left-handed" amino acids - the building blocks of life, to Earth.
Ronald Breslow, professor, Columbia University, has reported the finding.
Though Earth was a hot, dry and lifeless planet three or four billion years ago, some scientists believe that a meteor slammed into the desert plains at over ten thousand miles per hour, planting the chemical seeds of life.
Now, Breslow has come up with new evidence in support of this theory.
Chains of amino acids make up the protein found in people, plants, and all other forms of life on Earth. There are two orientations of amino acids, left and right, which mirror each other in the same way your hands do. This is known as "chirality."
"In order for life to arise, proteins must contain only one chiral form of amino acids, left or right," Breslow noted.
With the exception of a few right-handed amino acid-based bacteria, left-handed "L-amino acids" dominate on earth.
According to Breslow, these amino acids "seeds" formed in interstellar space, possibly on asteroids as they careened through space, delivering to Earth the left-handed protein units.
"These meteorites were bringing in what I call the 'seeds of chirality,'" he said.
Evidence of left-handed excess was found on the surfaces of meteorites that have crashed into Earth even within the last hundred years, landing in Australia and Tennessee.
Breslow simulated what occurred after the dust settled following a meteor bombardment, when the amino acids on the meteor mixed with the primordial soup.
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.
Breslow and Columbia chemistry grad student Mindy Levine found that these cosmic amino acids could directly transfer their chirality to simple amino acids found in living things.
"On the prebiotic Earth, this transfer left a slight excess of left-handed amino acids," Breslow said.
His next experiment replicated the chemistry that led to the amplification and eventual dominance of left-handed amino acids. He started with a five percent excess of one form of amino acid in water and dissolved it.
Breslow found that the left and right-handed amino acids would bind together as they crystallized from water. The left-right bound amino acids left the solution as water evaporated, leaving behind increasing amounts of the left-amino acid in solution.
Eventually, the amino acid in excess became ubiquitous as it was used selectively by living organisms.
"Everything that is going on on Earth occurred because the meteorites happened to land here," said Breslow.