One of the puzzles regarding the rise of life on earth is the fact that all life makes use of so-called “left-handed” amino acids, rather than their right-handed counterparts. Recent analysis of meteorites gives one possible explanation for this: left-handed amino acids were more common in the early solar system and therefore on early earth, so life made do with what was available. Science reports:
“Since the days of Louis Pasteur, scientists have known that amino acids, the building blocks of proteins, come in two varieties. There are left-handed and right-handed versions, with a hydrogen atom representing the “thumb” in both cases. For unknown reasons, organisms on Earth contain only left-handed amino acids. The question is why?
For the past 4 years, astrobiologists Daniel Glavin and Jason Dworkin of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, have been searching for the answer by carefully studying the molecular deposits inside six meteorites found in Antarctica and Australia. The space rocks are more than 4.5 billion years old, making them older than Earth. Today in the Proceedings of the National Academy of Sciences, the researchers report that they expected to find a 50:50 ratio of right- to left-handed amino acids in the rocks, but instead they found the ratio of amino acids tilted toward left-handedness in all six specimens. In one of the rocks, the imbalance was 18%, the largest ever reported for a meteorite. “I have to admit I didn’t believe it at first,” Glavin says.”
