Did life's bias come from space? More evidence

by Emily Chung

Like a pairs of gloves, the building blocks of proteins come in left-handed and right-handed versions that are exact mirror images of one another.

Just as your left foot only fits properly into a left shoe, living things interact with and produce only the "left-handed" version of those building blocks, which are called amino acids.

But if you make amino acids from scratch in a lab using their chemical components, you inevitably get half of the right-handed version and half of the left handed version.

So it might be expected that if nature makes amino acids in space using similar chemistry, you'd also get a fifty-fifty mixture.

Studies of individual meteorites have found that surprisingly, sometimes there can be quite a lot of "extra" left-handed amino acids on a meteorite. A new study published Monday in the Proceedings of the National Academy of Sciences confirms that's no fluke and suggests how that bias may have arisen.

The authors of the paper, Daniel Glavin and Jason Dworkin of the National Aeronautics and Space Administration Goddard Space Flight Center in Greenbelt, Maryland, found that three out the six meteorites that landed in Antarctica and that they studied, had significantly larger quantities of the left-handed version of the amino acids than the right-handed version. In fact, one had a whopping 18 per cent more of one particular amino acid.

Glavin and Dworkin suggested that such meteorites, asteroids, comets and their fragments may have delivered extra left-handed amino acids to the earth before life began and "biased" the Earth's inventory of organic compounds, encouraging living things to build themselves using the more readily available left-handed version.

The study used a different analysis technique than had been used by other studies, independently backing up the results of those previous studies.

The researchers also noticed a pattern -- only meteorites that were extensively altered by water while still attached to their parent asteroid have the large excess in left-handed amino acids.

"Therefore, water played a very important role in the bias of left over right handed amino acids in meteorites," Glavin said in an email.