[meteorite-list] Watery Asteroids May Explain Why Life is 'Left-Handed'

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 16 Mar 2009 17:23:36 -0700 (PDT)
Message-ID: <200903170023.RAA24294_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/article/dn16779-watery-asteroids-may-explain-why-life-is-lefth

Watery asteroids may explain why life is 'left-handed'
by Hazel Muir
New Scientist
March 16, 2009

Soggy rocks hurtling through the solar system gave life on Earth an
addiction to left-handed proteins, according to a new study. The
research suggests that water on asteroids amplified left-handed amino
acid molecules, making them dominate over their right-handed mirror images.

Curiously, almost every living organism on Earth uses left-handed amino
acids instead of their right-handed counterparts. In the 1990s,
scientists found that meteorites contain up to 15% more of the left
version too. That suggests space rocks bombarding the early Earth biased
its chemistry so that life used left-handed amino acids instead of right.

"Meteorites would have seeded the Earth with some of the prebiotic
compounds like amino acids that are needed to get life started, and also
biased the origin of life to the left-handed amino acid form," says
Daniel Glavin at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Some have suggested that polarised starlight preferentially destroyed
</article/dn7895-space-radiation-may-select-amino-acids-for-life.html>
right-handed amino acids on asteroids. But this alone couldn't explain
why the meteorite bias is so strong.

Now Glavin and colleague Jason Dworkin have shown that water amplified
the asymmetry.

They studied an amino acid called isovaline in six meteorites that
showed evidence of ancient exposure to liquid water for about 1000 to
10,000 years. The longer water persisted in the rock, the stronger its
left-handed isovaline bias, the team found.

Journal reference: Proceedings of the National Academy of Sciences (DOI:
10.1073/pnas.0811618106)
<http://www.pnas.org/cgi/doi/10.1073/pnas.0811618106>
Received on Mon 16 Mar 2009 08:23:36 PM PDT