Watery Asteroids May Explain Why Life Is 'Left-Handed'

Image: Amino acids, such as isovaline (illustrated), come in left- and right-handed forms, but almost every living organism on Earth uses left-handed forms. New research suggests that water on asteroids amplified a bias - possibly caused by polarised starlight - towards left-handed amino acids (Illustration: NASA/Mary Pat Hrybyk-Keith)

From New Scientist:

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.

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