Why is life left-handed? Protein amino acids on Earth are almost entirely L-enantiomers, rather than right-handed D-enantiomers. When an excess of L-amino acids was discovered on the Murchison meteorite, it seemed that our chemical bias might have had an extraterrestrial origin; but then questions were raised about contamination of the samples. Now the extraterrestrial nature of this excess has been confirmed, re-igniting speculation that an astrophysical process of some sort decided our chemical handedness.
