quote:
Chirality suggests to me a single origin of life, rather than a multi-regional outbreak. But it suggests nothing about where that single origin occurred. If it happened extra-terrestrially and migrated to Earth, then we are caught by Mr Jack's assertion that organic molecules with chirality couldn't survive a panspermatic impact.
On the other hand, a rare survival can't be ruled out, given what little we know about abiogenesis.
”HM
Life as we know it uses only left-handed amino acids. If you had a bunch of right-handed amino acids tossed into the mix it'd be much, much, much harder for proteins made from purely left-handed amino acids to arise. So a primordial earth couldn't have a collection of amino acids that was a decent mixture of left and right-handed amino acids.
Also, why in the world are people bringing up asteroid impacts? Not everything that falls to the earth are large, solid masses. The most likely explanation is an accretion of interstellar dust earlier in Earth's history, when planets were still mopping up remaining residues.