“If a verified non-terrestrial biological sample were ever found to use the same nucleobase set as terrestrial life (A/T/C/G), would you read that primarily as evidence for shared ancestry, convergent chemistry, or directed panspermia — and what single measurement do you think would most cleanly distinguish those possibilities?”
My reply was straightforward:
“It could either be a sign of shared ancestry or a universal path for life. But note that DNA/RNA chirality has a 50% chance of being right-handed as it is on Earth. This causes the double helix to twist exclusively to the right. Similarly, amino-acids are left-handed in all terrestrial lifeforms.
Hence, chirality will be a test of a common ancestry. If we study many extraterrestrial life samples and half of their double helix building blocks are left-handed, then we would know that they do not have a common ancestry, even if the nucleobase set is the same.”
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