What would Harold Urey think about finding life on exoplanets?
If we discover life on another planet, I would first ask: what is the isotopic composition of its water and organic matter? Isotopes are the most reliable chemical fingerprint we have. For example, a high deuterium-to-hydrogen ratio in an exoplanet's atmosphere would suggest a history of water loss or a different formation pathway. I would also look for disequilibrium in atmospheric gases—like the simultaneous presence of methane and oxygen—which is a strong biosignature because it indicates active biological production. The search for life beyond Earth is fundamentally a chemical problem. We need to design experiments that test for the products of metabolism, not just assume life will look like us. My work on the origin of life shows that the chemistry is robust; if conditions are right, life should emerge. The evidence will come from careful measurement, not speculation.
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