Biological Implications of Organic Compounds in Comets

Abstract Organic chemicals — compounds that contain carbon — are the substance of life and pervade the universe. Is there a connection between comets, which are rich in prebiotic organics, and the origin of life? Current concepts of biomolecular evolution are first reviewed, including the important paradigm of catalytic RNA. At the very least, impacting comets appear to have supplied a substantial fraction of the volatile elements required for life shortly after the Earth formed. Some impacting material may even have survived chemically intact to directly provide necessary complex prebiotic organic chemicals. For life to originate and evolve in comets themselves, liquid H2O would be absolutely required: arguments for and against26Al radiogenic melting of cometary cores are presented. Cometary panspermia, if theoretically possible, is not necessary to explain the origin of life on Earth. The Halley spacecraft provide evidence against Earth-type microorganisms in this comet’s dust.