6. The Miller-Urey Experiment and Prebiotic Chemistry

Laboratory synthesis of a large variety of important prebiotic molecules is surprisingly straightforward, using conditions likely to apply to the early Earth. The variety of compounds formed with a reducing atmosphere is more diverse and amounts more abundant than when a CO₂ and N₂ is the starting point. Attempts to obtain useful amounts and types of prebiotic compounds starting from these more oxidized conditions typically require some method to add reducing capacity, which often seems somewhat ad hoc. Even if large amounts of prebiotic monomers can be produced, by whatever starting conditions, it is necessary to have mechanisms available to polymerize them to get useful biopolymers (polynucleotides and polypeptides). These polymerization reactions require dehydration, which may result from drying of some part of the prebiotic soup, or high temperatures associated with volcanism, or availability of specific active molecules such as polyphosphates. These requirements suggest that Darwin may have been correct in pointing to some kind of isolated surface pond loaded with suitable precursor compounds. Even if the early ocean was greatly enriched in organic compounds, as suggested by the degassing scenarios previously discussed, the mix of reaction conditions and energy available in a coastal setting with volcanism present seems a better bet for the emergence of life, than origin either in open water of even at deep-sea vents.