A reassessment of prebiotic organic synthesis in neutral planetary atmospheres

The action of an electric discharge on reduced gas mixtures such as H(2)O, CH(4) and NH(3) (or N(2)) results in the production of several biologically important organic compounds including amino acids. However, it is now generally held that the early Earth's atmosphere was likely not reducing, but was dominated by N(2) and CO(2). The synthesis of organic compounds by the action of electric discharges on neutral gas mixtures has been shown to be much less efficient. We show here that contrary to previous reports, significant amounts of amino acids are produced from neutral gas mixtures. The low yields previously reported appear to be the outcome of oxidation of the organic compounds during hydrolytic workup by nitrite and nitrate produced in the reactions. The yield of amino acids is greatly increased when oxidation inhibitors, such as ferrous iron, are added prior to hydrolysis. Organic synthesis from neutral atmospheres may have depended on the oceanic availability of oxidation inhibitors as well as on the nature of the primitive atmosphere itself. The results reported here suggest that endogenous synthesis from neutral atmospheres may be more important than previously thought.