Reduction of oxidized nitrogen compounds during serpentinization of mafic rocks and prebiotic formation of early life molecules

Hydrogen cyanide is an excellent organic reagent and is central to most of the reaction pathways leading to abiotic formation of simple organic compounds containing nitrogen, such as amino acids, purines and pyrimidines. Reduced carbon and nitrogen precursor compounds for the synthesis of HCN may be formed under off-axis hydrothermal conditions in oceanic lithosphere in the presence of native Fe and Ni and are adsorbed on authigenic layer silicates and zeolites. The native metals as well as the molecular hydrogen reducing CO2 to CO/CH4 and NO3-/NO2- to NH3/NH4+ are a result of serpentinization of mafic rocks. Oceanic plates are conveyor belts of reduced carbon and nitrogen compounds from the off-axis hydrothermal environments to the subduction zones, where compaction, dehydration, desiccation and diagenetic reactions affect the organic precursors [1]. CO/CH4 and NH3/NH4+ in fluids distilled out of layer silicates and zeolites in the subducting plate at an early stage of subduction will react upon heating and form HCN, which is then available for further organic reactions to, for instance, carbohydrates, nucleosides or even nucleotides due to phosphorylation by pyrophosphate under the alkaline conditions prevalent in hydrated mantle rocks of the overriding plate [2]. Convergent margins in the initial phase of subduction must, therefore, be considered the most potent sites for prebiotic organic reactions on Earth. This means that processes leading to the origin of life probably are possible only on planets where some kind of plate tectonics occurs. References: [1] Holm N. G. and Neubeck A. (2009) Geochem T, 10:9. [2] Holm N. G., Dumont M., Ivarsson M., and Konn C. (2006) Geochem T, 7:7.