Reduction of nitrogen compounds in oceanic basement and its implications for HCN formation and abiotic organic synthesis |
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| Authors: | Nils G Holm Anna Neubeck |
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| Institution: | (1) Department of Geology and Geochemistry, Stockholm University, Stockholm, Sweden |
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| Abstract: | 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. 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, under alkaline conditions in hydrated mantle rocks of the overriding plate. Convergent margins in the
initial phase of subduction must, therefore, be considered the most potent sites for prebiotic reactions on Earth. This means
that origin of life processes are, perhaps, only possible on planets where some kind of plate tectonics occur. |
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| Keywords: | |
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