Reactions depending on iron sulfide and linking geochemistry with biochemistry.

Iron sulfide gives rise to unusual reducing reactions: some dependent on FeS/H2S synergism [NO-3 --> NH3; HC(three bonds)CH--> H2C=CH2, H3C-CH3; -CH2-CO- --> -CH=CH-, -CH2-CH2-; HS-CH2-COOH --> CH3-COOH; others dependent on FeS alone [HS-CH2-CH2-X --> CH2=CH2 (where X = OH, SH, or NH2)]. The experimental conditions are geochemically plausible: 100 degrees C, aqueous, nearly neutral, and fastidiously anaerobic. These reactions establish additional facts of soil chemistry, organic geochemistry, and the global nitrogen cycle. Further, they point to the common evolutionary denominator of geochemistry and biochemistry.