Amino Acids Alter the Morphology of Hydrothermal Chimneys Composed of Iron Oxides and Oxyhydroxides

Science Center A154

Serpentinization of ultramafic crust at moderate temperatures produces an alkaline fluid which seeps into the ocean and reacts with dissolved metal cations to form hydrothermal chimneys. These hydrothermal chimneys catalyze organic synthesis using the electrochemical gradient between oxidizing, acidulous ocean and reducing, alkaline crust. We simulate a hydrothermal chimney that could have existed on the early Earth, Mars or on the icy moons of Jupiter and Saturn by anaerobically injecting sodium hydroxide into a reservoir of dissolved ferrous and ferric chloride. ESEM and Raman Spectroscopy show that our growing chimney simulants initially form hollow, porous, dark green stalks composed of layered iron oxides and oxyhydroxides, which are then coated on the exterior by orange iron oxyhydroxides. We show that when alanine is present in the alkaline injection solution, the resulting chimneys have weakened walls containing a widened range of crystal morphologies, including sharp plates and rounded disks. When cysteine is present in the injection solution, the resulting chimneys are weaker and more elastic than with alanine. This suggests that amino acids bind to chimneys via their amino-carboxyl backbones and, if applicable, via thiol groups. Our results support the theory that in the prebiotic evolution of early enzymes, amino acids could have interacted with mineral fragments from a hydrothermal chimney, ultimately forming protoenzymes with inorganic clusters from the chimney at their active centers.