Birth of biomolecules from the warm wet sheets of clays near spreading centers

Abstract

The role of clay minerals in the abiotic synthesis of organic molecules near seafloor spreading centers was simulated experimentally. Clays are common hydrothermal alteration products of volcanic glass and due to their nano-scale crystal size, provide extensive and variably charged surfaces that interact with aqueous organic species. Volcanic gases H2 and CO2 have been shown to react on magnetite surfaces to form methanol, a primary organic molecule, under hydrothermal conditions. Therefore, our experiments simulated the temperature and pressure conditions (300°C, 100 MPa) that exist beneath hydrothermal vents, in stockwork fractures through which hydrothermal fluids interact with fresh basalt. We examined the products of reactions between aqueous methanol and three common clay minerals found in those environments (montmorillonite, saponite, illite). Montmorillonite reacted to ~60% illite over 6 weeks, while saponite and illite were mineralogically stable. Organic products extracted with dichloromethane from the two expandable smectite clays (montmorillonite, saponite) contained a variety of complex organic molecules including: alkanes, alkyl-benzenes, alkyl-naphthalenes, alkyl-phenols, alkyl-naphthols, alkyl-anthrols, methoxy and alkyl-methoxy-phenols, methoxy and alkyl-methoxy-naphthols, and long-chain methyl esters. Experiments with the non-expandable illite yielded only traces of alkanes and alkyl-benzene after 6 weeks. We infer that the interlayer surfaces of smectites provide crystallographic sites involved in the organic synthesis of polycyclic aromatic hydrocarbons. The largest variety and quantity of organic products was produced from montmorilloniteas the layer charge increased during conversion to illite.