THE EMERGENCE OF LIFE FROM IRON MONOSULFIDE BUBBLES AT A SUBMARINE HYDROTHERMAL REDOX AND PH FRONT

Here we argue that life emerged on Earth From a redox and pH front at c. 4.2 Ga. This front occurred where hot(c. 150 degrees C), extremely reduced, alkaline, bisulphide-bearing, submarine seepage waters interf aced with the acid, warm (c. 90 degrees C), iron-bearing Hadean ocean. The low pH of the ocean was imparted by the ten bars of CO2 considere d to dominate the Hadean atmosphere/hydrosphere. Disequilibrium betwee n the two solutions was maintained by the spontaneous precipitation of a colloidal FeS membrane. Iron monosulphide bubbles comprising this m embrane were inflated by the hydrothermal solution upon sulphide mound s at the seepage sites. Our hypothesis is that the FeS membrane, laced with nickel, acted as a semipermeable catalytic boundary between the two fluids, encouraging synthesis of organic anions by hydrogenation a nd carboxylation of hydrothermal organic primers. The ocean provided c arbonate, phosphate, iron, nickel and protons; the hydrothermal soluti on was the source of ammonia, acetate. HS-, H-2 and tungsten, as well as minor concentrations of organic sulphides and perhaps cyanide and a cetaldehyde. The mean redox potential (Delta Eh) across the membrane, with the energy to drive synthesis, would have approximated to 300 mil livolts. The generation of organic anions would have led to an increas e in osmotic pressure within the FeS bubbles. Thus osmotic pressure co uld take over from hydraulic pressure as the driving force for distens ion, budding and reproduction of the bubbles. Condensation of the orga nic molecules to polymers, particularly organic sulphides, was driven by pyrophosphate hydrolysis. Regeneration of pyrophosphate from the mo nophosphate in the membrane was facilitated by protons contributed fro m the Hadean ocean. This was the first use by a metabolizing system of protonmotive force (driven by natural Delta pH) which also would have amounted to c. 300 millivolts. Protonmotive force is the universal en ergy transduction mechanism of life. Taken together with the redox pot ential across the membrane, the total electrochemical and chemical ene rgy available for protometabolism amounted to a continuous supply at m ore than half a volt. The role of the iron sulphide membrane in keepin g the two solutions separated was appropriated by the newly synthesize d organic sulphide polymers. This organic take-over of the membrane ma terial led to the miniaturization of the metabolizing system. Informat ion systems to govern replication could have developed penecontemporan eously in this same milieu. But iron, sulphur and phosphate, inorganic components of earliest life, continued to be involved in metabolism.