The Chemoautotrophic Origin of Life

The reaction affords a broad range of hydrocarbons and is normally carried out in a water-free medium. Since other conditions are valid for abiotic syntheses, the term FTT is used. 

The geological process of the formation of serpentine from peridotite probably involves the synthesis of carbon compounds under FTT conditions (see Sect. 7.2.3). The hydrogen set free in the serpentinisation process can react with CO2 or CO in various ways. The process must be quite complex, as CO2 and CO flow through the system of clefts and chasms in the oceanic crust and must thus pass by various mineral surfaces, at which catalytic processes as well as adsorption and desorption could occur. 

Horita and Berndt (1999) studied the abiogenic formation of methane under conditions present at hydrothermal vents. Solutions of bicarbonate (HCO3 ) were subjected to temperatures of 470-670 K and a pressure of 40 MPa. Under these conditions, CO2 was reduced only very slowly to methane. Addition of a nickel-iron alloy, which corresponds closely to the minerals in the Earth s crust, led to a clear increase in the reaction rate of methane synthesis. The following reaction is assumed to occur  

The yields of methane are directly proportional to the amount of alloy added. Abiotic methane formation is probably more general than had previously been thought, in particular since nickel-iron alloys have been found in the oceanic crust. 

Prebiotic chemistry must cope with many problems a particularly difficult one is contamination. Prebiotic experiments often lead to the formation of important molecular species in extremely low concentrations. The successes of the synthesis may sometimes appear sensational, but there is always the danger that artefacts may be involved. Control experiments carried out with ultrapure deionised water showed that, at higher temperatures ( 373 K), synthetic polymers in components of the apparatus could provide a source of organic contaminants such as formate, acetate or propionate ions. Stainless steel had a catalytic effect on the decomposition of formate, so that the use of titanium alloys in the apparatus is recommended. 

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The 21.3 reaction was assumed to be the energy source of the primordial initiation reaction for a chemoautotrophic origin of life. Huber and Wachtershauser [9] assumed that this reaction is initiated by the reductive formation of methyl mercaptan (CH3SH), its subsequent carbonylation to thioacetic acid (CH3COSH) and hydrolysis to acetic acid. The transition metal (Fe, Ni, Co) sulfides were assumed to be catalysts of formation of acetic acid by carbon fixation. 

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