Hydrothermal vent organic synthesis

In the absence of oxygen and in the presence of H2, reduced carbon is thermodynamically preferred. That is certainly true deep in the ocean, for example, near hydrothermal vents, where the synthesis of reduced organic compounds is thermodynamically favored. Shock, Cody, and others have exploited that fact to propose net synthesis of organic molecules in anoxic environments.14,15... 

Unlike two previous theories of life origin, only a few pieces of experimental evidence exist at present to prove the theoretical speculations. However, we have to notice the verification of the basic mechanism of molecular hydrogen generation as a reducing power, furthermore, the amide bond synthesis has been also demonstrated, both at temperatures within the range of hydrothermal vents (100 °C). In addition, the evidence for at least sulfide-based amino acid synthesis and polymerization from simple precursors has been shown. The formation of acetic acid and an activated thioester from carbon monoxide, methanethiol and various combinations of ferrous and nickel sulfides has been experimentally proved as well. However, further verification is necessary for the modes and rates of organic synthesis. 

Particularly important here is the role of transition metal sulfides. In 1988 Wachtershauser proposed that pyrite, abundant in hydrothermal vent systems, provided an energy source for the first life. He suggested that pyrite provided the catalyst necessary to drive a number of essential chemical reactions which are important precursors to life. More recent studies have confirmed this view and have shown that the sulfides of Fe, Ni, Co, and Zn can play an important role in the fixation of carbon in a prebiotic world (Cody et al., 2004). Transition metal sulfides also play a role in more advance organic synthesis, and Huber and Wachtershauser (1998) showed how amino acids were converted into their peptides using a (NiFe)S catalyst. 

It is possible that inorganic cell prototypes were created in hydrothermal systems. Iron sulfides are abundant in oceanic hydrothermal systems and are one of the main products of high-temperature vents. Russell and Hall (1997) and Martin and Russell (2003) proposed that iron monosulfide bubbles, created in an oceanic hydrothermal setting formed a template for the structure of the first cells. In this model the FeS membrane acted as a catalytic chamber within which organic synthesis could take place. As this process evolved, the sulfide membrane became coated with abiotic organic polymers which eventually took over from the sulfide and replaced their function. 

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