Planetary Science Seminar
We argue that the emergence of life is an inevitable outcome of two particular disequilibria acting across the margins of a porous hydrothermal mound: (1) in redox potential, between hydrogen plus methane with the circuit-completing electron acceptors such as nitrate, ferric iron, and carbon dioxide, and (2) in pH gradient between an all-enveloping, mildly acidic, ocean and the alkaline hydrothermal fluid generating, and invading, the mound (Russell et al., 2014). The outer inorganic membrane separating the two fluids induces the gradients (Herschy et al., 2014). Both the CO2 in the ocean and the CH4 in the alkaline fluid were equally the ultimate sources of organic carbon. The metal sulfide (mackinawite, greigite and violarite) and oxyhydroxide (green rust) precipitates comprising the outer membrane have been shown to act as proto-enzymatic catalysts, as might be expected from their affinities with the active centers of their modern counterparts (Yamaguchi et al., 2014; Roldan et al., 2015). For example, mackinawite, greigite and violarite act as [Ni-Fe]-hydrogenase, CO dehydrogenase (CODH) and acetyl coenzyme-A synthase (ACS) (Huber and Wächtershäuser, 1997; Yamaguchi et al., 2014; Roldan et al., 2015) while green rust acts a nitrate and nitrite reductase, nitric oxide synthase, methane monooxygenase and methanol dehydrogenase, and possible as pyrophosphate synthetase (Barge et al., 2014).
Barge LM et al. 2014. Pyrophosphate synthesis… Geochim Cosmochim Acta 128:1-12.
Herschy B et al. 2014. An origin-of-life reactor to simulate alkaline hydrothermal vents. J Mol Evol 79:213-227.
Huber C, Wächtershäuser G, 1997. Activated acetic acid by carbon fixation on (Fe,Ni)S under primordial conditions. Science 276:245–247.
Roldan A et al. 2015. Bio-Inspired CO2 Conversion by Iron Sulfide Catalysts under Sustainable Conditions. Chem Comm DOI: 10.1039/C5CC02078
Russell MJ et al. 2014. The drive to life on wet and icy worlds. Astrobiology 14:308-343.
Yamaguchi A et al. 2014. Electrochemical CO2 reduction by Ni-containing iron sulfides: How Is CO2 Electrochemically Reduced at Bisulfide-Bearing Dee