The alkaline solution to the emergence of life

Michael J. Russell, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

Hydrogen dissolved in ~100 °C alkaline submarine springs was unstable with respect to the carbon dioxide dissolved from the ancient atmosphere in the 4.3 Ga ocean. But reaction between the two volatiles was strongly inhibited by kinetic barriers. One of these barriers was overcome during hydration and oxidation of the oceanic crust (serpentinization) in off-ridge alkaline hydrothermal convection cells. Here, H2 reacted with bicarbonate to produce formate (HCOO-), a first step in the reduction of carbon dioxide. On exhalation and mixing of this hot solution, now containing H2, NH3, HCOO- and HS- with the cool Fe2+-bearing carbonic ocean, metastable acetate (CH3COO-) was synthesized in a co-precipitating hydrothermal mound's natural hydrothermal reactor comprising freshly precipitated metal sulfides (e.g. Fe5NiS8) that catalyzed the reductions [1]. Such sulfides were later sequestered by short peptides to form the first enzymes that contain similar catalytic centres (e.g., Fe4NiS5) [2]. Thus the acetyl coenzyme-A metabolic pathway emerged; the likely first metabolic pathway of life. This pathway generates both energy and organic carbon for cell growth.

[1] Martin, W. and Russell M.J. 2007, Phil. Trans Royal Soc. London Ser. B DOI 10.1098/rstb.2002.1183.

[2] Milner-White, E.J., Russell, M.J. 2005, Origins Life Evolution Bios. 35, 19-27.