The parageneses thermodynamic analysis of chemoautotrophic CO 2 fixation archaic cycle components, their stability and self-organization in hydrothermal systems

Abstract

The parageneses physico-chemical analysis based on a method of thermodynamic potentials has been used to study the system of C–H–O organic compounds, which are, in particular, components of biomimetically built primordial cycles of carbon dioxide chemoautotrophic fixation. Thermodynamic data for aqueous organic compounds allowed one to construct the chemical potential diagrams and establish the areas of thermodynamic stability (facies) of components of CO 2 fixation pathways in hydrothermal systems, in particular, a reductive citric cycle (RCC), 3-hydroxypropionate cycle (3-HPC) and acetyl-CoA pathway. An alternative deep source of carbon (hydrocarbons) proved by the data on endogenous emission of hydrocarbons in hydrothermal fields of oceanic ridges was suggested. The system was determined, which combines hydrocarbons, CO 2 and components of RCC, 3-HPC and acetyl-CoA pathway with characteristic parageneses of methane and ethylene with acetate in two-component CH 4–CO 2 and C 2H 4–O 2 subsystems, respectively. The thermodynamic analysis of a redox mode at various pressures and temperatures allowed one to uniquely determine hydrocarbon–organic system able to independently generate acetate and succinate at oxidation of deep hydrothermal hydrocarbon fluids emerging on sea surface. The limits for thermodynamic stability of CO 2 archaic fixation (CAF) components responsible for generation and self-organization in hydrothermal environment was identified. The tentative integrated system of CAF was developed as a combined acetyl-CoA pathway, 3-HPC and RCC containing a succinate–fumarate core, capable of switching electron flow in forward or reverse direction depending on redox potential of geochemical environment that is governed by the (CH) 2(COOH) 2+H 2 (CH 2) 2(COOH) 2 reaction. This core is a “redox switch”, which is sensitive to certain conditions of hydrothermal environment and defines electron flow direction. The redox geochemical mode caused by temperature, pressure, composition of a hydrothermal fluid and a mineralogical setting defines stability of CAF cycle components in paragenesis with hydrocarbons and possibility of cycle self-organization.