HR: 15:10h
AN: U43B-04 INVITED     [Abstracts]
TI: Planetary Differentiation and the Emergence of Life
AU: * Shock, E L
EM: eshock@asu.edu
AF: GEOPIG, Depts. of Geological Sciences and Chemistry & Biochemistry Arizona State University, Tempe, AZ 85287 United States
AB: Organisms use energy from light, chemical reactions, or both. The use of chemical energy apparently pre-dates the use of light, and forms the foundation of all subsurface and high-temperature ecosystems. Therefore, the emergence of life seems linked to the availability of chemical energy in the Earth's crust. Chemical energy sources exist because many of the materials composing the habitable volume of the Earth formed at higher temperatures, and are out of oxidation/reduction equilibrium with their cooler surroundings. At extreme temperatures, such as those that prevail in the mantle or in magmatic systems, many processes occur in response to shifting equilibria, with little to no inhibition from kinetic barriers. However, differentiation processes allow materials to migrate and to become segregated, with direct consequences for the development of disequilibrium states. As an example, recently-formed melt in the upper mantle is far closer to equilibrium with its surroundings than is the resulting solidified basaltic lava at the surface. One reason is the steep temperature dependence of the rates of oxidation/reduction reactions. Redox disequilibria develop as materials cool through the 400 to $200\deg$C range, depending on the chemical system. As temperatures drop, redox reaction rates become so slow that they converge on geologic time. These redox disequilibria form the chemical energy supplies used by life, which catalyzes favorable but sluggish reactions to drive metabolic processes, lowering the energy state of the total system. It follows that life continues the release of energy begun by planetary differentiation but stalled by sluggish oxidation/reduction reactions. In this sense, life is inevitable, as it greatly enhances the efficiency of reactions that release energy, which would otherwise not proceed in its absence. Therefore, understanding the emergence of life relies on our ability to conceptualize the initiation of catalysis in systems that are rich in redox disequilibria. Processes that focus and juxtapose redox disequilibria are likely crucibles for the emergence of catalysis and life. In particular, the flow of aqueous fluids through diverse products of differentiation may engender the necessary gradients.
DE: 8125 Evolution of the Earth
DE: 5455 Origin and evolution
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 0400 Biogeosciences
SC: Union [U]
MN: 2004 AGU Fall Meeting