ORGANIC-INORGANIC INTERACTIONS FOR THE CHEMICAL EVOLUTION OF LIFE ON THE EARLY EARTH

The chemical evolution process from simple molecules to polymers is thermodynamically difficult and need external energy. In order to overcome this difficulty, we propose here a new mechanism of coupled organic-inorganic evolution by using a spontaneous transformation of unstable inorganic materials (minerals) under hydrothermal conditions. If the Gibbs free energy change of reaction for organic transformation (polymerization) is +10 kJ/mol and that for mineral transformation is about –30 kJ/mol, the value for the combined organic-inorganic transformation becomes –20 kJ/mol, and the overall reaction can proceed. Several hydrothermal experiments for simulating the chemical evolution of life were conducted. The peptide formation rates from Glycine (Gly) to glycylglycine (GlyGly) were found to be much slower than the GlyGly decomposition rates. By adding silica gel, the GlyGly formation rate increased with increasing silica. Therefore, the presence of silica can favor the chemical evolution of amino acids to peptides. Hydroxyapatie (HAP) was found to affect the hydrothermal transformations of adenosine and ribose. HAP can be useful in the formation of RNA precursors. These organic-inorganic interactions might provide favorable environments for the first primitive life. The molecular signatures of the early life were also studied by IR and Raman microspectroscopies. Precambrian microfossils were found to contain C-N bonds in their graphite-like carbonaceous structures in less crystalline silica matrix. In-situ micro IR heating experiments of a Bactetia and an Eucarya indicated the remaining C-N bonds after the heating, in agreement with the above molecular remnants during the fossilization processes. All these studies will provide constraints for elucidating materials and mechanisms needed for the origin and evolution of life on the early Earth.