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Project Progress

Environment of Prebiotic Earth and the Origin of Life (dm)

This year we essentially finished our planned experimental work on the fate of CO on an early Earth. We studied the kinetics of the hydration of CO and the fate of the hydration products.Formate decomposition is first order overall under anoxic, ambient pressure conditions. In neutral to alkaline solutions, pH is not a significant factor in the overall rate of formate decomposition, but as the pH approaches the pKa of formic acid, it becomes apparent that formic acid decays much more rapidly than formate. The decomposition product includes formaldehyde. The rate of the decomposition reaction is unaffected by the presence of minerals or dissolved metals. UV-C radiation accelerates the formate decomposition rate ~100-fold and promotes the formation of acetate, particularly in alkaline solution. Perhaps one of the more interesting results of this study in terms of prebiotic chemistry is the preservation of acetate in irradiated formate/FeCl2 solutions. The Fe(OH)3 precipitate is such an effective shield for acetate that the compound remained stable in UV-C, even after the formate concentration had been photolyzed. The 100microM FeII experimental concentrations simulate the levels in the Archean ocean at the time of banded iron formations.

We have also followed up on our discovery that hydrogen peroxide is produced in anoxic solutions through a reaction between water and pyrite. Subsequent experiments with a pyrite analog, NiS2, show the same effect. A mechanism involving defect sites on the surface of metal disulfides has been formulated. This finding may be of significance to local environments on the early Earth. Its presence may have been a driving force in the evolution to the oxygenic photosynthetic system.