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Iron Meteorites and the Origin of Life: Phosphide Minerals on Early Earth and the RNA World.

Wednesday, May 18, 2005
Dante
Lauretta (UA Lunar and Planetary Lab)

Certain RNA sequences can both catalyze biochemical reactions, essentially playing a similar role to proteins in modern biochemistry, and store genetic information. These discoveries have led many researchers to support the RNA-world model where early life used RNA for both its catalytic and informational functions. This model requires several major steps to establish an RNA-world biotic system. The first step is synthesis of sugars, followed closely by formation of purine and pyramidine nucleoside bases. Then, nucleoside synthesis occurs by linking the sugars, preferably ribose, with the nucleoside bases. Phosphorylation of nucleosides then must occur in which the critical P-O-C bond sequence is formed linking a phosphate ion to the ribose molecule. Finally, long single-stranded polynucleotides are formed, some of which are then converted to complementary double strands by template-directed synthesis. Ultimately, one of these double-stranded polynucleotides had to be capable of separating and copying itself and its complement yielding a second ribozyme molecule. Repetition of this process would lead to an exponentially growing population, culminating in a system controlled by natural selection. I will present the results of an experimental study of aqueous corrosion of meteoritic phosphide minerals, common in iron meteorites, under conditions relevant to the early Earth. I draw three conclusions from this research: 1) aqueous corrosion of schreibersite produces many reactive P-bearing molecules; 2) these molecules readily phosphorylate organic species in solution; and 3) iron meteorites provided abundant reduced P to the early Earth and therefore should be considered in studies of the origin of life.

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