Replies

Stanley L. Miller1, Harold C. Urey1 and J. Oró2 (1) Department of Chemistry, University of California, 92037 San Diego, La Jolla, California, USA (2) Departments of Biophysical Sciences and Chemistry, University of Houston, 77004, Texas, USA Summary The role and relative contributions of different forms of energy to the synthesis of amino acids and other organic compounds on the primitive earth, in the parent bodies or carbonaceous chondrites, and in the solar nebula are examined. A single source of energy or a single process would not account for all the organic compounds synthesized in the solar system. Electric discharges appear to produce amino acids more efficiently than other sources of energy and the composition of the synthesized amino acids is qualitatively and quantitatively similar to those found in the Murchison meteorite. Ultraviolet light is also likely to have played a major role in prebiotic synthesis. Although the energy in the sun's spectrum that can be absorbed by the major constituents of the primitive atmosphere is not large, reactive trace components such as H2S and formaldehyde absorb at longer wavelengths where greater amounts of energy are available and produce amino acids by reactions involving hot hydrogen atoms. The thermal reaction of CO + H2 + NH3 on Fischer-Tropsch catalysts generates intermediates that lead to amino acids and other organic compounds that have been found in meteorites. However, this synthesis appears to be less efficient than electric discharges and to require a special set of reaction conditions. It should be emphasized that after the reactive organic intermediates are generated by the above processes, the subsequent reactions which produce the more complet biochemical compounds are low temperature homogenous reactions occurring in an aqueous environment.

What is the point you are making? Stanley Miller concluded in 1998 that "a high temperature origin of life involving these compounds (RNA bases) are unlikely (Miller and Levy, "The stability of the RNA Base; Shapiro, "A Simpler Origin of LIfe."Miller further concluded in the same publication that of the four bases cytosine has the shortest half-life even at low temperatures and raises the possibility tha the 'GC pair' may not have been used in the first genetic material." Miller himself refuted his own early experimentation....his words, not mine.