Reducing atmosphere, prebiotic synthesis

For these reasons, it is generally felt that the interstellar molecules played at most a minor role in the origin of life. However, the presence of so many molecules of prebiotic importance in interstellar space, combined with the fact that their synthesis must differ from that on the primitive earth where the conditions were very different, indicates that some molecules are particularly easily synthesized when radicals and ions recombine. Another way of saying this is that there appears to be a universal organic chemistry, which shows up in interstellar space, in the atmospheres of the major planets, and in the reducing atmosphere of the primitive earth. 

H2. The H2 would diffuse out of Earth s atmosphere. Even in these less reducing atmospheres (e.g., CO and CO2 instead of CH4, N2 instead of NH3), Miller-type experiments yield amino acids, nucleic acid bases, and simple sugars. However, such syntheses do not occur in the presence of molecular oxygen (O2) and the principle holds prebiotic synthesis requires a reducing atmosphere and is not possible in Earth s current oxidizing atmosphere. 

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