Photochemical survival principle in molecular evolution

The role of solar radiation in molecular evolution is considered. The evolutionary trend is toward utilization of longer wavelength photons. In this process the short wavelength (ultraviolet) photons become detrimental and a protective atmosphere is becoming a necessity. It is proposed that for evolution to proceed, a conservation relation must be satisfied between the constructive and destructive actions of solar radiation on the one hand and the relative rates of biological synthesis and destruction on the other hand. This conservation relation requires that the rate of photosynthesis by visible light exceeds the photodestruction by the short ultraviolet. The thickness and absorbing properties of a selective atmosphere and the ratio of the quantum yield of synthesis to that of destruction are the parameters entering the conservation relation. Calculations have been performed of the minimum atmosphere necessary for later periods of molecular evolution.