Ultraviolet light would have destroyed important prebiotic compounds.
Direct exposure to unattenuated ultraviolet light destroys amino acids and nucleic acid bases. Some creationists argue that this rules out a natural origin of life altogether, since the early Earth did not have an ozone layer to screen out ultraviolet light. Other creationists are more restrained, arguing that it rules out only a contribution to the origin of life by prebiotic synthesis in certain specific contexts.
I. Deep water
If the origin of life occurred near deep-sea hydrothermal vents, as one hypothesis proposes, it would have occurred at depths where ultraviolet light does not penetrate.
II. Medium-depth to shallow water
According to Cleaves and Miller (1998) a number of things could have protected prebiotic compounds in the early oceans at medium or shallow depths:
Cleaves and Miller (1998) conclude:
This analysis shows that there would have been a wide variety of both organic and inorganic UV absorbers in the primitive ocean that would have protected the UV-sensitive organic compounds such as the purines and pyrimidines, with amino acids being protected effectively by aqueous salts. Our models suggest that it is entirely possible that incident UV flux could have been attenuated to minimal intensities after passage through as little as 2 mm of ocean water (<1% T at 218 nm and 260 nm).
We recognize that any one of these concentration estimates may be in considerable error. However, entirely removing any one of the absorbers still leaves a variety of alternative absorbers that still would offer adequate protection.
Ultraviolet radiation does not even rule out a role for prebiotic synthesis in space. We know this because important prebiotic compounds have been detected in space; for instance, one team has detected the amino acid glycine in interstellar clouds (Kuan 2003).
Cleaves HJ and Miller SL. 1998. Oceanic protection of prebiotic organic compounds from UV radiation. Proc. Natl. Acad. Sci. USA 95:7260-7263.
Kuan Y-J et al. 2003. Interstellar glycine. The Astrophysical Journal 593:848-867.
Last update: 15 Jan 2015
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