A REVIEW OF CONDITIONS AFFECTING THE RADIOLYSIS DUE TO K-40 ON NUCLEIC-ACID BASES AND THEIR DERIVATIVES ADSORBED ON CLAY-MINERALS - IMPLICATIONS IN PREBIOTIC CHEMISTRY

This paper describes the possible effects of ionizing radiation arisin g from long-lived soluble radionuclides within clays, in particular K- 40, at the epoch of the emergence of life on Earth. The free dispersio n of soluble radionuclides constitutes an effective in situ irradiatio n mechanism that might have acted upon adsorbed nucleic bases and thei r derivatives on clays, inducing chemical changes on these organic mol ecules. Several types of well documented reactions for radiolysis of n ucleic acid bases and their derivatives are known, even at low doses ( i.e., 0.1 Gy). For example, estimates with a dose rate calculated from K-40 from deep sea clays at 3.8 Ga ago, indicates that over a period of 1000 years the amount of organic material transformated is 1.8 x 10 (-7) moles/kg-clay. Although ionizing radiation may also induce synthe tic reactions with prebiological interest, all in all these considerat ions indicate that nucleic acid bases and their derivatives adsorbed o n clays were exposed for long periods to degradation conditions. Such situation promotes decomposition of organic molecules rather than prot ection of them and enhancement of further polymerization, as it has be en usually taken for granted.