IONIZING RADIATION AND THE LONG-TERM SURVIVAL OF BIOMOLECULES AND VIABLE BACTERIA

Claims for the long-term survival of biomolecules and viable organisms in terrestrial deposits require consideration of the survival limitations imposed by the naturally occurring ionizing radiation associated with the decay of radionuclides. This process and its role in the preservation of biomolecules has not been adequately addressed in the past. Thus, we have investigated the effect of ionizing radiation on the survival of amino acids and different bacterial spores. For amino acids, even in the absence of thermal-induced decomposition, radiolytic degradation induced by the decay of U, Th and K limits their survival in most geochemical environments to less than a few 10's of millions of years. Radiolysis scales with molecular weight (the higher the molecular weight the larger the radiolysis degradation constant), thus molecules such as proteins and nucleic acids would be degraded even faster. With respect to geochemical samples, amber may be an ideal material because of the low levels of radionuclides in the matrix. For B. subtilis and S. marismortui spores in solution as well as for dry spores of B. subtilis and B. thuringiensis, radiolytic inactivation constants indicate that ionizing radiation in geological environments limits the survival of viable bacterial spores over long geologic periods. In the absence of active repair mechanisms, in the dormant state the long-term survival of spores is limited to less than ~100 million years in halite fluid inclusions and to several million years in sediments, fossil bones and shells. These results clearly need to be considered in any reports of either ancient amino acids or viable bacterial spores in various natural samples.