Sobotovich, E.V., Florinsky, I.V., Lysenko, O.B., and Grodzinsky, D.M., 2010. Role of isotopes in the biosphere. In: Florinsky, I.V. (Ed.), Man and the Geosphere. Nova Science Publishers, New York, pp. 33–68.
This chapter consists of two main parts. The first deals with the phenomenon of biological fractionation of stable isotopes as a contribution to isotopic fractionation in geological processes. The second deals with biological roles of natural radioisotopes. We briefly address kinetic, thermodynamic, and magnetic isotope effects. Fractionation of stable isotopes of some biogenic elements (H, C, O, N, Mg, S, K, Ca, Fe, Cu, and Zn) in the human body is discussed. In particular, we consider (a) the natural isotopic composition of human tissues, fluids, and gases including the temporal dynamics of those isotopic compositions; (b) impacts of diet and geographical peculiarities on human isotopic composition; and (c) dependence of human isotope ratios on the state of health and age. We suppose that each living organism and each of its systems can be characterized by a typical isotopic composition, “an isotopic signature”, which is related to the environment. In the signature, typical isotope ratios may fluctuate supporting the state of isotopic homeostasis, a part of the general homeostasis of the organism. There are also sharp changes in typical isotope ratios exceeding the ranges of such fluctuations. Sharp isotope shifts may be used as natural internal markers of pathological processes.
Finally, we address biological effects of natural radioisotopes and their role in speciation and biological evolution. Experimental studies testify that natural background radiation is an important factor for the vital activity of organisms. Paleontological data suggest that dramatic periods of speciation and diversification have regularly occurred in periods of high natural radioactivity of the environment associated with the deposition of uranium-rich sediments. Within the East African Rift, a combined impact of regional geological processes has formed a zone of increased natural radiation that is suggested to have played a principal role in the origin of Homo sapiens. Possible mutagenic effects of the cosmic radiation increased during geomagnetic reversals and excursions are also discussed. We suggest that natural low dose ionizing radiation may be deleterious to individuals but beneficial for the population being one of the key factors generating variations that are acted upon by natural selection.