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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. PDF
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