Cycles are a widespread feature of the geological processes. They are notable in rhythmic-bedded sedimentary rocks, volcanic formations, in the character of the explosive activity of a volcano and geyser, geotectonic cycles, fluctuations of glaciers, etc. The duration of cycles varies from minutes or hours (geysers) to many millions of years (geotectonic cycles). There are two types of cycles: (1) cycles caused by inner peculiarities of the system, and (2) cycles occurring as the result of external cyclic influences. For example, the cycles of the geyser activity are determined by the internal parameters of the system, but the rhythmic bedding of the varve is induced by the earth's rotation around the sun. The cycles of both types frequently interfere. The cycles of internal genesis are especially interesting, as they help to expose the specification of geological processes in connection with the specific feature of the very system. So, the invariable heat flow of the earth under certain conditions accompanied by melting of rocks is transformed into a pulsating one. The cycles of internal genesis appear when the components of the system essential non-linear alteration of its properties during the process. In this case the system itself begins to generate the oscillations. This regularity is of a general importance for different geological processes. The essence of the origin of cycles probably has the same basis in the animate and the unanimate nature. In the study of this basic principle, I see the great perspective of contacts between biologists and geologists dealing with problems of cycles.
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