Theoretical ideas based on the results of numerically modeling the mantle convection are presented. The thermochemical model accounts for such factors as a two-layer structure of the mantle, formation of light substance in the D'' layer (owing to transition of metallic components into the core), and heavy substances in subduction zones (eclogite-alteration of the oceanic crust). Numerical experiments have shown that this system allows phenomena of global mantle overturns, which makes possible to model the general pattern of the Earth's geologic evolution. The suggested theory establishes he cause-effect relationships in the sequence of geological events and is conformed by all the empirical data.
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