In its first stages this propagation of solidification may have been fully compensated by the increasing thickness of the molten layer in the downward direction. Subsequently this compensation must have been superseded by a gradual decrease in the thickness of the molten layer, the rate of its solidification on top being higher than the rate of the downward propagation of fusion. Finally, with further depletion of the radioactive elements, slow solidification must have taken place throughout the entire molten layer. Many Soviet and non-Soviet geophysicists contend — on the basis of the unimpeded propagation of transverse seismic waves throughout the entire shell, including the Earth's core — that this shell is now in the solid state and may contain only isolated molten "oases".
The possible existence of a molten layer in the outer portion of the Earth's shell in the recent geological past is consistent with geological observations that have revealed the following: 1) the extensive occurrence of magmatic chambers over the Earth and huge amounts of effluent lavas on the Earth's surface; 2) repeated intrusions and extrusions of magma in the same areas, often separated by considerable periods of time, of the order of magnitude of tens of millions of years, while the total duration of mag matic activity in these areas reached hundreds of millions of years.
According to Lyubimova, many geophysical observations seem to indicate the existence of a differentiated, molten layer with acid rocks concentrating in the outer portion and rocks with a higher content of iron having sunk toward the base. Simultaneously a redistribution of radioactive elements took place, with enrichment in the upper acid rocks and depletion in the lower strata. This must have increased the temperature gradient in the so-called waveguide layer whose presence has been established by geo physicists at a depth of about 150km (in strata with lower seismic wave velocity), and decreased the temperature gradient at the base of the "differentiation zone". The base of this zone coincides with the so-called "C-layer", with high seismic wave velocities and a jump in electrical conductivity, found by geophysicists to exist at depths of 600 to 900 km.
Lyubimova's calculations indicate that the temperature gradients are precisely those which are required for the observed variation in seismic wave velocities. According to Lyubimova, the concentration of iron due to the differentiation of matter in the lower portion of the molten layer (which she designated "differentiation zone") "is capable of increasing the electrical conductivity at these depths, analogous to the case of several 'silicate glasses which usually possess low ionic conductivity, but which acquire high electronic conductivity in the presence of iron impurities" (1958).
The fusion and subsequent solidification of a thick layer within the shell, which caused alternate extension and contraction of the Earth's radius, a protracted increase of the radius due to the thermal expansion of the inner portions of the Earth, as well as possible changes in the length of the radius due to other transformations of matter, inevitably generated deformations in the outer part of the shell. While ascribing due importance to variations in the physicochemical state of matter inside the Earth, it cannot be denied that variations in the Earth's rotation must have played an important part in the deformations of the outer portion of the shell. Variations in the Earth's volume (within limits) do not provide any convinc ing explanation for many characteristics of the deformations of the Earth's crust, such as their periodic formation and their geographical distribution.
Indeed, an explanation of the fairly regular periodic formation of exten sive folded structures requires the assumption of regular periodic variations in the liberation and accumulation of radiogenic heat inside the Earth, or of regular periodic variations in the outflow of heat toward the Earth's surface. However, such assumptions are improbable, since radioactive elements decay at a constant rate which is independent of temperature and pressure. The assumption of other cyclic variations in the state of matter, similar to harmonic oscillations, is also of low probability. Even if they did exist, it would be very difficult to provide a convincing explanation for the formation of extensive folded zones in certain geological periods being limited to the polar regions, with the equatorial regions being devoid of their age analogues. It is also difficult to explain why the formation of folded structures in the polar regions was accompanied by synchronous tensile deformations of the Earth's crust in the equatorial regions, accom panied by faults, nonuniform radial uplifts, and profuse fissure eruptions mainly of basic magma. For example, the Upper Carboniferous —Lower Permian folded structures of the Urals and the Upper Latians have neither direct continuations in equatorial regions nor submeridional age analogues. The extensive Upper Cretaceous—Lower Tertiary submeridional folded structures of northeastern USSR and of the Rocky Mountains of North America similarly have neither a direct continuation nor age analogues in the equatorial regions.