Solidification of the molten layer in the shell must have caused crustal compressive deformations of submeridional strike extending from the North to the South Pole, such as in the shape of stepped folded structures, as well as sublatitudinal folded zones around the entire Earth. Such structures could not have been missed by geological observations even if they re presented only marginal formations around intact crust fragments which had not undergone compressive deformations.
The contraction of the Earth's surface caused by the contraction of its volume and, consequently, of its radii, must be accompanied by a simul taneous decrease in the length of parallels and meridians.
Great difficulties are encountered in attempts to explain, with the aid of assumed variations in the Earth's state of aggregation, the possibility and cause of the formation, during the same geological periods, of com pressive deformations in the polar regions and of tensile deformations in the equatorial regions. However, this actually happened in the Upper Cretaceous—Lower Tertiary period when folding occurred in northeastern Eurasia and in North America, while India, Africa, and the Indian Ocean bottom were undergoing tensile deformations accompanied by the formation of numerous vertical or near-vertical faults obviously caused by tensile, rather than compressive stresses in the crust; tremendous extrusions of magma flowed from the fissures formed by these faults.
It is impossible to provide a plausible explanation of the alternating expansion and compression of the crust in the same fragment based solely on the physicochemical changes in matter. Alternations of this kind are known, for example, in the northeastern regions of the USSR and in the North-American Rocky Mountains. During the Triassic, Jurassic, and Lower Cretaceous periods the Earth's crust in these regions underwent tensile deformations accompanied by the formation of numerous long, steeply inclined, and even vertical faults of submeridional strike with intrusions and eruptions of magma mostly of basic and intermediate composition. In the Upper Cretaceous the same regions underwent folding processes which were, in turn, superseeded by tensile processes in later periods, including the Quaternary; these tensile deformations caused faults accompanied by differentiated radial uplifting of crust blocks and by fissure eruptions of magma. The difficulties involved in interpreting the
causes of the above events are eliminated by assuming that the crustal deformations were caused by the simultaneous effect on the crust of deforming forces generated by physicochemical changes in the matter, and by long-period variations in the Earth's rotation.
At the present time three types of variations in the Earth's rotational velocity are reliably known (Pariiskii, 1954). These are long-period (secular) variations, short-period variations (which include variations with cycles of 24 hours, half a year, a year and 14 months), and irregular discontinuous variations.
The tensile or compressive stresses generated in the shell by the short-period and the irregular variations in the Earth's rotation are much less than the tensile or compressive strength, and consequently they do not produce irreversible deformations of the Earth's crust; therefore we are not concerned with them. On the other hand, long-period variations in the Earth's rotation may cause the buildup of compressive and tensile stresses in the outer part of its shell, exceeding the tensile and compressive strength of the latter and generating irreversible deformations. We shall examine these variations more closely.
Comparison of observations of solar eclipses in ancient times performed by Greek, Babylonian, Chinese, and Egyptian astronomers with modern astronomic calculations reveals beyond doubt a decrease in the angular velocity of the Earth's rotation over the last 2000 years, as a result of tidal friction. Furthermore, it has been established by several scientists that the deceleration of the Earth's rotation is subtracted from its accelera tion; the latter is due to physicochemical variations of matter inside the Earth, and is therefore unrelated to tidal friction. In the USSR this problem was thoroughly investigated by Pariiskii (1945, 1948, 1953, and 1954), who demonstrated that the deceleration of the Earth's rotation over the last 2000 years due to tidal friction resulted in an average increase in the diurnal period of sec/year. This increment comprises an increase of 33 sec/year due to the deceleration caused by tidal friction, and a decrease of 1 sec/year which is obviously due to physicochemical variations of matter inside the Earth.