Accordingly, we can imagine the magnitude of the fluctuations in the rotational regime of the Earth caused in the past by redistributions of the water masses on the Earth's surface. For example, during the Quaternary period, at the time of maximum glaciation, the level of the World Ocean may have been more than 130 to 150 meters lower than it is at present. Thus the diurnal-rotation regime of the Earth is largely a function of the climate.
The correctness of this conclusion is confirmed by certain factual data. Observations indicate that the secular accelerations of the average motions of the Sun and the Moon (and thus the secular changes in the rotational regime of the Earth) cannot be explained in terms of a single tidal mechanism. For the present epoch (the last 2000 to 2500 years), for example, a secular acceleration of the Earth's rotation must be assumed in addition to the secular tidal slowing down which is known to have taken place. This acceleration component of the change in the diurnal rotation can be assumed to be climatic in origin.
The following conclusions of Maksimov are noteworthy with respect to the relation between climate and the rotation of the Earth; "... the simultaneity of the changes in the rotational speed of the Earth which took place during the last centuries, on the one hand, and the changes in the main climatic characteristics of the polar regions, on the other, is an indubitable and very interesting fact. For the Arctic Ocean, in particular, it is especially significant that the changes in the Earth's rotational velocity were simultaneous with large-scale variations in the overall iciness of the polar seas. This fact in itself deserves a detailed study" (Maksimov, 1960, p. 14). "A simple comparison of the long-term variations in the Earth's rotational velocity with the index of atmospheric circulation and the circulation of the ocean in the Northern Hemisphere shows a definite relation between large-scale climatic changes and variations in the rotational velocity. The following two relations are important with respect to marine phenomena: the correlation between variations in the rotational velocity of the Earth and changes in the overall iciness of the Arctic Ocean; and the correlation between variations in the rotational velocity and long-term changes in the height of mean sea level in the northern parts of the Atlantic and Pacific Oceans" (Maksimov, 1960, p. 12). "The secular fluctuations (periods of 200 or 300 years) in
the iciness of the northern part of the Atlantic, in the continental quality of the climate of western Europe, and in the mean sea-level height of the Caspian Sea, during the last three centuries, were in phase with the variations in the rotational velocity of the Earth" (Maksimov, 1954, p. 75).
Now let us consider how tectonics depends on the diurnal-rotation regime. Any variation in the rotational velocity of the Earth will cause a regular change in the shape of the planet, so as to make it conform completely to the new rotational regime; as a result, gravitational equilibrium will be re-established. In other words, the world will pulsate along its diurnal-rotation axis, sometimes becoming more ellip soidal and sometimes becoming less ellipsoidal. As a result of these transformations of the planetary figure, various tectonic phenomena are produced, which serve as a unique means of relieving the excess physico mechanical stresses. These phenomena take place at the expense of the weakest crustal and subcrustal regions of the Earth*.
The Earth's crust, and perhaps part of the mantle as well, has a non uniform horizontal structure and consists of a great number of more or less rigid blocks which are joined together at comparatively weak regions [contacts]. Because of this, the localization and direction of dislocations will in general be determined by the dimensions, configurations, and strengths of the blocks, and also by the relative weakness of the regions of the Earth's crust located at the contacts between the blocks.
When the rotation of the Earth slows down, the shape of the planet becomes less ellipsoidal, because the centrifugal forces are smaller. Since for a body of given volume the sphere has the least surface area, the Earth will then appear to be in a contraction phase. Areas of the crustal layer will become redistributed, and there will be an efflux of subcrustal material from the equatorial bulge of the Earth toward the polar regions. Tectonic movements characteristic of a contracting surface of the Earth will take place in the crust, the movements being attenuated gradually with depth.