SOME REGULARITIES IN THE EVOLUTION OF THE EARTH Two more or less "universal" factors are usually cited as being responsible for many phenomena and facts related to the evolution of the Earth during the course of geological history. These two factors are climatic changes and tectonic movements. However, no really satisfactory theory has as yet been worked out which enables us to understand these factors, the result being that the corresponding phenomena and facts are very often explained vaguely, unconvincingly, or simply falsely.
In the present article we shall consider a third, very important, factor influencing the evolution of the Earth: the long-period fluctuations in the regime of its diurnal rotation. Essentially, the problem can be formulated as follows: the three factors (climate, diurnal-rotation regime, and tectonics) are mutually related and influence one another in a complex way. A variation in any one of these factors, whatever its cause may be, inevitably entails corresponding variations in each of the others, and many important characteristics of the Earth's evolution are determined by the interaction of these three main determining factors.
How is this relation between climate, diurnal-rotation regime, and tectonics actually effected? What is the mechanism of the interaction between these three factors? Finally, how are these factors related to the many other factors affecting the evolution of the Earth? First of all, let us discuss briefly the climate of our planet. Theory, observation, and the results of various studies all show convincingly that the continual recurrence of warm and cold periods is a general character istic of the Earth's evolution. This recurrence is apparently due to both terrestrial and extraterrestrial causes. An entire spectrum of cyclical fluctuations with smaller periods and amplitudes is superimposed onto the cyclical fluctuations whose periods and amplitudes are comparatively large. Observations also indicate that fluctuations in climate, long-term as well as short-term, have the same phase in both the Northern and Southern Hemispheres.
From the point of view of philosophy, "it is impossible to assume that the climate does not change, since everything in nature evolves and passes from one qualitative state to another" (Kalesnik, 1957). The following factors all vary during the course of time: the amount of heat transferred from the interior of the Earth to its surface; the energy radiating capacities of extraterrestrial bodies; the physical properties of the medium occupying the space between the Earth's surface and energy-radiating extraterrestrial bodies; the albedo of the Earth; the general planetary shape of the Earth; and the vertical-horizontal ratio between water and dry land, which determines the nature of the hydro atmospheric circulation. Consequently, the climate, which is affected by
all these factors, must vary with time as well. The variations in some climatogenic factors (or even in all the factors taken together) may appear to be irreversible at the end of a quite long period of time, but within the period itself these variations will have the nature of fluctuations.
As a direct result of the climatic changes, the water mass on the surface of the Earth undergoes periodic redistributions relative to the poles and the equator (that is, relative to the rotation axis). Thus, once a shoreline appeared (or, in other words, once the separation of the Earth's surface into dry land and water was completed), the presence of water in the solid state became possible. Accordingly, in many instances the natural conditions were such that snow, firn, and ice accumulated (or melted) to some extent or other, mostly in the high latitudes (around the poles) but also in the low latitudes (around the equator).
Such redistributions of the mass of the Earth alter the moment of inertia of the planet, and thus (since the product JW remains constant) its angular velocity as well. For example, if 3.2 cm of the ice cover of Antarctica melts during the summer, part of the water which is formed thereby will flow toward the equator. If this water were distributed uniformly over the surface of the sea, it would form a layer 0.12 cm thick. Such a small elevation of the water surface at the equator would naturally be difficult to observe directly, but even this minute change in the level of the sea would affect the velocity of rotation of the Earth. If this same change took place during 100 successive years, the rotation of the Earth would slow down by 18 seconds. A cold winter, on the other hand, causing accumulation of ice at the poles, has just the opposite effect: it makes the Earth rotate faster.