# The Earth's structure

Much of what the previous generations have discovered, we take for granted, without thinking about the essence and meaning of these things. Every day from birth, our body experiences the gravity of the Earth, only after death, freed from its shackles, the free soul moves to a parallel world where it finds eternity. Probably, there, in the parallel world, there is no gravitation, souls are not material, it is possible on the contrary. One way or another - time will judge. But we know for sure that the Earth is inhomogeneous in its structure, and the Earth's structure still causes controversy among scientists and, accordingly, the emergence of various hypotheses about it. Today, tracing a simple chain of models of the device of the planet Earth, we will try to find a new one, something that has escaped the eyes of researchers and scientists.

Since Newton in the book of his third "Beginnings" formulated the law of gravity, according to which every particle in Universe attracts every other particle with a force back" proportional to some amount of matter that they contain, "gravity has come to be regarded as a universal property of matter. The fact that the gravitational force is proportional to the mass of the attracting body, Newton derived from the experimental fact, based on how Jupiter affects its satellites. The sun is affecting the planets, Earth - on Moon and the bodies on its surface in such a way that their acceleration equal to the distances from the corresponding central body. In this case, from the principle of equality of action and counteraction of forces, it follows that this force is proportional to the mass of the central body as well. Newton's law remains valid for material bodies whose dimensions are very small in comparison with the mutual distance. However, far from all the cases, the distance between the attracting bodies is large in comparison with their dimensions.

Consider, for example, the attraction of the Earth by a small material body located near its surface. In this case, the very concept of the distance between the Earth and the body becomes uncertain: we can talk about the distance to the nearest point of the Earth's surface, to the center of the Earth. If we mentally break the Earth into small particles with equal masses, these particles will attract the body we took with different forces. What law will the total gravity of the Earth obey if every particle of the Earth attracts inversely proportional to the square of the distance of the body before it? This question was first raised and solved by Newton. He proved a theorem according to which a homogeneous sphere consisting of particles attracting inversely proportional to the square of the distance attracts other material bodies to them and is attracted to them in the same way as one material particle placed in the center of the sphere and concentrating the whole mass of the ball in itself. This theorem also holds for an inhomogeneous ball consisting of spherical layers of equal density, that is, a sphere with a spherical distribution of densities.

Of course, not all bodies have a spherical shape, and not in all cases the distances between the attracting bodies are large in comparison with their dimensions. In this case, the law of force variation with distance will be more complicated.

Earth form is described by a figure called a geoid. The geoid is very close in shape to the ellipsoid with a slight contraction (1:298), which indicates that the substance of the planet is in hydrostatic equilibrium with respect to the acting forces of attraction and centrifugal inertia and behaves towards long-acting forces like liquid body. At the same time, short-term effects (elastic waves of earthquakes, tides and mass movements in Earth's atmosphere, which cause short-period pole movements) are perceived by the globe as a solid elastic body, the rigidity of which exceeds the hardness of hardened steel. Such a different reaction of the Earth to the effects of short and long periods indicates that the globe is an elastic-viscous body, the period of adaptation (relaxation) which is estimated several centuries.

Not only the external form of the Earth, but also the location of concentric layers of different density within it, are subject to the law of hydrostatic equilibrium, so that the globe, as it were, consists of a multitude of spheroidal layers that differ from one another in their physical state. These layers are arranged concentrically, so that the Earth is a spheroidal layered body. The average density of the Earth (5,52 g/cm3) almost twice exceeds the density of rocks composing the earth's crust, therefore, the density of the deep layers of the Earth is much greater. The density distribution within the Earth can be estimated, considering the mass and moment of inertia of the globe, as well as taking into account the data of studying the propagation of elastic waves of earthquakes.

The propagation of seismic vibrations indicates that the elastic properties inside the Earth change at certain certain depths (boundaries) abruptly and smoothly within the layers separated by these boundaries. The most important boundaries are the Mohorovich surface, lying at a depth of 10-70 km, and the boundary at a depth of 2900 km, which sharply refracts longitudinal seismic waves and does not allow transverse vibrations. The latter boundary is sometimes called the Wiechert-Gutenberg surface. These boundaries divide the globe into three main zones: the core, the shell and the crust. The Earth's crust has the greatest rigidity and is sometimes called the sclerosphere, that is, the hard sphere of the Earth. The shell has a higher viscosity; sometimes its outer layers are called asthenosphere, which expresses its compliance to external influences. The Earth's core is in a state close to liquid, and reacts only to longitudinal waves by changing its volume. Inside the three main zones of the globe there are less clearly defined interfaces, not always traceable to earthquake observations, but detected by more detailed analysis of seismological data. The shell, apparently, is dismembered at a depth of 1200 km by the Repetti boundary on the inner and outer layers. Seismological data also indicate other elastic boundaries in the shell, but their existence is not firmly established. The core of the Earth is divided into an inner core and an outer core, and the distance separating their boundaries from the center of the Earth is about 1250 km.

As you can see, everything is simple and the structure of the Earth seems more or less precisely fixed. Above the bark, on which we live, inside the layers with a sharp change in density during the transition from the shell to the core.

You can clarify what you read. It is possible to put forward new hypotheses of the device of the Earth, but, unfortunately, it is impossible to drill a well to the center of the Earth to refute or confirm them. Therefore, even models in which the laws of the device of the Earth lie not inside, but far beyond its limits deserve attention.

Author of the article: Alexander Babaskin

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