Force that moves plates
We have no doubt that the horizontal movement of plates is due to mantle flow teplogravitatsionnyh - convection. The energy source for these flows is the difference between the temperature of the central regions of the Earth, which have very high temperature (estimated core temperature of about 5000 ° C) and temperature on its surface. Heated in the central zones of the Earth's species expanded (see thermal expansion), their density decreases, and they pop up, giving place to drop-down cooler and therefore heavier masses have already given some of the heat the earth's crust. This process of heat transfer (as a result of floating-hot light of the masses and heavy-immersion cooler mass) is continuous, resulting in convective flows. These flows - the flow are closed on themselves and form a stable convective cells, consistent flow direction with adjacent cells. At the same time at the top of the cells within the substance is almost in a horizontal plane, and it is this part of the flow carries the plates in a horizontal direction with great force through huge viscosity of mantle material. If the mantle was quite fluid - the viscosity of the plastic mantle beneath the crust would be small (say, like water or so), then through a layer of such a substance with low viscosity, could not pass the transverse seismic waves. A crust would be fascinated by the flow of such a substance with a relatively small force. But thanks to high pressure at relatively low temperatures prevailing at the surface Mohorovicha and lower the viscosity of mantle material here is very large (so that the scale of years, the substance of the mantle fluid (the fluid), and the scale of seconds - hard).
The driving force of viscous mantle material directly under the bark is the elevation of the free surface of the mantle between the region of ascent and descent of convective flow field. This elevation, one might say, the deviation from isostasy, formed because of different densities slightly hotter (in the ascending part) and a little more than cold matter, because the weight of more and less warm poles in equilibrium is the same (with different densities!). In fact, the position of the free surface can not be measured, it can only be calculated (surface height Mohorovicha + height pillar mantle material, by weight of an equivalent layer of the lighter crust above the Mohorovicha).
The same driving force (drop height) determines the degree of horizontal compression of the elastic crust strength viscous flow of the earth's crust. The magnitude of this compression is low in the ascent of mantle flow and increases the closer to the place lowering the flow (through the transfer of compressive stresses through the fixed firm shell in the direction of the place of ascent to the place of descent of the flow). Above the drop-down flow of the force of compression in the crust is so great that from time to time exceeds the strength of the crust (in the lowest strength and the maximum voltage), is inelastic (plastic, brittle) deformation of the crust - an earthquake. In this place of crustal deformations extruded whole mountain ranges, such as the Himalayas (in several stages).
When the plastic (brittle) deformation is very fast (rate of displacement of the cortex during an earthquake) is reduced and the tension in it - the force of compression in the earthquake source and its surroundings. But immediately after the inelastic deformation continues, interrupted by an earthquake is very slow increase in tension (elastic strain) due to very slow as the motion of the viscous mantle flow, starting the cycle of the next earthquake.
Thus, the movement of plates - a consequence of heat transfer from the central zones of the Earth is very viscous magma. In this part of the thermal energy is transformed into mechanical work to overcome the frictional forces, and the portion passing through the Earth's crust, is emitted into the surrounding space. So that our planet is in some sense represents a heat engine.
The relatively high temperature causes the Earth's interior, there are several hypotheses. At the beginning of XX century was a popular hypothesis of the radioactive nature of this energy. She seemed to confirm the estimates of the upper crust, which showed a very significant concentrations of uranium, potassium and other radioactive elements, but later it became clear that the content of radioactive elements in crustal rocks is not sufficient to ensure that the observed flux of deep heat. And the content of radioactive elements in the subcrustal material (close in composition to basalts of the ocean floor), we can say, is negligible. However, this does not preclude a sufficiently high content of heavy radioactive elements that generate heat in the central zones of the planet.
Another model explains the heating of chemical differentiation of the Earth. Originally, the planet was a mixture of silica and metallic substances. But simultaneously with the formation of the planet began its differentiation into individual shells. A dense metal part rushed to the center of the planet, and silicates were concentrated in the upper shells. In this case the potential energy of the system is reduced and transformed into heat energy.
Other researchers believe that the warming of the planet is a result of accretion in collisions of meteorites on the surface of the nascent celestial body. This explanation is unlikely - if the accretion of heat is almost on the surface, where it easily took into space, rather than in the central region of the Earth.