The Earth's mantle is part of the geosphere, locatedbetween the core and the core. It contains a large proportion of the total matter of the planet. The study of mantle is important not only from the point of view of understanding the internal structure of the Earth. It can shed light on the formation of the planet, give access to rare compounds and rocks, help understand the mechanism of earthquakes and movement of lithospheric plates. However, it is not easy to obtain information on the composition and features of the mantle. So far people do not know how to drill wells. The Earth's mantle is now mostly studied using seismic waves. And also by modeling in the laboratory.
According to modern ideas, the internalThe structure of our planet is divided into several layers. The upper one is the crust, then the mantle and the core of the Earth lie. The bark is a hard shell, divided into oceanic and continental. The Earth's mantle is separated from it by the so-called Mohorovicic boundary (named after the Croatian seismologist who established its location), which is characterized by an abrupt increase in the velocities of longitudinal seismic waves.
The mantle is about 67% of the planet's mass. According to modern data, it can be divided into two layers: upper and lower. In the first one, the Golitsyn layer or the middle mantle is also distinguished, which is the transition zone from the upper to the lower. In general, the mantle extends to a depth of 30 to 2900 km.
The core of the planet, according to modernscientists, consists mainly of iron-nickel alloys. It is also divided into two parts. The inner core is solid, its radius is estimated at 1300 km. External - liquid, has a radius of 2200 km. Between these parts a transition zone is distinguished.
The bark and the upper mantle of the Earth are united by the concept"Lithosphere". It is a hard shell with stable and mobile areas. The solid shell of the planet consists of lithospheric plates, which are supposed to move along the asthenosphere - a fairly plastic layer, probably a viscous and highly heated liquid. It is part of the upper mantle. It should be noted that the existence of the asthenosphere as a continuous viscous shell is not confirmed by seismological studies. The study of the structure of the planet makes it possible to distinguish several similar layers located vertically. In the horizontal direction, the asthenosphere, apparently, is constantly interrupted.
Layers lying below the cortex are inaccessible tostudy. Huge depth, a constant increase in temperature, and an increase in density are a serious problem for obtaining information on the composition of the mantle and nucleus. However, it is still possible to imagine the structure of the planet. Geophysical data become the main sources of information in the study of the mantle. The speed of propagation of seismic waves, features of electrical conductivity and gravity allow scientists to make assumptions about the composition and other features of the underlying layers.
In addition, some information is obtainedfrom magmatic rocks and fragments of mantle rocks. The latter include diamonds, which can tell a lot about even the lower mantle. Mantle rocks are also found in the earth's crust. Their study helps to understand the composition of the mantle. However, they do not replace samples obtained directly from deep layers, because as a result of various processes occurring in the crust, their composition is different from the mantle.
Another source of information is thatis a mantle, - meteorites. According to modern ideas, chondrites (the most common group of meteorites on the planet) are close in composition to the earth's mantle.
Of particular interest to scientists are rocks that do not occur in the earth's crust. It is assumed that there are many such compounds in the mantle of grospidites, carbonatites, and so on.
Let us dwell in more detail on the extent of the layersmantle. According to scientists, the upper ones occupy a range of about 30 to 400 km from the earth's surface. Further, there is a transition zone, which extends further 250 km. The next layer is the bottom one. Its boundary is located at a depth of about 2900 km and is in contact with the outer core of the planet.
With the advance into the interior of the planet,temperature. The Earth's mantle is under the influence of extremely high pressure. In the zone of the asthenosphere, the effect of temperature outweighs, so here the substance is in the so-called amorphous or semi-molten state. Deeper under the action of pressure it becomes hard.
The mantle of the Earth does not give rest to scientists already enougha long time. In the laboratories over the rocks, presumably included in the composition of the upper and lower layers, experiments are conducted to understand the composition and characteristics of the mantle. Thus, Japanese scientists have found that the lower layer contains a large amount of silicon. The upper mantle contains water reserves. It comes from the earth's crust, and also penetrates from here to the surface.
Of particular interest is the surfaceMokhorovicic, whose nature is not fully understood. Seismological studies suggest that at a level of 410 km under the surface there is a metamorphic change in the rocks (they become denser), which is manifested in a sharp increase in the speed of wave carrying. It is assumed that the basalt rocks in the region of the Mohorovicic boundary are converted into eclogite. In this case, the mantle density increases by approximately 30%. There is another version, according to which, the reason for changing the speed of seismic waves is the change in the composition of the rocks.
In 2005, Japan built a specialequipped ship Chikyu. His mission is to make a record deep hole at the bottom of the Pacific Ocean. Scientists expect to take samples of rocks of the upper mantle and the boundaries of Mohorovicic to get answers to many questions related to the structure of the planet. The project is scheduled for 2020.
It should be noted that the scientists did not just turnit is to the oceanic subsoil. According to the research, the thickness of the crust on the bottom of the seas is much less than on the continents. The difference is significant: under the water column in the ocean to magma, it is necessary to overcome in some areas only 5 km, while on land this figure increases to 30 km.
Now the ship is already working: samples of deep coal seams were obtained. Realization of the main goal of the project will make it possible to understand how the mantle of the Earth is arranged, what substances and elements make up its transition zone, and also to determine the lower limit of the spread of life on the planet.
Our idea of the structure of the Earth is so far awaynot complete. The reason for this - the complexity of penetration into the interior. However, technical progress does not stand still. The achievements of science suggest that in the not too distant future we will know much more about the characteristics of the mantle.