The Earth's mantle is the part of the geosphere located between the crust and the core. It contains a large proportion of the entire substance of the planet. The study of the mantle is important not only in terms 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 the movement of lithospheric plates. However, obtaining information about the composition and features of the mantle is not easy. People do not yet know how to drill wells so deep. The Earth's mantle is now mainly studied using seismic waves. And also by modeling in the laboratory.
The structure of the Earth: mantle, core and crust
According to modern concepts, the internal 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 crust is a hard shell divided into oceanic and continental. The Earth's mantle is separated from it by the so-called boundaryMohorovicic (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 makes up about 67% of the planet's mass. According to modern data, it can be divided into two layers: upper and lower. In the first, the Golitsyn layer or the middle mantle is also distinguished, which is a transition zone from the upper to the lower. In general, the mantle extends from 30 to 2900 km.
The core of the planet, according to modern scientists, 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. A transition zone is distinguished between these parts.
Lithosphere
The crust and the upper mantle of the Earth are united by the concept of "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 through the asthenosphere - a rather 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 allows us to identify several similar layers located vertically. In the horizontal direction, the asthenosphere, apparently, is constantly interrupted.
Methods of studying the mantle
The layers below the crust are inaccessible tostudy. The enormous depth, the constant increase in temperature and the increase in density are a serious problem for obtaining information about the composition of the mantle and core. However, it is still possible to imagine the structure of the planet. When studying the mantle, geophysical data become the main sources of information. The speed of seismic waves, electrical conductivity and gravity allow scientists to make assumptions about the composition and other features of the underlying layers.
In addition, some information can be obtained from igneous rocks and fragments of mantle rocks. The latter include diamonds, which can tell a lot even about 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 will not replace samples taken directly from the deep layers, since as a result of various processes occurring in the crust, their composition is different from the mantle.
Earth's Mantle: Composition
Meteorites are another source of information about what the mantle is. According to modern concepts, chondrites (the most common group of meteorites on the planet) are close in composition to the earth's mantle.
It is supposed to contain elements that were in a solid state or were in a solid state during the formation of the planet. These include silicon, iron, magnesium, oxygen and some others. In the mantle, they combine with silicon dioxide to form silicates. ATmagnesium silicates are located in the upper layer, the amount of iron silicate increases with depth. In the lower mantle, these compounds decompose into oxides (SiO2, MgO, FeO).
Of particular interest to scientists are rocks that are not found in the earth's crust. It is assumed that there are many such compounds (grospidites, carbonatites, etc.) in the mantle.
Layers
Let's take a closer look at the length of the mantle layers. According to scientists, the upper ones occupy a range of approximately 30 to 400 km from the earth's surface. Next is the transition zone, which goes deeper into the depths for another 250 km. The next layer is the bottom. Its border is located at a depth of about 2900 km and is in contact with the outer core of the planet.
Pressure and temperature
As you move deeper into the planet, the temperature rises. The Earth's mantle is under extremely high pressure. In the asthenosphere zone, the effect of temperature outweighs, so here the substance is in the so-called amorphous or semi-molten state. Deeper under pressure, it becomes solid.
Studies of the mantle and the Mohorovicic boundary
The mantle of the Earth haunts scientists for quite a long time. In laboratories, experiments are being carried out on rocks that are presumably part of the upper and lower layers, allowing us to understand the composition and features of the mantle. Thus, Japanese scientists found that the lower layer contains a large amount of silicon. The upper mantle contains water reserves. She comes fromthe earth's crust, and also penetrates from here to the surface.
Mohorovicic's surface is of particular interest, the nature of which is not fully understood. Seismological studies suggest that at a level of 410 km below the surface, a metamorphic change of rocks occurs (they become denser), which manifests itself in a sharp increase in the speed of waves. It is assumed that the bas alt rocks in the area of the Mohorović boundary turn into eclogite. In this case, the density of the mantle increases by about 30%. There is another version, according to which, the reason for the change in the speed of seismic waves lies in the change in the composition of the rocks.
Cikyu Hakken
In 2005, a specially equipped ship Chikyu was built in Japan. His mission is to make a record deep well at the bottom of the Pacific Ocean. Scientists propose to take samples of the rocks of the upper mantle and the Mohorovichic boundary in order to get answers to many questions related to the structure of the planet. The project is scheduled for 2020.
It should be noted that scientists have not just turned their attention to the oceanic depths. According to studies, the thickness of the crust at the bottom of the seas is much less than on the continents. The difference is significant: under the water column in the ocean, it is only 5 km to overcome magma in some areas, while on land this figure increases to 30 km.
Now the ship is already working: samples of deep coal seams have been received. The implementation of the main goal of the project will make it possible to understand how the Earth’s mantle is arranged, whatsubstances and elements constitute its transition zone, as well as to find out the lower limit of the spread of life on the planet.
Our understanding of the structure of the Earth is far from complete. The reason for this is the difficulty of penetrating into the bowels. However, technological progress does not stand still. Advances in science suggest that we will know much more about the characteristics of the mantle in the near future.
