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The boundary between the crust and the mantle is the Mohorovicic discontinuity, named for its discoverer, and is usually called the Moho. The Moho is a boundary at which there is a sudden change in the speed of seismic waves. At one time some thought that the Moho was the structure at which the earth's rigid crust moved relative to the mantle. Current research places this zone of movement within the mantle, from 70 km (43 mi) below the ocean crust to 150 km (93 mi) below the continental crust. The mantle just below the crust is composed of rigid, solidified, basaltic rock fused to the crust but at the same time separated from it by the Moho. This rigid layer of crust and the upper mantle forms the lithosphere.

The mantle differs substantially from the crust in its mechanical characteristics and its chemical composition. It is chiefly the difference of chemistry on which the distinction between crust and mantle is based. Mantle rock consists of olivines, different pyroxenes and other mafic minerals. Typified by peridotite, dunite, and eclogite, mantle rocks also possesses a higher portion of ironThis article is about metallic iron. For the ironing device, see ironing manganese iron cobalt Fe Ru Full table General Name, Symbol, Number iron, Fe, 26 Chemical series transition metal Group, Period, Block 8 (VIIIB), 4 , d Density, Hardness 7874 kg/m3, and magnesiumMagnesium is the chemical element in the periodic table that has the symbol Mg and atomic number 12. Magnesium is the eighth most abundant element and constitutes about 2% of the Earth's crust, and it is the third most plentiful element dissolved in seawa and a smaller portion of siliconSilicon is the chemical element in the periodic table that has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon. It is the second most abundant element in the Earth's crust, making up 25 and aluminiumAluminium (or aluminum in North American English) is the chemical element in the periodic table with the symbol Al and atomic number 13. A silvery and ductile member of the poor metal group of elements, aluminium is found primarily as the ore bauxite and than the crust. In the mantle, temperatures range between 100°C at the upper boundary to over 3,500°C at the boundary with the coreScience In biology the core of a fruit contains its seeds. In planetary science the core of a planet contains its innermost layer(s). Due to planetary differentiation, such layers tend to be more dense than outer layers. In archaeology a core is a distinc. Although these temperatures far exceed the melting pointThe melting point of a solid is the temperature at which it changes state from solid to liquid. When considered as the temperature of the reverse change, it is referred to as the freezing point . For example, the melting point of the element mercury is 23s of the mantle rocks, particularly in deeper ranges, they are almost exclusively solid. The enormous lithostatic pressure exerted on the mantle prevents them from melting.

The subregion of the mantle extending about 250 km (155 mi) below the lithosphere is called the asthenosphereThe asthenosphere (from the Greek asthenia "weakness") is the region of the Earth between 100-200 km below the surface, but may extend as deep as 400 km. It is the weak or "soft" zone in the upper mantle just below the lithosphere that is involved in plat. This region of the mantle passes seismic waves more slowly, leading this region to also be called the low-velocity zone. The conditions of temperature and pressure here make this material semi-molten, or plastic.

Due to the temperature difference between the Earth's crust and outer core there is a convective material circulation in the asthenosphere. Hot material ascends as a plutonic diapir from the border with the core, while cooler (and heavier) material sinks downward. During the ascent the material of the mantle cools down adiabatically. The temperature of the material falls with the pressure relief connected with the ascent, and its heat distributes itself over a larger volume. Near the lithosphere the pressure relief can lead to partial melting of the diapir, leading to volcanism and plutonism.

The convection of the Earth's mantle is a chaotic process (in the sense of fluid dynamics), which is thought to drive continental drift. The movements of the continents and the Earth's mantle are thereby partially decoupled, since due to the rigidity of the crust, a tectonic plate can only move as a whole. Continental drift is therefore only a diffuse image of the movements at the upper limit of the Earth's mantle. The convection of the mantle is not yet clarified in detail. There are different theories, according to which the Earth's mantle is divided into different floors of separate convection.

Although there is a tendency to larger viscosity at greater depth, this relation is far from linear, and shows layers with dramatically decreased viscosity, in particular in the upper mantle and at the boundary with the core [1].

Due to the low viscosity in the upper mantle one could reason that there should be no earthquakes below approximately 300 km depth. However, deep earthquakes with foci between 400 km and 670 km under the earth's surface have been registered.