The layer above the core is the mantle. It begins about 6 miles(10 km) below the oceanic crust and about 19 miles (30 km) below the continental crust (see The Crust). The function of the mantle is to separate the inner mantle and the outer mantle. It is about 1,800 miles(2,900 km) thick and makes up nearly 80 percent of the Earth's total volume.
Science deals with the structure of the mantle in two different ways. One way is based on its chemical construction (the material), the other on the way layers stream or move.
What does the mantle consist of?
Based on the chemical construction:
Inner Mantle: the inner mantle can be found between 190 miles (300 km) an 1,800 miles (2,890 km) below the earth’s surface. The average temperature is 5400 ºF (3000ºC), nevertheless the rock is solid because of the high pressures. The inner mantle for the biggest part probably consists of sulphides and oxides of silicon and magnesium. The density is between 4.3g/cm³ and 5.4g/cm³.
Outer Mantle: The outer mantle is a lot thinner than the inner mantle. It can be found between 7 miles (10 km) and 190 miles (300 km) below the surface of the earth. You can divide the outer mantle into two different layers. The bottom layer is tough liquid rock and probably consists of silicates of iron and magnesium. The temperature in this part is between 2520 ºF (1400ºC) and 5400 º F (3000ºC) and the density is between 3.4g/cm³ and 4.3g/cm³. The upper layer of the outer mantle consists of the same material but is stiffer because of its lower temperature.
From this perspective, you look at the outer mantle and the
crust together. Here we make a difference in asthenosphere and lithosphere.
|What Influence does the Mantle
Because the earth is very hot inside, a current of heat flows from the core to the crust. This is called convection current and it also takes place in the mantle. This current cools down as it comes closer to the surface of the earth. As a result, the rising of the current decreases and goes into horizontal direction along the bottom of the crust. When the current cools down more, the convection current descends again and goes to the inner earth. There the temperature increases and the current rises again. This goes on and on.
When the current comes at a weaker part of the crust, for example at a volcano, magma comes above the earth's surface. The convection current along the bottom of the crust causes the moving of the tectonic plates. This is called plate tectonics. The movement of these plates goes very slowly. The bumping of two tectonic plates causes an earthquake.
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