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The earth consists of several layers. The three main layers are the core, the mantle and the crust. The core is the inner part of the earth, the crust is the outer part and between them is the mantle. The earth is surrounded by the atmosphere. Till this moment it hasn't been possible to take a look inside the earth because the current technology doesn't allow it. Therefore all kinds of research had to be done to find out, out of which material the earth consists, what different layers there are and which influence those have (had) on the earth's surface. This research is called seismology |
THE
CORE |
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What
Influence does the Core have?
Because the core is so hot, it radiates a natural heat to the upper layers.
Because of this a current of heat comes into being. Those are also known
as the convection currents. The convection currents cause the movement
of the tectonic plates. This movement is called plate tectonics.
The outer core and the inner core together cause the earth's magnetism.
Because the earth rotates, the outer core spins, the inner core doesn't
spin because it's solid. This gives a kind of dynamo effect and causes
the earth's magnetism. Magnetism has been used by sailors to find their
way on earth for thousands and thousands of years. Magnetism also influences
electro-particles outside the atmosphere of the earth, up to more than
37,000 miles (60,000 km) into space
THE
MANTLE
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.
What Influence does the Mantle Have?
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.
THE CRUST
The crust covers the mantle and is the earth's hard outer shell, the surface on which we are living. Compared to the other layers the crust is much thinner. It floats upon the softer, denser mantle. The crust is made up of solid material but this material is not the same everywhere. There is an Oceanic crust and a Continental crust. The first one is about 4-7 miles (6-11 km) thick and mainly consists of heavy rocks, like basalt. The Continental crust is thicker than the Oceanic crust, about 19 miles(30 km) thick. It is mainly made up of light material like granite.
What does the crust consist of?
The crust consists of two parts: the oceanic and the continental crust.
Oceanic crust:
As the name already suggests, this crust is below the oceans. There, the crust is 4-7 miles (6-11 km) thick. The rocks of the oceanic crust are very young compared with the rocks of the continental crust. The rocks of the oceanic crust are not older than 200 million years. The material of which the oceanic crust consists is for the greater part tholeiitic basalt (this is basalt without olivine). Basalt has a dark, fine and gritty volcanic structure. It is formed out of very liquid lava, which cools off quickly. The grains are so small that they are only visible under a microscope. The average density of the oceanic crust is 3g/cm³.
Continental crust:
When you look at the globe, you see that the surface of the earth consists of a lot of water (71%). The other 29% consists of land. You can divide this land into six big pieces, which are called continents. The different continents - arranged in decreasing order of size - are: Eurasia (Europe and Asia together), Africa, North-America, South-America, Antarctica and Australia. In the past the division of the continents was different.
The earth's crust is the thickest below the continents, with an average of about 20 to 25 miles (30 to 40 km) and with a maximum of 45 miles (70 km). The continental crust is older than the oceanic crust, some rocks are 3.8 billion years old. The continental crust mainly consists of igneous rocks and is divided into two layers.
The upper part mainly consists of granite rocks, while the lower part consists of basalt and diorite. Granite is lightly-colored, coarse-grain, magma. Diorite has the same composition, but it's scarcer than granite and is probably formed by impurities in the granite-magma. The average density of the continental crust is 2.7g/cm³.
Which influence does the crust have?
The crust itself has no influence on the earth, but the constant moving of the crust does. This moving is caused by the influence of the convection current, or to be more precise, this convection current actually causes the earth plates to move and sometimes touch each other. These movements cause earthquakes and at weak parts of the earth's crust volcanoes can erupt. Because of all these ongoing movements in the last millions of years, mountains and valleys have been formed, and that’s why the surface of the earth looks as it is now. The form of the surface of the earth has its daily influence on the way people live and work. An example: the building of houses. When you build a house in the mountains, you build it in an other way than on flat land. In the mountains the bottom is more solid than on flat land.