HOW DO YOU KNOW WHAT IT LOOKS LIKE INSIDE THE EARTH?
One can only look into the earth up to a certain depth. It is 6,000 kilometers to the center of the earth. However, the world’s deepest borehole only goes down to a depth of 12 kilometers. This is just a scratching on the surface or on the earth’s crust.
Earth’s crust, mantle and core
This subdivision relates to the chemical composition. The earth’s crust consists of lighter elements, especially aluminum and silicon. These two elements are the rocks we know: granites, basalts, slates – that is the earth’s crust.
In the earth mantle there are the slightly heavier elements; instead of aluminum, there is more iron and magnesium.
And the Earth’s core is 70 percent iron plus quite a lot of nickel. At its core, therefore, the really heavy material is concentrated. This is the coarse division according to chemistry.
Volcanoes and diamonds provide information about the Earth’s mantle
The information source on the nature of the earth’s interior is:
Volcanoes: There are volcanoes that have their roots at several hundred kilometers deep. That is, the spitting material out of the earth’s mantle. In this respect, they provide information on the chemistry of the earth’s mantle.
Diamonds: Most natural diamonds have formed in the Earth’s mantle and have only later reached the surface through magma streams. When you cut up such diamonds, you always find inclusions of the environment in which they originated – that is, the earth’s mantle.
Magnetic field and meteorites also provide information
One indication of this is the Earth’s magnetic field. For a magnetic field you need a metal, namely a good electrical conductor. The fact that these must be iron is confirmed by another “source of information”: meteorites.
Meteorites are interesting because they formed in our solar system from the same dust cloud as Earth once did. Every now and then someone falls down to the ground. These crashed meteorites can be examined chemically and assume that their total chemical mixture is the same as with the original Earth – because both have been composed of the same dust cloud.
The difference is that on Earth, this mixture has separated. The heavy elements have slumped down into the earth’s interior, the light ones on the edge, on the crust. But since the chemistry of the crust is known – that is the soil under our feet – and at the same time one knows through the meteorites what the overall mixture looked like, one can deduce from it what metals and minerals are available in the earth’s interior.
Seismic measurements
In California, after the earth shakes, people get busy, especially companies like towing services (http://sanjosetowing.org/), the fire department, and practically all government agencies. They want to assure that everyone is safe and try to put things back to the way it was.
In the same manner, the seismology department and other concerned bodies look into the measurement of shockwaves. If the Earth shakes in California, it is possible to measure when and how the shock waves of this quake arrive in Europe or China. And so the scientists gradually got information about how the different layers are made and where in the earth’s interior the boundaries between the different “layers” run.
The boundary between the Earth’s mantle and the Earth’s core, runs almost exactly at half depth, at a depth of 2,900 kilometers. This, in turn, is known above all by seismic measurements: we know that every major earthquake releases shock waves that propagate throughout the globe. However, these shafts have different speeds depending on the material.