The layered structure of the Earth

In short: The Earth is built like an onion of several layers: crust, mantle, outer core and inner core. The deeper you go, the hotter and denser it gets.

In more detail: The Earth’s radius is about 6,370 kilometres, yet the deepest borehole reaches only about 12 kilometres down. What we know about the interior comes mainly from earthquake waves, which travel at different speeds depending on the material, are bent, or are not passed on at all.

In detail

• Crust: The thin outermost layer is usually only 5 to 10 kilometres thick under the oceans and about 30 to 70 kilometres under the continents, thickest under high mountain ranges.
• Mantle: It reaches down to about 2,900 kilometres and makes up most of the Earth’s volume. Its rock is solid but can flow very slowly over long periods of time.
• Lithosphere and asthenosphere: The crust and uppermost mantle together form the rigid lithosphere, which is broken into plates. Beneath it lies a softer zone on which the plates slide.
• Outer core: From about 2,900 to 5,100 kilometres deep, the core consists of liquid iron and nickel. Its currents generate the Earth’s magnetic field.
• Inner core: At the centre lies a solid ball of iron and nickel with a radius of just over 1,200 kilometres. Despite temperatures of several thousand degrees it stays solid because of the enormous pressure.
• Heat inside: The core is about as hot as the surface of the Sun. The heat comes partly from the time the Earth formed and partly from the decay of radioactive substances.
• Evidence from earthquake waves: Certain waves, called S-waves, cannot travel through liquids. The fact that they do not cross the outer core shows that it is liquid.
• Felt at the surface: The internal heat drives volcanoes, earthquakes and the movement of the continents, and can be used in hot springs and geothermal energy.
• Connections: Plate tectonics, the magnetic field and volcanism all originate in the Earth’s interior (plattentektonik, erdmagnetfeld, erdbeben-und-vulkane).