The earth’s crust consists of a stone layer situated below the continents and the oceans. Under this lies the mantle: a 2900 kilometre deep impenetrable shell surrounding the outer core of the earth. Generally, the closer you get to the core of the earth, the higher the temperature. Nevertheless, not all the stone will melt due to the enormous pressures down there. The pressure is so high that at a depth of 1000 metres, stone is harder than steel. Even on the boundary of the mantle and the earth’s core, stone is four times stronger than steel.
The ground we walk on is the earth’s crust, measuring 30 to 50 kilometres thick. This crust primarily consists of stones which are similar to granite or granodiorite. These stones contain the elements silicon and aluminium. Beneath this layer, basalt and gabbroid can generally be found. A characteristic of basalt is the vertical columns, which originate from the solidifying and cooling-off of lava. These columns can be found at the Giant’s Causeway in Ireland and the Devil's Tower in Wyoming. Beneath mountains, the earth’s crust can be up to 60 kilometres thick. Underneath the oceans however, the crust is thinner than under land. On the bottom of the ocean, there is a layer of sediment, of approximately one kilometre thick. Below this is a basalt layer of five kilometres.
Four elements alone make up almost 90 percent of the earth’s crust. These are oxygen, silicon, aluminium and iron. The other elements make up the remaining 10 percent and are only present in small amounts. Knowledge about the earth’s crust is rather limited because we only have accurate calculations for the first 16 kilometres.
To find out how the earth’s crust is constructed, explosive charges can be triggered at set depths. As a result of these explosions, the stones in the earth’s crust tremble. Special seismographic equipment can detect these vibrations. The vibrations supply us with information about the crust's structure.
Drilling to petroleum also supplies us with information about the structure of the earth’s crust. Today, one can reach a depth of about 1.5 kilometres. In 1970, the Russians set a new record. They started to bore out a tunnel which had to reach a depth of 15 kilometres. Twenty-five years later, they were stuck at a depth of 12.6 kilometres. A human being could never survive down there because the temperature was 230 degrees Celsius! For every 100 metres you go down, the temperature increases by 3 degrees.