Caves and mines go only up to 1-2 km inside the Earth. Even the deepest wells of the world, such as the one 12 km deep in the Russian Kola Peninsula or the 9-km-deep one in the Upper Palatinate, hardly scratch the Earth’s crust. One can ‘look’ deep inside the Earth in the aftermath of earthquakes or by creating nuclear explosions. The explosions generate sound or seismic waves. They also throw off rock particles. By measuring their intensity and timings, scientists discover the composition of the Earth’s interiors.
