The inner structure of the Earth

From space we see the Earth surrounded by the air shell – the atmosphere, the water shell – the hydrosphere, and the shell of living organisms – the biosphere. Below them lies the Earth’s crust made of solid rock; its average thickness is 35–40 km under the continents, about 5 km under the oceans and more than 70 km under high mountains. Under the crust lies the mantle, about 2900 km thick (the textbook gives 2860 km). At the centre is the core: the outer core is liquid and the inner core is solid, and the core’s radius is about 3480 km (the textbook gives a diameter of 6940 km). Temperature rises with depth – by about 30 °C per kilometre in the crust and above 5000 °C in the core. The Earth’s interior cannot be seen directly; we learn about it from volcanic materials and earthquake waves. The deepest borehole (Kola, Russia) reached only a little more than 12 km.