It was always interesting to people to learn what is at them underfoot. As in ancient times the significant facts concerning the structure of Earth, scientists had no, they made various assumptions, placing in the center of the planet a turtle, an elephant or one more planet, smaller on diameter, with own inhabitants. Today any school student will tell that in the center of Earth there is a kernel.
Earth kernel
The top cloak of a kernel of Earth is located in the center of the planet at a depth from 2900 km. The mass of the center about 31% of mass of all Earth are, volume occupies about 16% of volume of the planet. From this ratio it is possible to understand that the kernel consists of very dense and heavy materials. Presumably, this material is alloy of nickel and iron.
Researches show that density of a kernel is non-uniform: its external layers are in liquid state, and an internal part – in firm. Such heterogeneity is caused by the fact that the kernel is exposed to huge pressure. Different temperature of a kernel of the earth is specified in different sources: 4000 – 7000 degrees Celsius.
Methods of researches
All researches of the center of Earth are conducted by indirect methods as samples of the substance which is in the planet cannot be taken. Modern technologies allow to get deep into planets only on 12 km. To get an idea of what happens in the center of Earth scientists study seismic waves. In different corners of the planet the seismic stations registering fluctuations of earth crust during earthquakes are constructed. Also scientists investigate the pieces of asteroids arriving to us from space. Analyses show that asteroids consist of iron-nickel alloys therefore geophysics came to a conclusion about that, as the kernel of Earth can consist of such alloy. However other scientists claim that in the center of the planet there are also other, less dense chemical elements. Metal "basis" of Earth, together with its rotation, is the reason of emergence of magnetic field.
Scientific and pseudo-scientific theories
At different times various scientists put forward the theories of the structure of Earth. The classical theory of the American researchers of Read and Raid suited geologists and mineralogists, but it was not pleasant to those who ever saw how there is a drilling on depth exceeding 7 km. Schools of children teach that in the planet the kernel from iron-nickel alloy is located, but the universities of professor add to it that I a kernel constantly there are nuclear reactions. The Soviet academician Vladimir Obruchev developed the theory of the hollow planet. Obruchev assumed that Earth represents a hollow sphere in which – the zero gravity, and is a kernel from very dense material in the center of this emptiness. However by the time of development of this theory Read Raid concept so strongly took roots in school textbooks that Obruchev could present the theory to readers only in the form of the work of art – the famous novel of "Plutonium".