Causes of the Earth’s Magnetic Field

Several theories have been suggested form time to time to account for earth’s magnetic field. But no single theory is able to explain all the facts about the earth’s magnetic behavior.

(i)    Gilbert in 1600 stated that the earth’s is a ‘great magnet’. The experimental facts are not in favor of this theory because the earth is not completely made up of magnetic materials.

(ii)    Grover attributed the magnetism of the earth to be due to the electric current circulation around the earth. These currents are generated due to sun. Hot air, rising from the region near equator, goes towards northern and southern hemispheres and becomes electrified. These currents magnetize the ferromagnetic materials near the outer surface of the earth.

(iii)    There is another view regarding earth’s magnetism. The temperature inside earth’s crust is very high. Therefore there are many conducting materials including iron and nickel in the molten state within the central core of the earth. Conventional currents are set up in this semi-fluid core due to earth’s rotation about its axis. Because of this, the process of self-excited dynamo starts within earth. Therefore, electric current, and hence magnetism, is generated with earth. Most of the earth’s magnetism is supposed to be generated due to this reason.

(iv)    The fourth view about earth’s magnetism is that gases are present in ionized state in the atmosphere. High-energy rays coming from sun collide with the atoms of gases in the upper layers of the atmosphere and ionize them. The radio activity of the atmosphere and the cosmic rays also ionize the gases. A conducting layer of charge particles called ionosphere is formed. With the rotation of earth ionosphere also rotates. Hence, strong electric currents flow due to earth’s rotations Earth’s magnetic field is generated due to these currents.


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