Answer:
Although the cause of Earth's magnetism is not exactly known ,several reasonable theories have been proposed. We know that the magnetic fields arise from electric currents. Therefore , all theories explains Earth's magnetism on the basis of electric currents.
1. One theory suggests that the magnetism of Earth may be due to molten charged metallic fluids in the core of the earth . As the Earth rotates about its axis, the charged fluid also rotates . This give rise to electric currents in the fluid.These electric currents are responsible for Earth's magnetism.
2. Another theory suggests that since Earth has charged particles ( protons and electrons), the rotation of Earth about its axis generates electric currents . These current magnetise the Earth.
3. There is yet another view regarding Earth's magnetism. High- energy rays coming from the sun collide with the atoms of gases in the upper layers of the atmosphere and ionise them . The rotation of Earth causes movement of the ions and hence strong electric currents are set up . The magnetism of Earth is due to this currents.
iron in the core,<<< That was one correct way to see theanswer. We also have to take into account is the Rotation of the Earth. The central core is surrounded by super heated Magma which is lubricate by the Earth it self . As the center of the Earth rotates. we also have earth it self turn alot slower. This cause the Friction that bulids up the energy that create the Magnitic Field.
The solid Iron core in the middle of Earth has a polarity of it's own. The Earth consist of three layer - Crust, Mantle, Core.
The crust is what we live on, the mantle is solid (According to science) or liquid (This is geography's definition), and the outer core is liquid, the inners core is solid, and consists mainly of Iron and Nickel.
A spinning Iron core.