Correct answer: Magnetic field is created when molten material is heated from earth's core.
Due to the movement of molten iron and nickel inside the core of the earth magnetic field is generated. Due the the generation of high temperature all the molten material are in the liquid form. A Coriolis force is generated due to flow of molten liquid, which result in the formation of magnetic field.
The magnetic field of the earth is used to protect the earth from the harmful solar radiation .