What is the cause of earth's magnetism?

What is probable cause of earth's magnetism?

The horizontal component of earths's magnetic field at a place is 0.3 xx 10^-4T . If the angle of dip is 60^@ , what is the total earth's magnetic field?

The motion of copper plate is damped, when it is allowed to oscillate between the two poles of a magnet. What is the cause of this damping?

Give the possible causes of earth magnetic field.