Geodynamo (Dynamo of the Earth)
The magnetic field of the earth is originated in an huge electric magnet generated in the outer core, where melten metal (mainly iron and nickel) is convecting.
The magnetic field is generated and maintained by a cycle with two physical processes following,
1. electric conductance flows in magnetic field → current occurs (electric induction)
2. electric current → magnetic field is generated (magnetic indcution, Ampair's low)
This is called Geodynamo process (cycle).