^Cause of earth’s magnetism
1. Gilbert suggested that the earth itself behaves like a giant magnet. The earth’s core is known to contain iron. Yet geologists do not regard this as a source of earth’s magnetism. As the molten iron is not ferromagnetic.
2. Due to Ionization of gases of atmosphere layer of charge particles called ionosphere is formed, which rotates with the rotation of the earth & hence produces magnetism.
Dynamo theory: Rotation of conducting ions of ferromagnetic materials like Fe & Ni in molten state produce current loops & hence magnetism is produced. Although the details of the dynamo effect are not known in detail, at present the dynamo theory seems to be most probable, because our moon which has no molten core, has no magnetism.