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geomagnetism [Q&A]

Vinay

Madhusoodan of Poornaprajna College asks, what causes the Earth to have a magnetic field?

Typically, magnetic fields in astronomical objects are generated via a natural dynamo. Starting from a seed field which is embedded in the medium, the object first amplifies this field by wrapping it around via rotation, and then rearranges it via convection. On the Sun, this type of dynamo is thought to be acting just below the surface. On the Earth, the dynamo is thought to be in the core. The field is thought to be generated via induced eddy currents in the molten outer core, and maintained via rotation and convection driven by thermal and chemical buoyancy. The process is efficient enough to overcome dissipation and maintain a relatively steady half-Gauss field at the surface. The theory to explain how exactly this field is generated, what governs its strength and polarity, what causes it to reverse polarity and at what timescale, etc., is not fully developed.