Above the T ,cThe Curie Temperature, magnetic minerals (e.g. magnetite) lose their
magnetic properties (atomic dipoles become randomized, no longer lined up).
T c 500°C for magnetite
Only within 20km (too hot past that depth) of the earth’s interior are the rocks
permanently magnetic, called the magnetized layer. This still isn’t enough magnetism to
account for earth’s dipole field. There is a large steel current flowing within the planet.
Iron and nickel are very good at conducting electricity and is rich in the core of the Earth.
The current flow (electric current) is the highest contributing reason for earth’s dipole
field. 4 x 10 Amps of electric current in the core, particularly in the liquid outer core.
Secular Variations of the Earth’s magnetic field
• Rapid variations in direction and magnitude of B in historic time.