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Origin of Earth's Magnetic Field
Earth has a solid inner core (Fe, Co) and liquid outercore. The second figure shows the reason for the solid nature of inner core (increase in melting point of inner core Fe with pressure).
The liquid outercore of earth generate current loop which acts like a geodynamo in generating earths magnetic field. The geographical north pole is the magnetic south and vice versa. The pole has reversed its direction 171 times during the past 71 million years.
* Melting starts at 225+/- 3 GPa (5100 +/- 500 K) and is complete at 260 +/- 3 GPa (6100 +/- 500 K).
* Inner core radius – 1,220 km (P=329 GPa)
* Outer core radius – 3,490 km (P=136 GPa)
* Viscosity of liquid outer core similar to water
* Fluid velocity – 10 km/year
* Transport of heat through mantle is crucial for powering the geodynamo
* Molten earth during accretion caused heavy elements of Fe sink to the core
* Gravitational interaction between core and mantle prevent relative rotation
* Elastic anisotropy – seismic waves travel faster along polar path than equatorial path – preferred orientation of Fe crystals