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Why was the theory of a permanently magnetized Earth rejected?

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geomagnetic field The magnetic field of a bar magnet has a simple configuration known as a dipole field. Close to Earth's surface this field is a reasonable approximation of the actual field.

The theory that Earth contains a permanent magnet, such as a giant lodestone or iron bar, was rejected because it is physically impossible for such a magnet to exist within the planet's interior.

Geophysical measurements and projections of internal pressure and temperature demonstrate that the Curie point—the temperature at which magnetic materials lose their permanent magnetic properties—is exceeded at depths of only 10 to 40 km (6 to 25 miles) below the surface. Because the interior of the Earth is far hotter than this threshold, any permanent magnetic material would lose its magnetism, rendering the bar-magnet hypothesis untenable.1

Instead, the scientific consensus supports dynamo theory, which posits that the geomagnetic field is generated by a self-sustaining process in the Earth's outer core. In this mechanism, the motion of liquid iron conducts electricity, creating a magnetic field that is maintained by convective currents. This theory also accounts for observed magnetic reversals, which a permanent magnet could not explain.213