This is written as a sequel to ‘Why Earth’s Magnetism?’
The basic thrust of the last article is that the relative rotational movement between Earth’s outermost crust(plates) and the molten crust is the cause of magnetic field.
First, the spinning of Earth along the orbit is likely the result of process that led to the formation of Earth. So the rotational kinetic energy is really the source of Earth’s magnetism. Second, the strength of Earth’s magnetism is too weak if all molten crust is moving in the direction. Third, from common sense, the outer
Consider a ball rotating in the air: First it would gradually slowing down in one direction, then it would spin in the opposite direction; and the process go on indefinitely. And in each iteration, the speed of rotation would be slower than previous iteration.
Now suppose that ball is spinning in the vacuum, then the ball, in principle, would spin forever. When the ball is made of viscous liquid, then there will be a difference of rotational speed at different depth. If this viscous liquid is made of ion, then by Einstein’s theory of relativity, the difference of speed of rotation would be experience as magnetism.
To test this hypothesis, we only need to compare the direction of spinning of Earth and the direction of magnetic pole. Magnetic pole is known to gradually relocating, if my hypothesis is accurate, then this could be explained by the fluid dynamic of the molten crust. Moreover, as the molten crust is slowly solidify due to heat lost by radiation, we would expect a relationship between change of strength of Earth’s magnetic field and the absolute temperature of Earth.