The Earth's magnetic field is constantly changing, although the rate at which it changes varies over time. The Earth's magnetic field is created by the movement of molten iron in its core, which generates electric currents that produce a magnetic field. The field is not constant, and it can change in both intensity and direction.
There are several factors that can affect the Earth's magnetic field, including changes in the Earth's core, solar wind, and the movement of tectonic plates. The Earth's magnetic field has reversed multiple times in the past, with the north and south magnetic poles swapping positions.