Earth's magnetic field is produced by permanent magnetism in its iron-rich core.

Earth’s magnetic field looks roughly like the field around a giant bar magnet. That made a permanently magnetized iron-rich core an intuitive early explanation.

The problem is temperature. Ordinary iron can behave as a permanent magnet only below a temperature called the Curie temperature. Above it, thermal motion destroys the organized magnetic alignment needed for ferromagnetism.

Earth’s core is far hotter than that.

The field also behaves unlike a fixed buried magnet. Its strength and direction change measurably over time, and the planet’s magnetic polarity has reversed many times in the geological past.

Seismology supplied another important clue by showing that Earth’s outer core is liquid. It is made largely of electrically conducting metal.

When this liquid metal moves, it can generate electric currents. Those currents produce magnetic fields, and the combined motion of the fluid, convection, and Earth’s rotation can keep the process going. This self-sustaining mechanism is called the geodynamo.

Earth therefore still resembles a dipole, or simple two-pole magnet, when viewed from far away. But the source of that field is moving conductive fluid, not a permanent bar magnet hidden at the center.