Scientists have hypothesized and made predictions about the cause of the Earth's magnetic fields, and the prevailing theory is that the Earth's magnetism originates from the planet's center, or core. Because scientists don't have the ability to travel to the center of the Earth by any means, whether physically, virtually or remotely, there is no way to definitively test this hypothesis. The magnetic field results from circulating currents that are described by the term "dynamo effect," and the direction of these circulating currents changes periodically, a phenomenon that is observable in the different directions of permanent magnetism found in rocks of different ages.
The Earth's magnetic field resembles that of a bar magnet, with north and south poles and magnetic field lines that radiate from one pole to another. Although it is believed that the Earth's magnetism originates from circulating electrical currents in the planet's molten core, this part of the planet is incredibly hot; in fact, too hot to itself be magnetic. The Earth's rotation on its axis is also related to the planet's magnetic field, a theory that scientists link to the fact that Venus lacks a measurable magnetic field but has a molten iron core similar to that of Earth and has a different rotational period.