Paleomagnetism

Paleomagnetism (occasionally palaeomagnetism) is the study of prehistoric Earth's magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called paleomagnetists.

Certain magnetic minerals in rocks can record the direction and intensity of Earth's magnetic field at the time they formed. This record provides information on the past behavior of the geomagnetic field and the past location of tectonic plates. The record of geomagnetic reversals preserved in volcanic and sedimentary rock sequences (magnetostratigraphy) provides a time-scale that is used as a geochronologic tool.

Evidence from paleomagnetism led to the revival of the continental drift hypothesis and its transformation into the modern theory of plate tectonics. Apparent polar wander paths provided the first clear geophysical evidence for continental drift, while marine magnetic anomalies did the same for seafloor spreading. Paleomagnetic data continues to extend the history of plate tectonics back in time, constraining the ancient position and movement of continents and continental fragments (terranes).

The field of paleomagnetism also encompasses equivalent measurements of samples from other Solar System bodies, such as Moon rocks and meteorites, where it is used to investigate the ancient magnetic fields of those bodies and dynamo theory. Paleomagnetism relies on developments in rock magnetism and overlaps with biomagnetism, magnetic fabrics (used as strain indicators in rocks and soils), and environmental magnetism.