Paleomagnetism
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Paleomagnetism refers to the orientation of the Earth's magnetic field as it is preserved in various magnetic iron bearing minerals throughout time. The study of paleomagnetism has demonstrated that the Earth's magnetic field has changed both in orientation and intensity over time.
Paleomagnetism can be divided into two fields:
- Polar wandering: the magnetic north pole is constantly shifting relative to the axis of rotation. This is responsible for the shifting magnetic declination required for compass work and orienteering.
- Magnetic polarity reversals: periodically, the Earth's magnetic field reverses polarity. The reversals have occurred at irregular intervals throughout the Earth's history.
The study of paleomagnetism is possible because iron-bearing minerals such as magnetite in basalt and other igneous rocks become aligned with the Earth's magnetic field at the time of the rock's solidification.
Paleomagnetic evidence, both reversals and polar wandering data, was instrumental in verifying the theories of continental drift and plate tectonics in the 1960s and 70s.