Dunlop, David J. Department of Physics, University of Toronto, Ontario, Canada.
Last reviewed:January 2020
- Origin of rock magnetism
- Magnetization processes
- Laws of partial TRM
- Induced magnetization and magnetic anomalies
- Magnetic minerals
- Seafloor spreading and linear magnetic anomalies
- Paleomagnetic evidence for continental drift and plate tectonics
- Magnetic field reversals and magnetostratigraphy
- Magnetic records from lake sediments, soils, and loess
- Paleointensity variation
- Paleomagnetism of other planets
- Related Primary Literature
- Additional Reading
The permanent and induced magnetism of rocks and minerals on scales ranging from the atomic to the global, including applications to magnetic field anomalies and paleomagnetism. Natural compasses, concentrations of magnetite (Fe3O4) called lodestones, are one of humankind's oldest devices. W. Gilbert in 1600 discovered that the Earth itself is a giant magnet, and speculated that its magnetism might be due to subterranean lodestone deposits. Observations by B. Brunhes in 1906 that some rocks are magnetized reversely to the present Earth's magnetic field, and by M. Matuyama in 1929 that reversely and normally magnetized rocks correspond to different geological time periods, made it clear that geomagnetism is dynamic, with frequent reversals of north and south poles. Nevertheless, permanent magnetism of rocks remains important because it alone provides a memory of the intensity, direction, and polarity of the Earth's magnetic field in the geological past. From this magnetic record comes much of the evidence for continental drift, seafloor spreading, and plate tectonics. See also: Continental drift; Geomagnetism; Magnet; Magnetism; Paleomagnetism; Plate tectonics
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