Paleomagnetism reconstructs past magnetic fields from remanent magnetization in rocks and other materials. Cooling volcanic minerals can acquire thermoremanent magnetization; later heating, alteration or mineral growth can change the record.
An oriented field sample preserves the relation between the measured magnetic direction and its geological setting. Shielded laboratory magnetometers and stepwise heating or alternating-field treatment help separate components acquired at different times. Combined with independent ages and structural corrections, the results test continental reconstruction and past field reversals.[ref]
Rocks and Paleomagnetics Laboratory by United States Geological Survey. Facilities and equipment: sample orientation, magnetic shielding and demagnetization
Paleomagnetism is the study of the Earth’s magnetic field as preserved in rocks, sediments, and archaeological materials. It involves the analysis of the magnetic properties of these materials to understand the history of the Earth's magnetic field, including its direction and intensity over geological time. When volcanic rocks form, or sediments are deposited, they can acquire a remnant magnetization that reflects the Earth's magnetic field at that moment in time.
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