archaeomagnetism

Archaeomagnetism is the study of ancient magnetic fields as recorded by archaeological materials. It relies on the fact that fired clay, bricks, pottery, and other heated objects acquire a thermoremanent magnetization as they cool within the Earth’s magnetic field. By measuring the direction and intensity of this magnetization, researchers can reconstruct the geomagnetic field at the time of cooling and, in many cases, date the firing event or the construction phase in which the material was last heated.

Methods in archaeomagnetism involve careful sampling of fired materials such as kilns, hearths, and burned clay features. Laboratory procedures, including stepwise thermal demagnetization or alternating-field demagnetization, are used to isolate the primary magnetization from later alterations. Paleomagnetic analyses yield the ancient field direction and, when possible, paleointensity. The results are compared with regional geomagnetic secular variation curves and, where available, integrated with other dating methods to provide age estimates. The reliability of dating depends on the quality of the magnetization, the preservation of the material, and the availability of a well-characterized regional magnetic field history.

Applications include dating fired archaeological features, such as kilns and hearths, and refining the chronology of archaeological sites. Archaeomagnetism also contributes to reconstructions of past geomagnetic field variations and to methodological cross-checks with radiometric dating and dendrochronology. Limitations arise from post-depositional alteration, later heating, or cooling that resets or overprints the signal, and from the dependence on robust, regionally specific geomagnetic reference data. As a multidisciplinary approach, archaeomagnetism combines field sampling, laboratory magnetism, and geomagnetic modeling to illuminate past human activity and Earth’s magnetic history.