archaeomagnetism-dating

Archaeomagnetic dating

Archaeomagnetism dating (adjective 'archaeomagnetic') is the science of how to interpret signatures of the Earth's magnetic field at past times that are recorded in archaeological materials. These paleomagnetic signatures can be recorded when materials were heated by ancient fires. The signatures of past directions of the magnetic field of the Earth can be used to constrain ages of the materials. In conjunction with techniques such as carbon dating, the technique can be used to infer possible ages of the heating.

The basis of the dating is Thermal Remnant Magnetism (TRM), discussed in the entry on paleomagnetism. At the time of firing, the direction and intensity of the magnetic field of the Earth may be recorded by iron-bearing minerals such as magnetite contained in baked ceramic material. The ceramic material must be locked into position in the earth, such as in a hearth pit or fire-hardened surface. As time passes, the magnetic field direction of the local environment varies from the direction locked into the ceramic material. The change observed between the present and the recorded magnetic fields may be useful in constraining the elapsed time.

Instances of use

The Earth's magnetic field reverses direction at irregular intervals, and local directions and intensities change gradually (secular variation). These changes can be used to constrain ages of baked materials.

References

Herries, A.I.R., Kovacheva, M., Kostadinova, M., Shaw, J., 2007. Archaeo-directional and -intensity data from burnt structures at the Thracian site of Halka Bunar (Bulgaria): The effect of magnetic mineralogy, temperature and atmosphere of heating in antiquity, Physics of the Earth and Planetary Interiors. 162, 199-216.

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