Archaeomagnetic dating sites
Within these weaker areas the local directions and intensities change gradually (secular variation).A compass does not point to the true North Pole but to direction that is a function of the North Magnetic Pole and the local secular variation to yield a magnetic declination.This is one of the dating methodologies used for sites within the last 10,000 years. Thellier in the 1930s and the increased sensitivity of SQUID magnetometers has greatly promoted its use.The Earth's magnetic field has two main components.Archaeomagnetic dating is the study and interpretation of the signatures of the Earth's magnetic field at past times recorded in archaeological materials.These paleomagnetic signatures are fixed when ferromagnetic materials such as magnetite cool below the Curie point, freezing the magnetic moment of the material in the direction of the local magnetic field at that time.Additional data points from archaeomagnetic samples with corresponding dating techniques such as tree ring dating or carbon-14 dates, help refine the regional curves.A number of samples are removed from the feature by encasement in non-magnetic plaster within non-magnetic moulds.
Then the discs and the small blocks of soil attached beneath them are carefully removed.
The direction and magnitude of the magnetic field of the Earth at a particular location varies with time, and can be used to constrain the age of materials.
In conjunction with techniques such as radiometric dating, the technique can be used to construct and calibrate the geomagnetic polarity time scale.
The pole moves around, but magnetised deposits stay fixed on its position at the time of burning.
We can measure the difference between their orientation and the present position of the pole, which can give us the date of the burning episode.