Dating methods based on the fact that the magnetic north pole wanders around the rotational north pole and has repeatedly reversed position with the magnetic south pole at irregular intervals in the past. There are permanent records of these movements in the form of thermoremanent magnetism found in burned clay and rock as well as geological deposits of volcanic origin. Archaeomagnetic dating is the term generally used for dating based on the wandering of the magnetic north pole around the rotational north pole over the last 10,000 years or so. Geomagnetic reversal time scale (GRTS) dating and geomagnetic polarity time scale (GPTS) dating are terms applied to the method based on the much longer term reversals of the magnetic poles. The two related paleomagnetic dating methods have been considered by some researchers to be chronometric and calibrated relative by others.