A chronometric method used to date objects containing magnetic materials - especially for buried undisturbed features such as pottery kilns, earthen fireplaces, and brick walls - which can be compared to known schedules of past magnetic alignments within a region and fluctuations in the earth's magnetic field. Clay and rocks contain magnetic minerals and when heated above a certain temperature, the magnetism is destroyed. Upon cooling, the magnetism returns, taking on the direction and strength of the magnetic field in which the object is lying. Therefore, pottery which is baked in effect fossilizes the Earth's magnetic field as it was the moment of their last cooling (their archaeomagnetism or remanent magnetism). In areas where variations in the Earth's magnetic field are known it is possible to date a pottery sample on a curve. This method yields an absolute date within about 50 years.