Migration of the magnetic poles of the Earth through geologic time.
Scientific evidence indicates that the magnetic poles have slowly and erratically wandered across the surface of the Earth. Pole locations calculated from measurements on rocks younger than about 20 million years do not depart from the present pole locations by very much, but successively greater "virtual pole" distances are revealed for rocks older than 30 million years, indicating that substantial deviations occurred. Calculations of polar wandering formed one of the first important pieces of evidence for continental drift .