Magnetic fields that are altered or formed in atoms of iron by heat in excess of 1100° F. (600° C. ). Such fields line up with the magnetic field of the planet at the time of the exposure to a high temperature. They will remain oriented to that direction indefinitely despite the fact that the true position of magnetic north wanders over thousands of miles around the rotational north pole and even reverses with the magnetic south pole over longer periods of time. See paleomagnetic dating.