A review on rock magnetism

Crustal rocks have a magnetic memory that may endure for millions or even billions of years due to composition of iron oxides The secret behind that permanence lies in the high temperatures to which the minerals were exposed near their Curie temperatures of several hundred degrees Celsius while cooling in Earth rsquo s magnetic field and in the stabilizing influence of the cooling process itself This memory is known as thermal remanent magnetization TRM It is much more resistant to subsequent fields than the more conversant remanent magnetization due to fields applied at ambient temperatures in a computer rsquo s hard drive for example Still a small fraction of the TRM responds to and records Earth rsquo s field during later heating events such as the burial of the rocks during mountain building plate subduction nbsp