Palaeomagnetics is the study of Earth's remnant magnetism preserved in rocks that contain magnetic minerals, in particular the iron-rich mineral called magnetite. Over time these rocks acquire a weak but permanent magnetism during crystallisation, deposition, or cementation of the minerals. The orientation and polarity of this preserved remnant magnetism has been shown to be aligned parallel to the Earth's ancient magnetic field that existed at the time of preservation.

The data used in this section of the Expansion Tectonic small Earth modelling is based on the Global Palaeomagnetic Database — Ver. 4.6 published in 2004, available from the National Geophysical Data Centre (NGDC): www.ngdc.noaa.gov/geomag/paleo.shtml

The primary role of palaeomagnetic studies carried out on samples of magnetised rock is to provide measurements in order to determine the ancient latitude of the sample site and to measure a direction and distance—established from the colatitude—to the ancient magnetic pole. In conventional studies, based on a static radius Earth model, the location of the ancient pole can then be calculated.

To minimise errors during sampling of the magnetised rock under study, and to give a more statistically representative measurement, a series of samples are generally taken for each sample site. These samples are structurally corrected to compensate for any Earth movements that may have occurred to the site since deposition of the rock sample. They are also magnetically screened for any overprinting magnetic vectors, such as the effects of metamorphism, which may have occurred since initial preservation.