Continental drift, seafloor spreading, plate tectonics: These terms conjure up a picture of the whole of Earth\u27s lithospheric plates in motion, a picture that truly represents a revolution in the earth sciences that took place in the 1960s and permanently changed our view of a more static world. If someone were to ask which subdiscipline of the geosciences has provided the crucial quantitative evidence about the past locations of discrete parts of continental and oceanic plates, the answer would be geomagnetism and paleomagnetism. Polarity stratigraphy, based on radiometrically dated 180° reversals of the dipolar geomagnetic field, informs us about the locations of parts of the seafloor in the past, and paleomagnetically determined paleolatitudes of continental rocks provide similar information about past locations of continental plates
