Intensity of the Earth's Magnetic Field in Geological Time

Thellier's Method was applied to rocks obtained from several volcanic formations in Japan, of which geology has already been studied in detail. Owing to unstable nature of remanent magnetization and other effects in heating experiments, most of the Pliocene rocks did not give any meaningful results. Samples from Pleistocene lavas show more favorable behaviors in experiments. In all, 9 Pleistocene and 4 Pliocene intensity values were obtained. Of these, Pliocene values except for intermediate polarity are nearly the same as and Pleistocene values are much larger than the present magnitude of the geomagnetic field.