Fig. 1

a The structure and magnetic inclination lines for a “normal” (e.g. north-seeking) geocentric axial dipole. The spin axis of the Earth is coincident with the magnetic dipole. b The structure and magnetic inclination lines for a “reverse” (e.g. south-seeking) geocentric axial dipole. The spin axis of the Earth is coincident with the magnetic dipole. c The relationship between magnetic inclination and latitude for both Normal (N) and Reverse (R) magnetic fields. As an example, the magnetic inclination at 60 degrees north in a normal field will be ~74 degrees. d1 Hypothetical sampling location on North America. The measured ancient declination in the rock is shown by the arrow and the measured ancient inclination in the rock is given as I = 0 in this example. 2 Reconstruction of the continent, assuming a normal magnetic field existed during formation of the rock. Notice how the arrow now points to the north and the sampling location is positioned at the equator according to the dipole formula. 3 Reconstruction of the continent, assuming a reverse magnetic field existed during the formation of the rock. Notice how the declination now points due south and the sampling location is positioned at the equator according to the dipole formula