Test of the dipolar nature of the geomagnetic field throughout Phanerozoic time

Abstract

THE morphology of the geomagnetic field throughout the Earth's history is of interest first, in a general way, to geomagnetists in terms of long term implications concerning the Earth's core, its thermal regime and the motions in it, and, second, in a very particular way, to palaeomagnetists since the geocentric dipole model is universally used in mapping observed field directions into palaeomagnetic poles. Runcorn^1,2 has given strong reasons for supposing the mean geomagnetic field to be symmetrical about the Earth's spin axis. He has also argued³, on the basis of early palaeomagnetic data, that a dipolar field coupled with continental motion is preferable to higher order axial multipole fields. Here I discuss an observational test, based on the much larger body of palaeomagnetic data now available, to discriminate between a dipole field and those of higher order multipoles.