Testing the GAD throughout geological time

Abstract

The suggestion that the morphology of the geomagnetic field can be tested by inspecting the statistical distribution of palaeomagnetically-determined inclination angles has been challenged on the grounds that typical plate velocities require extremely long sampling intervals-perhaps exceeding the age of the Earth-in order to adequately sample the Earth's surface. Here, we investigate this problem by means of a random walk model and conclude that an interval equivalent to Phanerozoic time (600 Myr) is generally sufficient.

Dynamo tests for stratification below the core-mantle boundary

“…When averaged over separate polarity chrons, paleomagnetic inclination data indicate G30 0.01 during the Brunhes chron, but somewhat larger G30 0.05 during the Matuyama chron (Aubert et al, 2010). There is some evidence that G30 may have been far larger in the Precambrian (Evans and Hoye, 2007;Veikkolainen et al, 2014) but back then the influence of inner core buoyancy release may have been less or non-existent. Indeed, numerical dynamos with a passive inner core (Heimpel and Evans, 2013) or no inner core at all (Landeau et al, 2017) generally produce larger and more positive values of G30 compared to similar dynamos with an active inner core.…”