Long-term evolution of the geomagnetic dipole moment

The geomagnetic field intensity measured at the surface of the planet is a potential indicator of the dynamo activity in the conducting liquid core of the Earth. Rapid field variations must be generated by the rapid fluid motions within the core, whereas long-term changes could be associated with other processes such as changes in boundary conditions at the core–mantle interface and/or at the outer (liquid)–inner (solid) core boundary. For about 50 years, paleomagnetists gathered records of absolute paleointensity using the magnetization of lava flows distributed over the globe in order to reconstruct the field intensity changes during the past 3000 Ma. Despite recent acquisition of paleointensity records, the temporal distribution of the results remains limited (except within a few time intervals) to extract coherent features of the time-averaged field intensity over periods of a few million years. However, significant informations can be gained from the recent updated paleointensity database by averaging the virtual dipole moment over very long time intervals. The results suggest the existence of a long-term evolution of the dipole field intensity during the past 3 billion years (from 3 × 1022 A m2 at 1000–2000 Ma to 8 × 1022 A m2 at present times).