10.4 How do we know ... Earth's core is a dynamo?
Fig 10.17
Interestingly, the Glatzmaier-Roberts simulations reversed the magnetic field during the course of the simulation. This too is consistent with geologic thought on the geodynamo. It is thought due to interactions of the magnetic field with the inner and outer cores. The temporary magnetization of the hot, solid inner core is more stable in direction and tends to resist reversal. However, every so often (on the order of tens to hundreds of thousands of years), it does succeed.