Here’s an interesting article about the source of Earth’s magnetic field – “Earth’s inner core is doing something weird” by Maya Wei-Haas. Back in the 70s, the Soviets tested some huge atomic bombs. The shockwaves bounced off the Earth’s core and were picked up by geologists in Montana. Recently, scientists revisited the data and have concluded that the core spins just a little bit faster than the surface (and presumably the mantle). They further speculate that this disparity in rotational velocity is exactly what’s needed to generate the dynamo that causes Earth’s magnetic field. I completely agree. But even more than that, if it doesn’t rotate at the same speed, it also very likely doesn’t rotate on the same axis. In the Pulsar section of my book I noted that:
It is more likely that the Earth’s [magnetic] field is the result of the iron core not rotating in exactly the same plane as the mantle. That is, the solid core of our planet does not track the precession of the axis of the liquid mantle and thin crust, but instead continues rotating in the same plane no matter what the rest of the planet does.
The Substance of Spacetime, Chapter 4: Astrophysics, Pulsars
If the core and the rest of the Earth rotate on different axes, then it is likely that the core maintains the same axis over the Earth’s entire life, while the mantle and crust wobble as its mass shifts around due to tectonic plate movement, mantle convection, and less frequently, large bolide collisions. Such wobbling might help explain the precession of the axis, the 26,000-year rotation, or wobble, of the rotational axis, as well as other variations in the magnetic field.