Hey Tech, good to see you, but I have to contradict a few of your statements:

"What makes a volcano erupt? Or an earthquake? Movement in the hot molten core.
And what triggers that movement? What causes the heat in the first place?"

Movement in the hot molten outer core (the inner core is solid) does not make volcanos erupt nor seismic events. Felsic volcanos, like the Cascades or the Andes have their origin in the partial melting of the lower crust above subduction slabs. Rift volcanos are basalt that rises from the asthenosphere due to a weakened crust. Ocean ridge volcanos are the result of upwelling asthenosphere material. Hot spot volcanos are the results of plumes in the mantle, but the material is mostly from the asthenosphere melting lower crustal rocks. The only volcanos that have a material origin in the mantle are carbonotites, (and they are mostly from the early history of earth), and kimberlites (which contain true mantle material like diamonds). Now it is true that convective currents in the mantle are driven by the heat engine below in the core which in turn drive plate tectonics. But it is the heat of the core, not the movement. (although there is some evidence that the inner core does have convective currents, but they are decoupled from the mantle currents. Likewise, earthquakes are restricted to the crustal material. Earthquakes happen in cold brittle rock, not hot ductal material. On mars, volcanos erupted even after the core cooled and could no longer move nor create an effective magnetic field. Not sure how that fits in with your model.

While it is true that the movement of the outer metallic core is the dynamo that create our magnetic field that shields us like a blanket, the movement is not responsible for plate tectonics.

Furthermore, it is radioactive decay that is the heat source for the inner core. Not the sun. Seriously? I'd love to see a peer reviewed article that supports your thesis. Sounds like the Electric Universe pseudoscience we used to endure here.

It appears that a magnetic polar shift occurs when a new dipole develops at an acute angle to the established dipole. It has to do with the evolution of semi-chaotic vortices in the magnetofluid of the outer core. You like vortices, don't you? The overall magnetic field does not vanish completely. I have never seen a study that successfully correlated extinction events with pole reversal. Again, if you have a reference for me, I'd be happy to evaluate it.

Nice to see you posting, hope the time travel is going well. Cheers.