This isn't my area of expertise, but my high-level lay understanding is the core is spinning at a rate faster than the crust. I suppose when it all slows down

This isn't my area of expertise, but my high-level lay understanding is the core is spinning at a rate faster than the crust. I suppose when it all slows down and the spin rates from core to crust converge, it will all settle down and cool. But I think that's also when you lose the magnetic field... Would love for someone better versed in earth's geophysics to chime in!