Since the iron at the Earth's core is hotter than the Curie temperature, it cannot hold a permanent field, but may help to stabilize this process, which it helps perpetuate through convective motions given rise to by Earth's rotation.
In 1934, Thomas Cowling proved that no self-sustaining one could have an axis of symmetry, and Stanislaw Braginsky obtained valid solutions for it by assuming that the field it produced was almost axially symmetric. Thermal convection cannot drive it because it would require temperatures that were too high, but compositional convection can help. Since the iron at the Earth's core is hotter than the Curie temperature, it cannot hold a permanent field, but may help to stabilize this process, which it helps perpetuate through convective motions given rise to by Earth's rotation. FTP, identify this inductive effect which attempts to explain why the Earth has a permanent magnetic field.
In 1934, Thomas Cowling proved that no self-sustaining one could have an axis of symmetry, and Stanislaw Braginsky obtained valid solutions for it by assuming that the field it produced was almost axially symmetric.
dynamo effect (or theory or whatever)