Which mechanism explains the existence of Earth's magnetic field?

• A. The movement of the liquid iron-nickel outer core generates the magnetic field.
• B. Rotation-induced gravity creates the field.
• C. Magnetism is a property of the crust only.
• D. The atmosphere's wind shapes the field.

Answer: (A)

Earth's magnetic field comes from dynamo action in the planet's liquid outer core. The outer core is a highly conductive melt of iron and nickel, and heat-driven convection there causes movement of this conductive fluid. As these electrically charged motions occur in a rotating frame, the Coriolis effect twists them into organized, swirling currents. Those currents generate electric currents, and the resulting magnetic field is sustained by this self-exciting process, producing the large-scale field that extends from the core into space. The crust can hold its own magnetization in some rocks, but it does not drive the global field. Wind in the atmosphere doesn’t shape or generate the field either. So the best explanation is the motion of the liquid iron-nickel outer core generating the magnetic field through a geodynamo.