What do scientists think happens in the core to produce the Earth's magnetic field? The liquid iron and nickel outer core's motion in relation to the metallic solid inner core becomes a geodynamo.

The outer liquid core becomes magnetized by the rapid spin of the solid inner core.

The solid inner core of iron and nickel acts as a large magnet.

The liquid iron and nickel inner core's motion in relation to the mantle become a geodynamo producing a magnetic field.