If you have ever used a compass, you know that it can be used to navigate. it does this with a needle that always points north, so you know which direction you are heading. the needle points to the north because the earth is like a giant magnet, with both north and south poles. according to current theory, the creation of earth's magnetic field is closely linked to a) particle interactions in the ionosphere b) seismic collisions within the earth's crust c) the flow of molten iron under the earth's crust d) the flow of ocean water under the earth's crust