What in the earth's interior allows us to use a compass?

Answer 1

The Earth has a magnetic iron core.

Actually, it isn't a magnetic 'core'. It is a magnetic deposit that is in the outer 20% of the earths mass. It is like a bubble of cherry juice under the crust of a pie baking. It moves around and slightly changes position over the years, but cycles back to it's prior position on a regular schedule. That is why magnetic north constantly moves back and forth. If you look at the 'magnetic declination', you will see how it changes from year to year. The Magnetic North Pole is actually some distance form the geographic north pole, north of the Hudson Bay. And by the way, the magnetic north pole is actually magnetically the south pole. If you have a magnet that is marked 'N' and 'S', suspend it from a string or place it in a floating saucer. The 'N' will point to the north, being attracted to the SOUTH (opposites attract) magnetic pole of the earth. Somewhere, this got reversed and no one wants to correct it.

(response) Allow me to quote from wikipedia: The Earth's magnetic field is mostly caused by electric currents in the liquid outer core. So, although it is the outer core, it is still the core. Not the outer 20% of the Earth's mass. Bear in mind, it is the core that is composed of highly conductive nickel and iron. The layer of magma in the mantle is not electrically conductive, therefore it would not support currents that could generate a magnetic field.

"mostly caused by electric currents in the liquid outer core" The liquid outer core as defined can be and probably is within the outer 20% of the earth's mass. "Inthe outer 20%" does not mean "is the outer 20%". The specific highly magnetic deposit that defines the earths magnetic field can be and is influenced by electrical current within the core or outer core as you wish. The magnetic deposit may not be totally magnetic on its own. Even as a nail in proximity of a pulsing electric current is not initially magnetic, it will become magnetised by the current, and eventually become magnetic because of the realignment of molecules within it. So yes, the current in the outer core causes or influences but is not the primary source of the earth's magnetic field.