Sir William Gilbert hypothesized in the late 1500s that Earth acts as a giant magnet, explaining why compasses point north. While Earth's core is too hot to be the source of magnetism, the circulation of molten material in the core is related to Earth's magnetic field. Earth's magnetic poles are located in northern Canada and Antarctica, differing from the geographic poles. Earth's magnetic field can magnetize ferromagnetic materials like iron over long periods of time.