Listening practice: The map that follows magnetic north

A compass looks simple. A needle turns, settles, and points you toward north. But the north it follows is not the same as the North Pole on a map. According to the British Geological Survey, Earth's magnetic field is generated mainly by slow motion in the liquid iron of the outer core. That field reaches the surface, passes through rocks, oceans, cities, and the phone in your hand, and gives a compass its direction. The important detail is that the field is alive in a slow way. It changes over years. Magnetic north wanders, and a compass reading that was correct in one decade may need a different correction later.