If freely suspended, one pole will point toward the north. The two poles are thus named the north magnetic pole and the south magnetic pole or more properly, north-seeking and south-seeking poles, for the attractions in those directions.
Figure 2. One end of a bar magnet is suspended from a thread that points toward north. Figure 4. North and south poles always occur in pairs. Attempts to separate them result in more pairs of poles. If we continue to split the magnet, we will eventually get down to an iron atom with a north pole and a south pole—these, too, cannot be separated.
The fact that magnetic poles always occur in pairs of north and south is true from the very large scale—for example, sunspots always occur in pairs that are north and south magnetic poles—all the way down to the very small scale.
The old fellow does value his privacy, after all. Register or Log In. The Magazine Shop. Login Register Stay Curious Subscribe. Planet Earth. Newsletter Sign up for our email newsletter for the latest science news. Sign Up. Already a subscriber? Want more? More From Discover. Recommendations From Our Store. Other electromagnetic anomalies can be seen all over the world, such as in southern Africa where a magnetic field disturbance, similar to an eddy in a stream, may be caused by a denser portion of the mantle near the boundary with the planet's liquid outer core.
While the poles are constantly shifting, they have also completely reversed at least a few hundred times within the last 3 billion years, according to NASA. During this process, which typically occurs every , to , years over the course of to a few thousand years at a time, the magnetic field becomes squashed and pulled with multiple poles sprouting up randomly over the surface of the Earth.
The last full reversal occurred about , years ago. The history of the magnetic field, including shifts and reversals, is evidenced in the geologic record. Metals found in rocks, including iron, align with the magnetic field before molten rocks solidify or as fragments that contain the magnetic metals aligned with the magnetic field and settle in layers of sedimentary rocks. Similar records are found on the floor of the Atlantic Ocean where new seafloor is constantly being created at the mid-Atlantic ridge.
As the lava solidifies, it locks the metal deposits in place, and thus, creates a historic record of the shifts and reversals of Earth's magnetic field. That's not the end of the story, of course. The magnetic poles have not remained in the same place. So both declination and inclination have wandered.
The Earth's magnetic field is not static. A Physics Narrative presents a storyline, showing a coherent path through a topic For 17 Resources. Classroom Activity
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