According to the theory of plate tectonics, the rocky plates that make up the Earth’s hard shell are constantly moving.
Strangely, the magnetic records of rocks formed at the same time seem to point to different locations for the poles. In this way, rocks lock in a record of the position of the Earth’s geomagnetic poles at that time. The particles line up along the lines of force in the Earth’s field. As lava cools and becomes solid rock, strongly magnetic particles within the rock become magnetized by the Earth’s magnetic field. The shifting locations of the geomagnetic poles are recorded in rocks that form when molten material called magma wells up through the Earth’s crust and pours out as lava. Earth’s magnetic poles often move, due to activity far beneath the Earth’s surface. The geomagnetic poles are not the same as the North and South Poles. The currents create a magnetic field with invisible lines of force flowing between the Earth’s magnetic poles. Scientists do not fully understand why, but they think the movement of molten metal in the Earth’s outer core generates electric currents. The field around the coil will disappear, however, as soon as the electric current is turned off. When electricity runs through a coil of wire, it produces a magnetic field. Some substances can be magnetized by an electric current. The force generated by the aligned atoms creates a magnetic field. When you rub a piece of iron along a magnet, the north-seeking poles of the atoms in the iron line up in the same direction. Opposite poles are attracted to each other, while the same poles repel each other. The magnetic field is the area around a magnet that has magnetic force. To become magnetized, another strongly magnetic substance must enter the magnetic field of an existing magnet. This makes the atoms in these substances strongly magnetic-but they are not yet magnets. In substances such as iron, cobalt, and nickel, most of the electrons spin in the same direction. That is why materials such as cloth or paper are said to be weakly magnetic. In most substances, equal numbers of electrons spin in opposite directions, which cancels out their magnetism. Their movement generates an electric current and causes each electron to act like a microscopic magnet. Spinning like tops, the electrons circle the nucleus, or core, of an atom. Each atom has electrons, particles that carry electric charges. Every substance is made up of tiny units called atoms. Magnetism is caused by the motion of electric charges. Magnetism is the force exerted by magnets when they attract or repel each other.
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