Earth’s magnetic field has always been a matter of interest
for scientists all over the world. However, unlike the field of a bar
magnet, Earth's field changes over time because it is generated by the motion
of molten iron alloys in the Earth's outer core.
Earth's polarity is not constant. Unlike a classic bar
magnet or the decorative magnets on your refrigerator, the matter governing
Earth's magnetic field moves around. Geophysicists are pretty sure that the
reason Earth has a magnetic field is because of its solid iron core is surrounded
by a fluid ocean of hot, liquid metal. This process can also be modeled with
supercomputers. Ours is, without hyperbole, a dynamic planet. The flow of
liquid iron in Earth's core creates electric currents, which in turn create the
magnetic field. So while parts of Earth's outer core are too deep for
scientists to measure directly, we can infer movement in the core by observing
changes in the magnetic field. The magnetic north pole has been creeping
northward – by more than 600 miles (1,100 km) – since the early 19th century,
when explorers first located it precisely. It is moving faster now, actually,
as scientists estimate the pole is migrating northward about 40 miles per year,
as opposed to about 10 miles per year in the early 20th century.
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