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تاريخ التسجيل : 11/05/2015
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Development of the Magnetosphere

في الأحد مايو 17, 2015 4:37 pm
Development of the Magnetosphere


The loss of heat from Earth’s exterior allowed its interior structure to

develop. As molten iron solidified, it created the dense, solid inner core

at the center of the planet. The core has remained solid because of

enormous pressures. The outer core is liquid. Motion in the iron-rich outer

core continuously generates electrical currents. This in turn produces

Earth’s magnetic field. You may recall from physics classes the effect of

rotating a bar magnet through an electrical field. A similar effect occurs

in Earth’s core. It is called the dynamo effect. Earth’s magnetic field is

self-sustaining. It is able to maintain itself.

The magnetic field shields Earth from the solar wind. Without the

magnetic field, the constant stream of particles from the Sun would

have eroded Earth’s atmosphere. It would be lost into space.

When igneous rocks cool, magnetic minerals record the direction and

strength of Earth’s magnetic field. Rocks from the Kaapvaal Craton in

South Africa are 3.5 billion years old. They indicate the presence of a

magnetic field early in Earth’s history. Earth’s magnetic field moves in

a complex pattern. The geologic record shows that the magnetic poles

have reversed many times. The last time was 780,000 years ago.
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