Earth's Magnetic Field

Nine times in the past 4 million years, Earth's magnetic field was exactly the opposite of its present polarity.

Declination, also known as magnetic declination, is "the clockwise angle from true north assumed by a magnetic needle." Declination also varies from place to place on Earth's surface. This observation means that the directions of the magnetic lines of force must also vary from place to place. Historic variations in the magnetic field provide strong additional evidence in favor of the idea that only in a liquid could such rapid wobble occur. I don't totally understand the explanation, but in sedimentary rocks, they tend to orient themselves parallel to Earth's magnetic field as they settle through water - an entirely different process than what happens with igneous rocks. In either case, the magnetic strength in these rocks is weak, but not so that it can not be measured accurately. In addition, because rock magnetism normally does not change with time, geologists can identify the declination (and inclination) of Earth's magnetic field at the time the rock formed. The caveat is the provision that the rock has not changed its position.

Yet, the continents move when the plates of the lithosphere move. Therefore, ancient rocks may not today be in the position (relative to the magnetic poles) that they occupied when they became magnetized. The measurements must be viewed as a record of the continents moving relative to the magnetic poles rather than vice-a-versa.

Fluid motions in the Earth's outer core cause our Earth's magnetic field. The position of the magnetic field varies with time. Nine times in the past 4 million years, Earth's magnetic field was exactly the opposite of its present polarity. Last, but not least, and the scariest to me, this magnetic field acts as a giant shield that protects us from the streams of ionized particles given off by the Sun. That stream is known as the solar wind. The shield that protects us from the solar wind is Earth's magnetism. When the magnetic field is reversed, the magnetic shield is not there to deflect this lethal solar wind.

Copyright © 2008 Craig B
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