Translations of Encyclopedia about Geology

Earth's magnetism

The earth is surrounded by an extensive magnetic field. This magnetosphere extends far into the universe and protects the earth against the solar wind.

The magnetic field that is measured at the earth's surface is, on one hand, the result of the flow of molten metal in the outer core of the earth (permanent field) and, on the other hand, the consequence of fields caused by the flow of electric particles in the ionosphere (the upper layer of the earth's atmosphere) and the magnetosphere. We can visualise its lines of force as enormous loops irradiating from the earth's magnetic poles. These are situated near the geographical north and south poles (today they are separated by approximately 11 degrees).

The first magnetic field of the earth may have originated when the earth, as a whirling mass of gas and dust many million years ago, brushed against the magnetic field of the sun. This would have magnetised the electrically conductive material in the earth's mass and activated the electrons (particles), which in turn during their travels produced current, creating at the same time the earth's magnetic field proper.

In 1600, William Gilbert, naturalist and personal physician of the English Queen Elizabeth I, published his hypothesis that the earth may be compared to a gigantic magnet. However, the action of the earth's magnetism had been known long time before that and it was used for orientation with compass.

Naturally, there is no magnetic rod in the earth's interior, although we might make such a comparison when we consider the magnetic field. It has opposing poles and is therefore called a bipolar field.

The magnetic north pole and the magnetic south pole are not identical with the geographical poles, because this bipolar field is tilted vis-à-vis the rotating axis of the earth approximately by eleven degrees. The magnetic needle of the compass thus indicates only an approximate direction of the north and the south.

The magnetosphere, which is the space occupied by the magnetic field, is heavily deformed by the solar wind. When these solar particles hit the magnetic field, they create a shock wave and depress the field. On the day side, the magnetosphere is between eight and ten times larger than the radius of the earth. On the night side, it extends high above the lunar orbit (more than 1000 x the radius of the earth). Within the earth's magnetosphere is an annular flow.

The majority of the solar wind particles are trapped the earth's magnetic field and deflected into the space around the earth. Some particles travel to the upper layers of the atmosphere – the ionosphere. When they come in contact with oxygen and nitrogen, these gases emit light creating the so-called northern lights.

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