Why Does the Earth Have a Magnetic Field?

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Earth has a magnetic field because of the iron-rich core that rotates very slowly beneath the surface. Get interesting information on experiments used to determine why Earth has a magnetic field, and how the magnetic poles can switch, from a math and science teacher in this free video science lesson.

Part of the Video Series: Science & Environmental Facts
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Video Transcript

Hi, I'm Steve Jones and I'm going to explain why the earth has a magnetic field. Well, actually, I'm going to explain it in simple terms because really people don't actually know why they magnetic field appears as it does. And to explain the phenomena that we get with the earth, it's quite complex. But I'll basically describe the structure first of all. The earth is in various shells. The outer shell, the crust upon which we stand at the moment is not very thick. It's a couple of kilometers thick. In places it's thinner. In other places it's thicker, depending on whether there's mountains and so forth. So, there is a thin crust on the surface. Underneath this people often think that there is a molten area. Well, that is certainly not the case. This is not molten. It is not a liquid. It is a very very sticky solid. It moves very very slowly and that's what causes the fractures in the surface and volcanoes and things like that. Underneath there is a lower mantle. Slightly different structure, but similar material. It is the core that we believe to be liquid and people have done experiments on materials that they think the core is made of. They believe the core contains quite a high proportion of iron and obviously where there is iron, you expect magnetism. But the core is liquid and it is believed that there is a rotation within that central core of liquid which produces the earths magnetism. But whatever happens the earth's magnetism appears in this core. Recent experiments have tried to show why the earth's magnetism has changed. Because at the moment the earth's magnetism is as if you had a magnet in the center with the north pole down here and the south pole up there. This is the actually, magnetic north pole here. So, at the moment, it looks as though we think that it is like this. There is some kind of, not physically a magnet, but there is something that produces a property as if there were a bar magnet in the center of the earth. There isn't. It's just rotating fast, rotating liquid material we believe. When this experiment was tried in a laboratory, they found that there were sudden changes so that this could suddenly from north to south this way to north to south the other way. So the experiment in the laboratory actually explained why in the past the earth's magnetic field has not always been north here and south there. In fact it was south and north here. So there have been those developments over a period of many thousands of years and it does tend to flip the magnetic field and the magnetic field basically comes from the core of the planet. This iron rich core of the planet. So that's why the earth has a magnetic field.

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