This was a question that came in a exam. How come is this possible?
Actually, a question on the source of Earth's magnetic field was asked here on physics SE, which matches my opinion.
The source of Earth's magnetic field is the molten iron and metals in the earth's core. The spinning of these liquid metals produces the same effect as electric current in a coil which produces a magnetic field.
Yes, that is true. Circulating ions of iron and nickel in a highly conducting liquid of Earth's core forms current loops and produces a magnetic field.
There is something to do with geologist though I'm not getting it. How come geologist doesn't seem to agree with this?
Answer
The magma has temperature between 700 and 1300 Celsius degrees. The Curie temperature of iron is at 770 degrees Celsius. Above that temperature, iron loses magnetism. Note that right above 770 °C, iron is still solid because the melting point is around 1500 °C.
So magma almost never can be magnetic because it's just too hot for that. Incidentally, if it gets melted and then refreezes, it typically doesn't regain magnetism. The situation is even clearer for Earth's core whose temperature is 6000 °C or so. There can't be any magnetism for iron and nickel that is this hot.
Geomagnetism is driven by the dynamo effect which is a loop of magnetic loops creating currents and vice versa that is partly being sustained by radioactivity.
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