Why did the earth a magnetic field? The electrical conductivity of molten plasma of the Earth's Core should be able to damp the current magnetic field only in thousands of years. But our five billion years old earth clearly causes magnets, to (defined) to the north. The secret is not known yet, but thought recently, in connection with earth movements in the liquid outer core. In particular, as parts of the outer core cool and fall inwards, oceans of liquid iron-rich magma to the outside world, forced to filter a helical motion by the spin of the earth. This movement, many geologists now believe that regenerates Earth's magnetism. In the picture above, a computer simulation shows the resulting magnetic field lines out to two Earth radii, with blue lines directed inwards and yellow lines directed to the outside world.