Earth's magnetic field swapping poles?

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But the way minerals are aligned in ancient rock shows that the planet's magnetic dipole occasionally disappears altogether, leaving a much more complicated field with many poles all over the planet. When the dipole comes back into force, the north and south poles can swap places.

The last reversal happened about 780,000 years ago, over a period of several thousand years. Now Gauthier Hulot from the Institute of Earth Sciences in Paris and his colleagues think they have spotted early signs of another reversal.