The Earth could be about to turn upside down. The planet's magnetic field is showing signs of wanting to make a gigantic somersault, so that magnetic north heads towards Antarctica, and magnetic south goes north. Compasses will point the wrong way, and migrating birds, fish and turtles are going to be very confused.

Just when this will happen, how long it will take and what the consequences will be, is difficult to fathom. What is not in doubt, though, is that it will happen. About every half a million years or so, the Earth's magnetic field flips upside down.

Earth`s magnetic poles are constantly drifting around. At present, magnetic north is heading out of Canadian territory into the Arctic Ocean at about 10 miles per year. Also, a bar magnet quickly loses its power, yet the Earth's magnetic field has been around for billions of years, so something is regenerating it. This is why Einstein remarked that the origin of the Earth's magnetic field was one of the greatest mysteries of physics.

Magnetism trapped in ancient pottery shows that over the past 4,000 years, the magnetic field has weakened by more than 50%. This past century, the strength has dropped by 5%. At this rate, the field might disappear in the next few hundred or thousand years. Another warning sign of an imminent flip has come recently from satellite measurements of the Earth's magnetic field.

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