MAGNET EARTH
The Earth's magnetic field has guided travellers for centuries. But it is far more crucial to life on the planet than simply a navigational aid. The field extends into space around the planet to form the magnetosphere, protecting us from charged particles in the solar wind. These are deflected to the poles and can be seen as aurorae. If the solar wind particles were free to rain down on the Earth it would be very bad news for life as we know it. Could Earth lose it's magnetic field and the protective magnetosphere?

The Earth's magnetic field is not an easy subject to study as it is generated deep within the centre of the planet. To probe to such depths, at incredibly high temperatures and phenomenal pressure is just not possible. Information about the field is gathered in other ways - lab and computer simulations of the Earth's centre, satellite observations and geophysical studies of rocks.

We know the heart of the Earth is an iron core about three quarters the size of moon, maintained as a solid at a temperature up to 7000c by extreme pressure. The outer layer of the core is molten iron which is surrounded by the 2900km of solid mantle. The Earth's crust is only about 30km thick.
The Earth has a North and South exactly like a huge permanent bar magnet. However this cannot be so as iron loses its magnetism at 77c.

It is widely believed the Earth's magnetic field is generated by the motion of the molten iron core. Behaving like an electric generator to create a magnetic field. This is known as the Earth's geodynamo. Two forces cause motion and turbulence in the fluid iron. Convection generated by the extreme heat of the planet's core and the Coriolis effect (the deflection of objects from a linear path due to the rotation of the planet). These forces have sustained the geodynamo for billions of years.

French scientists are very close to demonstrating the nature of the geodynamo in the laboratory. They have created a self-sustaining magnetic field in liquid sodium, which has similar properties to iron. At the University of California, Professor Gary Glatzmaier uses 3D computer models to study the Earth's interior. The scientists agree that the exact nature of the force driving the flow in the core is unknown. Some believe it is convection, some believe it may have something to do with a tidal mechanism.

The magnetic field may reach its saturation point but scientists do not know when or at what magnitude. Bigger lab experiments and more powerful computer models should give these answers in the future.

And the answer to our original question is yes the Earth could lose its magnetic field; the French team found that a rise in their ‘molten core' temperature decreased its electrical conductivity and thus stopped the generation of the magnetic field. Likewise as the Earth cools the liquid core becomes smaller as it solidifies onto the solid core. One day there may not be enough liquid core to generate a magnetic field.

However it is likely that the geodynamo is good for a billion years or so, and Earth will continue to be protected by its magnetic umbrella.