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Experts on the Earth's interior met this week to battle out one of their unsolved questions: what is the temperature of the Earth's core? The answer could shed light on how the Earth formed, on earthquakes and continental drift, and on the Earth's magnetic field.

Earth scientists, meeting at the Royal Society this week, presented the results of two rival methods of working out the inner temperature of the Earth. Both involve recreating in the laboratory the conditions thought to be present in the Earth's mainly iron core, where the pressure is about three million times that on the planet's surface.

European groups, using the "diamond-anvil" cell, made estimates of 4,800 degrees kelvin. Their method recreates the conditions 3,000 kilometres into the Earth. A tiny piece of pure iron is sandwiched between two diamonds and bombarded with infrared radiation. The iron absorbs the radiation and its temperature rises to several thousand degrees. Then the temperature at which the iron melts is recorded.

Meanwhile, some American scientists claim that the Earth's core is about 6800K. In their "dynamic shock wave studies" an object accelerates to several kilometres a second, hits a thin piece of foil which generates a high pressure shock wave. Optical methods work out the resulting temperatures.