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Last Updated: Wednesday, 28 January, 2004, 14:19 GMT
Earth's core 'simpler than thought'
Scientists working on efforts to understand the Earth's centre have made a surprising discovery: the iron core is actually much simpler than they had assumed.

Planet Earth
The core generates the Earth's magnetic field
Researchers at the US Lawrence Livermore Laboratory who have been studying how the enormous pressure inside the planet affects the iron believe there is only one form of atomic structure to the metal.

For the past 20 years, it has been assumed there were at least two.

The scientists are hopeful that by cracking the structure of the core, they can understand better the temperature and pressure there. They have already established the core starts to melt at a lower pressure than previously thought.

Their work has recently been published in the journal Nature.

"It makes the picture a whole lot simpler," Dr Neil Holmes, one of the scientists who worked on the project, told BBC World Service's Science In Action programme.

"It allows us further to focus our efforts... determining the temperature and the other properties of iron."

Huge pressures

The Earth's core is important because it generates the planet's electromagnetic field - which seems to be weakening.

This is already having consequences in space, creating glitches in satellites that rely on the field to protect them from solar and other space radiation.

Furthermore, scientists are keen to find out if the Earth's magnetic poles are about to "flip" - with magnetic North becoming South, and vice versa. It has happened many times before in Earth history.

Dr Holmes said the key to the experiment was recreating conditions that were as close as possible to those that really existed at the centre of the planet.

"We have a large gun which is 20 metres long, which fires flat, iron-faced projectiles into an iron target, making a shockwave," he said.

"That shockwave only lasts for less than a millionth of a second, but during that time we can make conditions that are up to and even exceeding the pressures at the centre of the Earth."

Specifically, what the scientists have found is that the iron adopts a crystalline structure, like a diamond, in the Earth's core.

The Californians are not the only researchers interested in what is effectively a massive dynamo at the centre of the planet driving the geomagnetic field.

Scientists in Riga at the Institute of Physics at the University of Latvia are continuing to work on a much more physical mock-up of the core.

Their model consists of two concentric steel cylinders, three metres high and 80 centimetres in diameter, filled with molten sodium.

A propeller drives the sodium down through the inner cylinder in a helical flow.

The metal returns up the outer cylinder, and electric currents create a magnetic field.

"Sodium has - by a factor of 50 - better electro-conductivity," the University's Dr Agris Gailetis told Science In Action. "Sodium is moving 10,000 times faster.

"But of course our system is much, much smaller... but altogether, these factors are making our experiment not very different from conditions inside the Earth."

'Turbulent regime'

However, bizarrely, the oscillations that the Riga experiment have produced have been found to be more like the regular 22-year-variations in the Sun, rather than the random ones in the Earth.

The reality of the core remains far more complex than concentric cylinders. The flow there is probably turbulent and chaotic.

"The Riga experiment didn't, per se, undergo reversal," said Dr Andy Jackson, who specialises in computer models at Leeds University in the UK.

"But it does generate a magnetic field which is oscillatory - but it's oscillatory in a very regular sense, whereas the Earth is more of a random process."

Dr Jackson outlined the way that such experimental geophysics helps us understand our planet.

"In the last decade we've made great advances in using numerical simulations to understand planetary magnetic field generation," he said. "But there are some real drawbacks with these computations.

"For example, it's almost impossible for us to model turbulent flow. There's a place for the experiments to try to fill in the gap that's left by the numerical simulations.

"The experiments really can reproduce this turbulent regime that's so important in the core."


SEE ALSO:
Earth loses its magnetism
31 Dec 03  |  Science/Nature
Plumbing the Earth's depths
14 May 03  |  Science/Nature
Is the Earth preparing to flip?
27 Mar 03  |  Science/Nature
Quakes reveal 'core within a core'
02 Oct 02  |  Science/Nature


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