Evanston, Illinois - The Earth's magnetic field, long thought to be generated by the planet's molten core, may instead be produced by ocean currents.
Movement in a conducting liquid generates electricity and magnetism, and the accepted theory has been that it's the swirling molten metal at the Earth's core that is responsible. But according to research from Northwestern University it's actually seawater - which is conductive because of the dissolved salt - that produces the effect.
With observational evidence of the Earth's core so difficult to obtain, scientists have tended to rely on computer modeling - but this has thrown up inconsistent results.
Northwestern researchers took a different approach, looking at the variations in the planet's magnetic field. This is constantly fluctuating, with magnetism growing stronger or weaker in different places, and with the poles gradually shifting over time.
They found that these variations correlated strongly with changes in ocean circulation. In the north Atlantic, for example, changes in the strength of currents were matched by sharp changes in magnetic fields.
The researchers suggest that changes in ocean circulation may even be responsible for the reversals in the Earth's magnetic field, in which the north and south magnetic poles suddenly swap over. Movement of tectonic plates would dramatically alter ocean currents, and could have led to the last 'flip' around 780,000 years ago.
One implication of the findings is that climate change - which is now being seen to alter ocean currents - could also have an effect on the Earth's magnetic field.
The findings are published in the New Journal of Physics.