资源环境科技发展态势分析平台

By Michael Brooks

CAN you point to the north pole? Almost certainly not. Even if you are armed with a compass, you could easily get it wrong. If you are in California, your needle might be a full 18 degrees out. “You need to take account of that, even if you’re just hiking – it can be the difference between going left and going straight on,” says William Brown at the British Geological Survey.

It isn’t just that your compass can be thrown off by local quirks in the magnetic field. The north pole itself isn’t what it used to be. In 1900, the pole was in Canada. A century later, it was near Greenland. In the past 18 years, it has raced eastwards at about 40 kilometres per year, and is currently heading for Siberia.

The weird behaviour of Earth’s magnetic field doesn’t end there. It also occasionally reverses its polarity: there were times in our planet’s history when a compass needle pointed to what we call south. Even now, there are spots under the surface where a compass would point the wrong way. What is going on? The mystery has deep implications for technology and the future of our planet.

To address it properly, we would need to make like Jules Verne and journey to the centre of the Earth, where the field has its source. That isn’t exactly practical. Instead, inventive minds have sought out magnets frozen into the planet aeons ago and built giant spinning spheres of liquid sodium. All of which could help us better understand our …

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