While humans have been trying to find their way around and then find their way back for eons, the simple navigational aid known as the compass wasn’t invented by the Chinese until around 200 BC. What took so long? Did it have anything to do with the fact that Earth once had multiple magnetic poles that would have driven compasses, sailors and nomads crazy?
It actually happened a lot earlier that 200 BC, according to Peter Driscoll, a researcher at the Carnegie Institution of Science and author of a new study in the journal Geophysical Research Letters. While studying geothermal records going back 4.5 billion years, he noticed massive fluctuations in magnetic field directions and numbers beginning around 650 million years ago. The cause of these fluctuations required a change in thinking.
The north and south poles are where they are because of the Earth’s molten iron core rotating around a solid inner core. Laboratory models and simulations of this have been consistent in showing a “stable dipole field” – two poles at either end. So what caused what looks like multiple poles 650 million years ago?
Driscoll speculated that this might be when the Earth’s core went from completely liquid to having a solid inner core. Feeding that idea into existing models and into new 3-D dynamo simulations, which model the generation of magnetic fields by strong fluid motions, Driscoll found that Earth had two poles a billion years ago, went to multiple poles around 600 million years ago and then back to the current two poles some time after that.
While having two poles to control our compasses is nice (at least when you can’t get a GPS signal), the real benefit of Earth’s magnetic field is protecting the planet from cosmic radiation. If the multiple-pole theory holds true, it could explain severe climate fluctuations during the Neoproterozoic Era when the so-called Snowball Earth period – a near-frozen era of global glaciations – is believed to have taken place.
It looks like you should continue to use your GPS to keep from getting lost but keep a compass around to warn of glaciers, magnetic field fluctuations and more.