(Source: physics.org, nasa.gov)
Like football teams at half time, geophysicists think that the Earth’s magnetic poles could soon switch ends with the magnetic north pole becoming south, and the magnetic South Pole becoming north. Fortunately, when they say ‘soon’, they are thinking in geological timescales and they actually mean sometime in the next few thousand years.
Fig: A Road Sign at The South Pole.
It’s thought that the Earth’s magnetic field is generated by the molten iron core at the center of the planet. The molten iron has currents of its own, just like an ocean, and these moving currents create the magnetic field. But the currents are not consistent and the Earth’s magnetic field moves around, with the magnetic north pole currently drifting by about 10 miles a year.
Why it changes?
Earth's polarity is not a constant. Unlike a classic bar magnet, or the decorative magnets on your refrigerator, the matter governing Earth's magnetic field moves around. Geophysicists are pretty sure that the reason Earth has a magnetic field is because its solid iron core is surrounded by a fluid ocean of hot, liquid metal. This process can also be modeled with supercomputers. Earth is a dynamic planet, so the flow of liquid iron in Earth's core creates electric currents, which in turn create the magnetic field. So while parts of Earth's outer core are too deep for scientists to measure directly, we can know of movement in the core by observing changes in the magnetic field. The magnetic north pole has been shifting northward – by more than 600 miles (1,100 km) – since the early 19th century, when explorers first located it precisely. It is moving faster now, actually, as scientists estimate the pole is migrating northward about 40 miles per year, as opposed to about 10 miles per year in the early 20th century.
But this movement of the field is small. So what is there to suggest that a flip is imminent? Geophysicists have been studying the lava that has seeped up from the core and through a ridge on the floor of the Atlantic Ocean. As lava cools and solidifies, it preserves the direction of the Earth’s magnetic field so looking at the rock that has formed over time gives us an idea of what has happened to the magnetic poles in the past. These studies show that the poles switch ends every half million years or so – and that we’re due for another switch in the next few thousand years.
There’s also evidence to suggest that before the Earth’s magnetic poles switch, the magnetic field slowly fades out before reappearing with the poles reversed. And our magnetic field has depleted by 5% over the last century.
So do we need to worry?
No, the impending geomagnetic reversal probably won’t cause some kind of apocalypse. Well, birds, sea turtles and bees may get confused as they seem to use the magnetic field to navigate. More drastically, since the Earth’s magnetic field protects us from potentially harmful radiation from the Sun, as it fades we could well be faced with a disaster on a global scale. Fortunately, there’s no evidence in the fossil record of a magnetic field switch causing a species to die out, also we should have plenty of warning (months, years) if that’s the case.