Santa Claus famously lives and works at the North Pole, but which North Pole? There are actually two North Poles of the Earth. One is the Geographic North Pole. This pole is aligned (but not exactly) with the rotational axis of the Earth and is the northernmost place on maps. The second North Pole is the Magnetic North Pole, the location that compasses will point to as north. If Santa wanted to keep his home on the Magnetic North Pole he’d have a hard time of it. Magnetic North is always moving.
The Magnetic North Pole is unstable due to the underlying forces that create it. The metal core of the Earth is the source of its magnetic field. The innermost part of the core is solid and composed mostly of iron. The outer part of the core is hot liquid metal in a state of constant motion. The flow of the outer core creates electric currents, which in turn create a magnetic field.
The flow of the outer core isn’t constant, so the North Magnetic Pole drifts. It has moved north by about 600 miles since it was first located in the 19th century. Slowly, its movement has been increasing. Magnetic north has been moving about 40 miles per year recently. Santa would have to move shop every winter if he wanted to keep his workshop on the Magnetic North Pole!
Sometimes the magnetic poles change even more dramatically. Throughout the history of the earth there have been a series of what are called “geomagnetic reversals.” When a geomagnetic reversal occurs, magnetic north and south trade places. Right now we are in a period of “normal polarity,” where magnetic north is near geographic north. In times of “reverse polarity,” magnetic north is located near geographic south (and a compass would point towards south instead). If Santa was trying to stay on magnetic north during a reversal, he’d have to move to Antarctica!
There have been over 300 geomagnetic reversals over the last three billion years. They happen every 100,000 to 1 million years. You may notice that this is a rather large range. Geomagnetic reversals occur seemingly at random. They aren’t predictable and don’t occur at a steady rate. The most recent full reversal was around 780,000 years ago. How do we know this? The answer is in rocks.
Scientists who first discovered geomagnetic reversals noticed something strange in volcanic rocks. Volcanic rocks have ferromagnetic minerals in them, and some rocks were magnetized opposite to the direction of the current magnetic field. Researchers over the last hundred years have looked at volcanic rocks all over the world to create a timeline of ancient magnetism (called paleomagnetism). Based on the behavior of the current magnetic field, as well as the length of time it’s been since our last reversal, geologists estimate that we’re due for another geomagnetic reversal soon. Should we be worried? Not really.
During a geomagnetic reversal, the magnetic field around the Earth weakens. Early scientists feared that this weakening would leave the Earth vulnerable to solar radiation, but there is no evidence to support this. Even a weakened magnetic field would still have the strength to repel some radiation, and the atmosphere does an excellent job of blocking the rest. There are small increases in solar radiation during a reversal, but not enough to cause serious harm. Paleontologists examining the fossil record have found no disruption in plant and animal life associated with geomagnetic reversals, which further validates these explanations.
At any rate, “soon” is highly relative in geologic terms. It is very likely that a geomagnetic reversal will happen within the next thousand years. While this is “soon” in a geologic time frame, it isn’t likely to affect us, our grandchildren, or even our great-great-grandchildren. Either way, the Earth has survived a multitude of reversals in its history and will undoubtedly survive many more. Santa will just have to keep on his toes if he wants to keep track of the North Magnetic Pole!
- Kate Dzikiewicz, Paul Griswold Howes Fellow