Earth’s magnetic field is generated by an interaction between rotation in the planet’s core and electrical currents. The field then creates the magnetosphere, which acts sort of like a force field, protecting the planet from the brunt of the sun's solar wind. This field has both a North and South pole, which can be used for navigational purposes, and they are not static. Variations in the electric current have caused the poles to migrate as much as 16 km (10 miles) per year.
The field itself is not fixed either, and about every 450,000 years or so, the poles actually reverse. This puts the magnetic North where the South was, and vice versa. Last month, a team from the University of California, Santa Cruz was able to determine that the last pole reversal occurred roughly 786,000 years ago over the course of less than 100 years -- within a single human lifetime. Typically, these events take place over the course of thousands of years.
The planet seems to be long overdue for a field reversal: there is evidence that these events happen more frequently than they used to hundreds of millions of years ago. This could be due to the inner core growing larger, which is obstructing the outer core, resulting in a magnetic field that isn’t quite as solid.
Evidence of magnetic field reversals can be seen in rocks. When molten rock cools, the metal components are oriented toward the field. By looking at layers of rock, geologists are able to observe where the metallic molecules are pointing, and thus, determine the direction of the magnetic field.
The European Space Agency’s Swarm constellation uses three satellites to study the Earth’s magnetic field as well as the oceans and the planet’s inner structure. At a Swarm science meeting held in Copenhagen this past summer, it was announced that the magnetic field has been weakening by roughly 5% every 10 years. A weakening or unstable magnetic field could be a sign that a reversal is about to occur. The strength of the magnetic field normally does fluctuate a little bit, but the rate that this appears to be happening is larger than normal. The field appears to be weakening about ten times faster than previously predicted, indicating that an event could be coming sooner rather than later.
If the poles flip, having a compass that points South instead of North doesn’t seem like too big of a deal to humans, but there is a question of what will happen other animals. Certain migratory animals like sea turtles and birds use the magnetic field in order to orient themselves. A reversal of the poles could interfere with their ability to do so.
Another concern about the reversal is that the weakening of the magnetic field which precedes the flipping event will mean that it will not be able to adequately shield us from the sun’s radiation. Though there is no evidence in the fossil record of a mass extinction correlating with a field reversal or an influx of radiation, this could potentially be problematic to power grids and satellites.
[Hat tip: BBC Earth]