According to scientists, the Earth’s magnetic field is moving towards a reversal – a geological phenomenon which, while it may sound cataclysmic, has happened many times before. In fact, Earth’s geologic record shows that hundreds of pole reversals have taken place throughout the planet’s history.
Although complete reversals have been somewhat irregular, scientists believe they have happened every 200,000 to 300,000 years. That is, except the most recent one, which occurred 780,000 years ago, during the Stone Age. The evidence that exists today suggests that Earth might now be in the early stages of a pole reversal. It is not, however, anything we will experience in our lifetimes or even which our greatgrandchildren may experience, as it is an incredibly slow process, taking between 1,000 and 10,000 years to complete.
According to scientists, the strength of Earth’s magnetic field has been decreasing at what they call an “alarming rate” for at least the last 160 years – hence their theory that we are currently heading towards a reversal. Satellite data gathered by the European Space Agency (ESA) shows that Earth’s magnetic shield is weakening 10 times faster than previously thought, at 5 % per decade. This is happening primarily over South America, in an area which scientists have dubbed the South Atlantic Anomaly (SAA), and which stretches across the Atlantic Ocean from Chile to South Africa. Since this region was first discovered in 1958, its girth has been steadily increasing, part of an overall weakening of the entire magnetic field. Indeed, satellites flying over this area frequently have their circuits fried by localised radiation spikes.
A weakening magnetic field does not have to mean the poles are about to reverse. Sometimes, the field recovers its original structure, a waning-recovering event known as a geomagnetic excursion. Researchers from the Universities of Liverpool and Iceland, and the GFZ German Research Centre for Geosciences, have been looking into this and studying past excursions. They argue that there are two periods in history – 49,000 and 46,000 years ago respectively – where anomalies like the SAA (but stronger) occurred, neither of which caused a pole reversal.
The Earth’s core is made up of molten iron which, as it flows, produces an electrical current, which in turn creates the Earth’s magnetic field. It is by way of this magnetic field that we can navigate. When a compass needle points north, it is in fact pointing to Earth’s magnetic south. This is because magnetic opposites attract. Scientists’ explanation of exactly how the pole reversal happens is simple enough: Patches of iron atoms in Earth’s liquid outer core become reverse-aligned, like little magnets oriented in the opposite direction to those around them. When these reversed patches increase in size to the extent that they dominate the rest of the core, the overall magnetic field flips.
The Earth’s last complete pole reversal was named the Brunhes-matuyama reversal, and it happened at a time when plant and animal life on the planet was flourishing. Fossils dating to this period have led geophysicists to believe that the poles switching had no catastrophic impact on life. This belief is supported by glacial records, which indicate that the reversal did not cause a rotation or shift in the Earth’s axis – an occurrence which would have drastically altered the planet’s climate.
While the effects of the aforementioned polar flip seem to have been minimal, scientists cannot say for certain what a pole reversal would mean today. What they are sure of is that, while Earth’s magnetic field will not disappear entirely, it could weaken drastically. This would alter the functionality of technological devices, satellites and power grids, and give those in the aviation industry some serious new challenges. Another cause for concern could be the effect on Earth’s fauna. Many animal species have magneto reception, which they use to navigate, such as when they migrate. A weakened field would disorient those species which rely on geomagnetism for navigation, such as bees, pigeons, salmon, turtles, whales, and even certain bacteria.
Where a polar reversal will probably have the greatest impact, scientists say, concerns radiation. This is because a strong magnetic field works to protect Earth from the sun’s radiation blasts, and thus a weakened magnetic field could lead to the formation of “ozone holes”. Officials at NASA predict that the resultant increase in solar radiation would be small, and luckily not deadly.
As to whether a flip will cause a shift in the continents, or natural disasters like earthquakes, scientists say that it’s not likely. Changes in the Earth’s liquid core happen on a different distance and timescale to convection in the planet’s mantle – the process that causes Earth’s tectonic plates to shift. While the liquid core does come into contact with the bottom of the mantle, scientists say it would take tens of millions of years for changes in the core to work their way through the mantle and influence the motion of the tectonic plates.
Ultimately, Earth is too complex a system for scientists to know with certainty which outcome to expect – a reversal or a geomagnetic excursion. If the reversal should happen, at least Earth’s inhabitants will have plenty of time – a few thousand years, in fact – to adjust to the changes.