It is fairly common knowledge that, when placed upon a flat surface anywhere in the world, the arms of a magnetic compass will swing round, gently oscillating until they reveal one’s orientation in relation to the North and South Poles. This is possible because of the Earth’s magnetic field which, generated by the movement of iron-rich fluid in its hot, molten outer core, can be described as a simple dipole which means that it has two Poles (located in the planet’s polar regions). A lesser known fact, perhaps, is that, for as long as the record shows, this field has been experiencing periodic reversals in which magnetic North and South switch places completely.
Evidence of these reversals, taken from the Geological record and visible mainly in the iron-bearing minerals found in volcanic rocks, particularly those on the ocean bed, tells us that the magnetic field flips periodically with around 4 to 5 reversals observed every million years over the past 10 million years. This translates roughly to approximately one reversal every 200,000 to 300,000 years. Though this makes them a fairly frequent occurrence (within a geological timescale), simulations suggest that the outer core actually attempts a reversal every few thousand years. The majority of these, however, are thwarted by the less flexible (quite literally) solid, inner core meaning that hundreds of thousands of years pass between each successful reversal. Like many natural processes, the significant aspect of unpredictability means that the lengths of these intervals can vary and, at present, no major change has been recorded in Earth’s polarity for nearly 800,000 years. This would suggest that a reversal is imminent, though there is not enough data to envisage at what rate it will occur with models predicting anywhere between one and several thousand years.
But what will this mean for life on Earth? Given that the earliest measurements of the Earth’s magnetic field only date back to the 16th century, not to mention that the planet has not experienced a reversal for the better part of the last million years, scientists cannot be too certain of exactly how a reversal will manifest itself. However, it is not thought that the consequences of a polar flip will have too devastating an effect. Magnetic field reversals have previously been linked to widespread extinction, though this theory has since been dismissed as the record of reversal does not match up with that of mass extinction events.
A reversal would more likely result in a brief period (geologically speaking) of confusion for animals such as birds, whales and turtles who make use of Earth’s magnetic field for migration purposes, along with some pretty dodgy compass readings. All of which would eventually be resolved using the tried and tested survival technique that is: adaptation – both on our part and the animals’.
Above all, the next reversal will mark the first to occur since the development of modern science, since the existence of humans on the planet, for that matter, and so it will provide an opportunity to study this natural phenomenon, yet to be experienced in human history, and gain a greater understanding of the complex workings of our planet.
By Theodora Lonsdale