Earth’s magnetic field is surrounding our planet like a force field invisible to us – protecting living organisms from harmful solar radiation by repelling charged particles away from Earth and this field is constantly changing. Certainly, our planet’s history includes more than several hundred global magnetic reversals, where north and south magnetic poles switch places. So when’s the next one going to happen and in what way will it affect life on Earth? At the time of a reversal, the magnetic field will not be zero but will adopt a weaker and more complex state. It may decrease to 10% of the present-day strength and have magnetic poles at the equator or even the coinciding existence of multiple 'north' and 'south' magnetic poles.
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Geomagnetic reversals occur only a few times about every million years on average. Though, the break between reversals is very irregular and can range up to tens of millions of years. There can also be momentary and incomplete reversals, known as events and excursions, in which the magnetic poles move slightly away from the geographic poles - maybe even crossing the equator - before returning to their original locations. The recent full reversal, the Brunhes-Matuyama, occurred about 780,000 years ago. A temporary reversal, the Laschamp event, occurred about 41,000 years ago. It continued for less than 1,000 years with the real change of polarity lasting around 250 years. Power cut or mass extinction? The change in the magnetic field during a reversal will cause its shielding effect to be weakened, letting sensitive levels of radiation on and over Earth’s surface.
If it is to happen today, the rise in charged particles approaching the Earth would cause in increased risks for satellites, aviation, and ground-based electrical infrastructure. Geomagnetic storms, driven by the anomalously large eruptions of solar energy with the magnetic field of the Earth, give us a sample of what we can expect with a weakening of magnetic shield. In 2003, the so-called Halloween stormcaused the native electricity-grid shutdown in Sweden, required the redirecting of flights to avoid communication shutdown and radiation risk, and disturbed satellites and communication systems. But this storm was nothing in comparison with other storms of the recently in the past, such as the 1859 Carrington event, which caused aurorae as far south as the Caribbean. The effect of a major storm on today’s electronic infrastructure is not entirely known.
Of course, any time spent without electricity, heating, air conditioning, GPS or the internet would have a major effect; widespread shutdowns could result in economic disturbance measuring in tens of billions of US dollars daily. In terms of life on Earth and the direct effect of a reversal on our human beings, we cannot conclusively guess what will happen as modern humans were not present at the time of the last full reversal. Numerous studies have tried to relate past reversalswithmass exterminations - proposing some reversals and episodes of prolonged volcanism could be driven by a common cause.
However, there is no evidence of any forthcoming catastrophic volcanism and so we would only likely have to cope with the electromagnetic impact if the field does reverse comparatively soon. We know that many animal species have some form of magneto-reception that allows them to detect Earth’s magnetic field. They may use this to promotion in long-distance navigation in time of migration. But it is not clear what effect a reversal might have on these species. What is clear is that early humans did survive the Ascham event and life itself has survived the hundreds of full reversals proved in the geologic record.
Can we predict geomagnetic reversals? The simple fact that we are 'overdue' for a full reversal and the fact that Earth’s field at the moment is decreasing at a rate of 5 % per century, has led to propositions that the field might reverse within the next 2,000 years. But pinning down an exact date at least will be very difficult. Earth’s magnetic field is generated within the liquid core of the planet, by the slow churning of molten iron. Just like the atmosphere and oceans, the way in which it moves is directed by the laws of physics. Therefore, we should be able to predict the 'weather of the core' by tracing this movement, just like we can predict the actual weather by looking at the atmosphere and ocean.
A reversal can then be related to a specific type of storm in the core, where the dynamics - and magnetic field - go haywire (at least for a little while), before settling things again. The difficulties of predicting the weather beyond a few days are commonly known, despite us living within and directly observing the atmosphere on a daily basis yet predicting Earth’s core is a far more complex prospect, basically, because it is buried beneath 3,000 km of rock such that our explanations are scarce and indirect. However, we are not entirely blind: we are aware of the major composition of the material inside the core and that it is liquid.
A global network of ground-based observatories and orbiting satellites also calculates how the magnetic field is shifting, which gives us ideas about how the liquid core is moving. The recent discovery of a jet-stream within the core focuses on our evolving creativity and increasing the ability to measure and summarize the dynamics of the core. Combined with numerical simulations and laboratory experiments to study the fluid dynamics of the planet’s core, our understandings are developing sharply. The idea of being able to forecast Earth’s interior is possibly not too far out of reach.
