Livermore and Mound report what most of you readers know that the Earth magnetic field surrounds our planet like an invisible force field, protecting life from harmful solar radiation by deflecting charged particles away. Far from being constant, this field is continuously changing. Indeed, our planetary history includes at least several hundred global magnetic reversals, where north and south magnetic poles swap places. So when is the next one happening and how will it affect life on Earth?
During a reversal the magnetic field will not be zero, but will assume a weaker and more complex form. It may fall to 10% of the present-day strength and have magnetic poles at the equator or even the simultaneous existence of multiple north and south magnetic poles.
Geomagnetic reversals occur a few times every million years on average. However, the interval between reversals is very irregular and can range up to tens of millions of years. There can also be temporary and incomplete reversals, known as events and excursions, in which the magnetic poles move away from the geographic poles perhaps even crossing the equator before returning back to their original locations. The last full reversal, the Brunhes-Matuyama, occurred around 780,000 years ago. A temporary reversal, the Laschamp event, occurred around 41,000 years ago. It lasted less than 1,000 years with the actual change of polarity lasting around 250 years.
The alteration in the magnetic field during a reversal will weaken its shielding effect, allowing heightened levels of radiation on and above the Earth surface. Were this to happen today, the increase in charged particles reaching the Earth would result in increased risks for satellites, aviation, and ground-based electrical infrastructure. Geomagnetic storms, driven by the interaction of anomalously large eruptions of solar energy with our magnetic field, gives a foretaste of what we can expect with a weakened magnetic shield. See SpaceWeather.com
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