The Earth's magnetic field is crucial for life on Earth. Generated by the molten iron core 3000 km beneath our planet's surface, it keeps us enclosed in an electromagnetic blanket that protects both the atmosphere and satellites from excessive solar radiation. This field, however, is continually changing both in strength and direction. How quickly this happens has long been a topic of debate, and now we may closer to knowing the answer.
Historically, the fastest changes in the Earth's magnetic fields have been reversals- when the north pole becomes the south pole and vice versa. These seem to occur at regular intervals a few times every million years. But scientists have now identified field changes that occured faster and more recently than previously recorded polarity reversals- the last of which was 800,000 years ago.
In a new study, researchers combined computer models based on the physics of field generation with a recently published reconstruction of global variations in the Earth's magnetic field for the last 100,000 years.
All in all, the model showed that the Earth's magnetic field changed up to ten degrees per year- ten times more than the previously fasted-reported variations from analyzing sediment records from central Italy.
The researchers also found that the fastest changes in the geomagnetic field direction seem to have happened 39,000 years ago. This shift came after the global 'Laschamp excursion', a 'failed reversal' of the Earth's magnetic field around 41,000 years ago in which the Earth's poles briefly moved far from the geographic poles before swiftly returning.
Lastly, they found that the fastest changes in magnetic polarity tended to be caused by the movement of magnetic field patches across the liquid core's surface. As these patches are mostly found at lower altitudes, the researchers suggest others to focus on these areas to observe other rapid magnetic changes in the future.
While shifts in the Earth's magnetic field do not necessarily pose a direct threat to life on Earth, they may threaten our electromagnetic infrastructure. Space events such as geomagnetic storms could, for example, disrupt satellite communications, GPS, and power grids, and thus majorly disrupt economies. One estimation says that a space weather event could damage the US power grid to a tune of $1 trillion. As such, space weather is considered a 'high priority risk' by the UK national risk register.
Sources: The Conversation, Nature