The north and south poles have reversed numerous times in Earth’s history. About 800,000 years ago, the last pole reversal took place. This isn’t a fast process either. According to scientists, it can take up to 15,000 years once the reversal begins.
How do African huts factor in? For the first time, researchers have discovered a magnetic field record from ancient materials in southern Africa between 1000 and 1500 AD. Knowledge of ancient African practices was instrumental in gathering the data. Specifically, the ritualistic cleansing of villages in agricultural communities.
During these cleansings, huts and grain bins were burned to the ground. Within these blazes, temperatures were hot enough to erase the magnetic record in a key mineral (magnetite) and create a new magnetic record. This new record included the magnetic field’s strength and direction.
The research team observed a sharp 30 percent decrease in magnetic field intensity from 1225 to 1550 AD.
“It has long been thought reversals start at random locations, but our study suggests this may not be the case,” said John Tarduno, a geophysicist from the University of Rochester.
Today, satellites keep track of the magnetic field intensity with satellites. The intensity in this area is still weakening, but not as quickly. Tarduno and his fellow researchers believe the process behind this weakening may be a repeating feature of the magnetic field.
“Because rock in the deep mantle moves less than a centimeter a year, we know the LLSVP (Large Low Shear Velocity Province) is ancient, meaning it may be a longstanding site for the loss of magnetic field strength,” said Tarduno. “And it is also possible that the region may actually be a trigger for magnetic pole reversals, which might happen if the weak field region becomes very large.”
Tarduno says the new research won’t lead to predictions, but it does suggest today’s pattern could be a recurring feature that can occasionally lead to a global magnetic field reversal.
Since 1840, the Earth’s dipole magnetic field strength has decreased 16 percent. Much of the modern decrease is attributed to the South Atlantic Anomaly. Earth’s inner Van Allen radiation belt dips to an altitude of 200 km in this area (image below). Space agencies keep a close eye on this area as satellites pass through it. For several minutes, satellites are exposed to stronger than usual radiation. The recent weakening in magnetic field strength doesn’t mean a pole reversal is coming. The magnetic field can re-strengthen without a pole reversal.
The study was published in the journal Nature Communications.
What would happen during a pole reversal?
It’s not the actual pole reversal that’s bad. It’s the weak phase before the reversal according to scientists. Tarduno spoke to LiveScience a few years ago and said one of the biggest issues to arise from a weak magnetic field would be coronal mass ejections.
“Some of the particles associated with CMEs can be blocked by Earth’s magnetic field. With a weak field, this shielding is less efficient,” said Tarduno.
Ozone holes could more easily form due to the weaker field. “These ‘holes’ would not be permanent, but might be present on one- to 10-year timescales — arguably important enough to be a concern in terms of skin cancer rates,” said Tarduno.
Technology would also be at risk. The biggest solar storms can already damage satellites and cause power outages. If these storms hit during a time when the magnetic field was at its weakest, the effects would be exacerbated.
But, the odds of any of this happening in our lifetimes is slim.
Image credits: University of Rochester