A government minister in the Northern Territory, spruiking a plan to make Darwin “the datacentre capital of the globe,” suggested it might be a good idea to pump out groundwater to keep Earth’s spin steady. If we don’t, she said, we might risk “flipping the poles again.”
Is she right? And what’s she even talking about?
As a palaeomagnetist — someone who studies Earth’s magnetic field and reads ancient rocks to understand how it was in the past — let me walk you through what it means for Earth’s poles to flip, what groundwater has to do with it, and why there is absolutely nothing to worry about.
Which pole, exactly?
The first problem is that there are two very different “north poles.”
The geographic North Pole is the one on every map, and it is the spot where Earth’s spin axis meets the surface. This pole drifts by about 10 cm a year, as ice, water, and movements of Earth’s crust shift mass around the planet.
The magnetic north pole is something else entirely: the spot where the magnetic field points straight down. It slowly wanders around the geographic pole, a restlessness we call secular variation.
The unflippable geographic pole
Can the geographic pole flip? In practice, no.
A spinning Earth behaves like a gyroscope — a spinning top that resists being tipped over. Its axis stays remarkably steady, drifting only very slowly. A sudden flip, with the spin axis tipping right over, is essentially impossible and unknown in Earth’s history.
Scientists once thought evidence of glaciers near the equator, between around 700 million and 635 million years ago, may have been evidence of an ancient drastic move or flip in the geographic pole.
But that explanation has largely fallen away. Most researchers now believe the glaciers occurred during a “Snowball Earth” period, when the world was frozen almost all the way to the tropics.
As for pumping groundwater, it can affect the geographic pole — but only very slightly. From 1993 to 2010, all the groundwater pumped worldwide shifted this pole by about 4 cm a year.
The magnetic pole is a different story
Earth’s magnetic field, by contrast, really does flip. It has happened often in the past, but at irregular and unpredictable intervals.
The last complete reversal was about 780,000 years ago. The most recent big disturbance was the Laschamp excursion roughly 41,000 years ago, when the field’s strength collapsed almost to zero, and the magnetic pole swung down towards the equator before recovering.
Even then, a reversal is no overnight switch: high-resolution sediment records — including from Armenian lake beds — show the field weakening and swinging over thousands of years, with a global average of around 7,000 years. Looking at this restless history, it’s fair to say another reversal is likely at some point in the geological future.
Could it be soon? Some scientists note the field’s strength has been falling steadily and argue a reversal could be only one or two thousand years away. There is currently a weak patch over the South Atlantic known as the South Atlantic Anomaly, which is seen as a possible starting point.
Earth’s magnetic field is generated by swirling liquid iron in the outer core. This system is so complex that no one can truly predict it, and its strength could just as easily start climbing again. And when researchers compared the South Atlantic Anomaly with the Laschamp excursion, they concluded we are probably not on the verge of a reversal at all.
Made deep inside Earth
Crucially, magnetic pole reversals are born in the liquid outer core, between 2,890 km and 5,150 km beneath our feet. We still don’t know exactly why they happen, but we do know that structures deep in the overlying mantle shape how the field behaves during reversals.
These structures affect how often reversals happen and what they look like. The South Atlantic Anomaly itself sits above one such deep structure.
Even the most violent surface events don’t seem to reach that far down. The giant asteroid impact linked to the extinction of the dinosaurs, for example, is not thought to have triggered a reversal.
True polar wander
There is one more kind of pole movement: true polar wander. Here, the spin axis stays fixed in space while the whole solid Earth slowly rotates with respect to it.
This means the poles shift relative to the continents — a gradual drift of up to a few degrees per million years, driven by enormous masses shifting inside the mantle.
In the Precambrian Era, billions of years ago, polar wander probably helped drag Earth’s first supercontinents towards the equator, since a spinning planet is most stable when its biggest masses sit there.
So where does this leave us with groundwater and flipping poles? Earth really is a deeply interconnected system, and moving water around does shift the poles measurably, by centimeters a year.
But a flip of the geographic pole is impossible, and magnetic reversals are almost certainly disconnected from anything we do at the surface. We can nudge the climate, but there is no reason to think we could reach down and flip the switch in Earth’s core.
Uwe Kirscher, Research Fellow, Curtin University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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