The end of the world as we know it could come in any number of ways, depending on who you ask. Some people believe global cataclysm will occur when Earth's magnetic poles reverse. When north goes south, they say, the continents will lurch in one direction or the other, triggering massive earthquakes, rapid climate change and species extinctions.

The geologic record shows that hundreds of pole reversals have occurred throughout Earth's history; they happen when patches of iron atoms in Earth's liquid outer core become reverse-aligned, like tiny magnets oriented in the opposite direction from those around them. When the reversed patches grow to the point that they dominate the rest of the core, Earth's overall magnetic field flips. The last reversal happened 780,000 years ago during the Stone Age, and indeed there's evidence to suggest the planet may be in the early stages of a pole reversal right now.

But should we really fear this event? What will actually happen when north-pointing compasses make a 180-degree turn toward Antarctica? Will the continents tear themselves apart, or are we in store for much more mundane changes?

Weak field

"The most dramatic changes that occur when the poles reverse is a very large decrease of the total field intensity," said Jean-Pierre Valet, who conducts research on geomagnetic reversals at the Institute of Earth Physics of Paris. [5 Ways the World Will Change Dramatically this Century]

Earth's magnetic field takes between 1,000 and 10,000 years to reverse, and in the process, it greatly diminishes before it re-aligns. "It's not a sudden flip, but a slow process, during which the field strength becomes weak, very probably the field becomes more complex and might show more than two poles for a while, and then builds up in strength and [aligns] in the opposite direction," said Monika Korte, the scientific director of the Niemegk Geomagnetic Observatory at GFZ Potsdam in Germany.

Supercomputer models of Earth's magnetic field. On the left is a normal dipolar magnetic field. On the right is the sort of complicated magnetic field Earth has leading up to a reversal. (Image credit: NASA)

The scientists say it's the weak in-between phase that would be roughest on Earthlings.

According to John Tarduno, professor of geophysics at the University of Rochester, a strong magnetic field helps protect Earth from blasts of radiation from the sun. "Coronal mass ejections (CMEs) occasionally occur on the Sun, and sometimes hurtle directly toward Earth," Tarduno said. "Some of the particles associated with CMEs can be blocked by Earth's magnetic field. With a weak field, this shielding is less efficient."

The charged particles bombarding Earth's atmosphere during solar storms would punch holes in Earth's atmosphere, and this could hurt humans. "Ozone holes, like that over Antarctica (which today are due to an entirely different cause related to man) could form as solar particles interact with the atmosphere in a cascade of chemical reactions. 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," Tarduno said. [Will Sunscreen Protect You from the Upcoming Solar Flares?]

Valet agrees that a weak magnetic field could lead to the formation of ozone holes. He wrote a paper last year proposing a direct link between the demise of Neanderthals, our evolutionary cousins, and a significant decrease of the geomagnetic field intensity that occurred exactly at the same period. (That time, the lead-up to a geomagnetic reversal appears to have been "aborted"; the field weakened but didn't end up flipping.)

Other scientists aren't convinced that there's a connection between pole reversals and species extinctions. "Even if the field becomes very weak, at the Earth's surface we are shielded from radiation by the atmosphere. Similarly as we cannot see or feel the presence of the geomagnetic field now, we most likely would not notice any significant change from a reversal," Korte said.

Our technology definitely would be in danger, however. Even now, solar storms can damage satellites, cause power outages and interrupt radio communications. "These kinds of negative influences clearly will increase if the magnetic field and thus its shielding function became significantly weaker, e.g. during a reversal, and it will be important to find mitigation strategies," she told Life's Little Mysteries.

One additional worry is that a weakening and eventual reversal in the field would disorient all those species that rely on geomagnetism for navigation, including bees, salmon, turtles, whales, bacteria and pigeons. There is no scientific consensus on how those creatures would cope.

Continental shifts?

Many of the disaster scenarios associated with geomagnetic pole reversals in popular imagination are pure fantasy, the scientists said. There definitely won't be any break-up or shift of the continents.

The first proof is the geologic record. When the last pole switch happened, "no worldwide shifting of continents or other planet-wide disasters occurred, as geoscientists can testify to from fossil and other records," said Alan Thompson, head of geomagnetism at the British Geological Survey.

The scientists explained that changes in the Earth's liquid core happen on a completely different distance and timescale than convection in the Earth's mantle (which causes Earth's tectonic plates to shift, moving the continents). The liquid core does indeed touch the bottom of the mantle, but it would take tens of millions of years for changes in the core to propagate up through the mantle and influence the motion of the tectonic plates. In short, "there is no evidence from the geological past and in my opinion also no conceivable method that magnetic reversals couldtrigger Earthquakes," Korte said.

Sooner or later

The geomagnetic field is currently weakening, possibly because of a growing patch of reverse-alignment in the liquid core deep beneath Brazil and the South Atlantic. According to Tarduno, the strength of Earth's magnetic field "has been decreasing for at least 160 years at an alarming rate, leading some to speculate that we are heading toward a reversal."

Image of the South Atlantic Anomaly (SAA), the region where Earth's magnetic field is weakest, taken by the ROSAT satellite in the 1990s. (Image credit: NASA)

The reversal might happen, or it might be aborted — Earth is too complex a system for scientists to know which outcome to expect. Either way, the process will drag on over the next few thousand years, giving us time to adjust to the changes.

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