Scientists understand that Earth’s magnetic field has flipped its polarity many times over the millennia. In other words, if you were alive about 800,000 years ago, and facing what we call north with a magnetic compass in your hand, the needle would point to ‘south.’ This is because a magnetic compass is calibrated based on Earth’s poles. The N-S markings of a compass would be 180 degrees wrong if the polarity of today’s magnetic field were reversed. Many doomsday theorists have tried to take this natural geological occurrence and suggest it could lead to Earth’s destruction. But would there be any dramatic effects? The answer, from the geologic and fossil records we have from hundreds of past magnetic polarity reversals, seems to be ‘no.’
Reversals are the rule, not the exception. Earth has settled in the last 20 million years into a pattern of a pole reversal about every 200,000 to 300,000 years, although it has been more than twice that long since the last reversal. A reversal happens over hundreds or thousands of years, and it is not exactly a clean back flip. Magnetic fields morph and push and pull at one another, with multiple poles emerging at odd latitudes throughout the process. Scientists estimate reversals have happened at least hundreds of times over the past three billion years. And while reversals have happened more frequently in “recent” years, when dinosaurs walked Earth a reversal was more likely to happen only about every one million years.
Sediment cores taken from deep ocean floors can tell scientists about magnetic polarity shifts, providing a direct link between magnetic field activity and the fossil record. The Earth’s magnetic field determines the magnetization of lava as it is laid down on the ocean floor on either side of the Mid-Atlantic Rift where the North American and European continental plates are spreading apart. As the lava solidifies, it creates a record of the orientation of past magnetic fields much like a tape recorder records sound. The last time that Earth’s poles flipped in a major reversal was about 780,000 years ago, in what scientists call the Brunhes-Matuyama reversal. The fossil record shows no drastic changes in plant or animal life. Deep ocean sediment cores from this period also indicate no changes in glacial activity, based on the amount of oxygen isotopes in the cores. This is also proof that a polarity reversal would not affect the rotation axis of Earth, as the planet’s rotation axis tilt has a significant effect on climate and glaciation and any change would be evident in the glacial record.
Earth’s polarity is not a constant. Unlike a classic bar magnet, or the decorative magnets on your refrigerator, the matter governing Earth’s magnetic field moves around. Geophysicists are pretty sure that the reason Earth has a magnetic field is because its solid iron core is surrounded by a fluid ocean of hot, liquid metal. This process can also be modeled with supercomputers. Ours is, without hyperbole, a dynamic planet. The flow of liquid iron in Earth’s core creates electric currents, which in turn create the magnetic field. So while parts of Earth’s outer core are too deep for scientists to measure directly, we can infer movement in the core by observing changes in the magnetic field. The magnetic north pole has been creeping northward – by more than 600 miles (1,100 km) – since the early 19th century, when explorers first located it precisely. It is moving faster now, actually, as scientists estimate the pole is migrating northward about 40 miles per year, as opposed to about 10 miles per year in the early 20th century.
Another doomsday hypothesis about a geomagnetic flip plays up fears about incoming solar activity. This suggestion mistakenly assumes that a pole reversal would momentarily leave Earth without the magnetic field that protects us from solar flares and coronal mass ejections from the sun. But, while Earth’s magnetic field can indeed weaken and strengthen over time, there is no indication that it has ever disappeared completely. A weaker field would certainly lead to a small increase in solar radiation on Earth – as well as a beautiful display of aurora at lower latitudes – but nothing deadly. Moreover, even with a weakened magnetic field, Earth’s thick atmosphere also offers protection against the sun’s incoming particles.
The science shows that magnetic pole reversal is – in terms of geologic time scales – a common occurrence that happens gradually over millennia. While the conditions that cause polarity reversals are not entirely predictable – the north pole’s movement could subtly change direction, for instance – there is nothing in the millions of years of geologic record to suggest that any of the 2012 doomsday scenarios connected to a pole reversal should be taken seriously.
There’s a renewed interest right now in Earth’s magnetic poles – specifically, whether or not they’re about to flip, and what may happen. The consequences of this seemingly rapid geomagnetic backflip may sound a little ominous, but don’t worry: we’re not sure when the next reversal will happen, and even when it does, the risks aren’t likely to be as scary as you may think.
Let’s start with the basics.
As Earth’s liquid, iron-rich outer core gradually cools, it sloshes around through colossal convection currents, which are also somewhat warped by Earth’s own rotation. Thanks to a quirk of physics known as the dynamo theory, this generates a powerful magnetic field, with a north and south end.
Although 99 percent of the magnetic energy remains within the core, the slithers that escape extend into space, and spends most of its time deflecting potentially deadly, atmosphere-stripping solar wind.
Right now, the magnetic north pole is exactly where you suspect it is; the same goes for the magnetic south pole. Both represent locales in which the planet’s magnetic field is vertical, and at which point your compass needle tries to point upwards.
Throughout geological time, these magnetic poles have switched sides – a phenomenon known as a “geomagnetic reversal”. Although there are several hypotheses that attempt to explain this, geophysicists are still a little unsure as to why it happens. It’s clearly something to do with turbulence and chaos within the metallic outer core, but the specifics haven’t been nailed down yet.
This is bad news for anyone who enjoys life without radiation sickness.
The Earth’s magnetic field is a barrier which shields us from a lot of harmful solar radiation, attracting cosmic rays towards our planet’s poles so that they shoot harmlessly past us without doing too much damage. If the field were to become weak enough during this transitional period, more radiation would bake the planet than we’re typically used to, which could ultimately render large parts of the Earth uninhabitable for a long time to come.
What’s more, our technology won’t fare too well once the magnetic field begins to weaken—orbital satellites in particular will suffer from solar buffeting without the convenient protection that’s currently provided by the Earth’s magnetic field. Down on the planet itself, things could get hectic too—solar flares would do more damage than normal, overloading power grids, causing computers to fail, and generally running amok.
This wouldn’t be a small global problem that would pass harmlessly afterwards. Because it takes hundreds of years for the planet’s poles to stabilize, entire generations of humans would be constantly affected, unable to use the technology that has become, and will continue to become, such a large part of our lives.
The greatest threat that this poses to humans is via the sun. With a weak magnetic field, we would be far more exposed to CMEs (Coronal Mass ejections), in which flaming hot materials from the Sun are thrown into space at high speeds (around 5,000,000mph), often in the direction of Earth. These would easily create temporary punctures in our ozone layer, causing massive exposure to UV rays. Some scientists predict that skin cancer rates would skyrocket.
Or, nothing happens…