Earth’s magnetic field long overdue for a reversal that could end our current way of life

survivepoleshift 

Scott Sutherland | Geekquinox

When a reversal does eventually happen, we have a good idea of what it will and won't do — both to us and the planet …The idea that Earth's magnetic field will flip — switching the north and south magnetic poles — isn't anything new. It's even been the topic of choice for some doomsday prophets, since it will, apparently, destroy the planet or at the very least turn it on its side, putting an end to us in either case.

It's well known that the polarity of Earth's magnetic field changes. Geologists have seen this change by examining the floor of the Atlantic Ocean. When magma wells up at the Mid-Atlantic Ridge and is cooled by the ocean water, crystals in the magma will orient themselves in the direction of the Earth's magnetic field. Thus, bands of cooled magma along the ocean floor are a geologic record of what direction the magnetic field pointed in during Earth's history, and show that the magnetic field has reversed every 100,000 to 50 million years or so.

Within the last 5 million years, the reversals have been characterized by long periods of stability, of between 450,000 and 590,000 years, separated by several shorter-term reversals. The last reversal happened around 780,000 years ago, so by reckoning of some, we are long overdue.

Reversals are thought to occur when large areas of the Earth's liquid iron outer core become oppositely-aligned to their surroundings. If enough areas of the outer core do this, the entire magnetic field will flip. This does not happen suddenly, though. It takes thousands to tens of thousands of years for this to occur.

When a reversal does eventually happen, we have a good idea of what it will and won't do — both to us and the planet.

Speculation by some is that when the magnetic field flips, it will be because the solid iron inner core of the planet flips 180 degrees. This will cause the surface of the planet to shift at least 90 degrees, effectively switching our lines of latitude and longitude, and destroying us in the process. However, only the size of the inner core affects the magnetic field, with a growing core making a stronger field and a shrinking core making a weaker field, and a shift in the magnetic field will not effect the orientation of the solid core at all. Even if it did, it would take tens of millions of years for such a change to spread out from the core, through the liquid outer core, and through the mantle, before it reached the Earth's surface and did us in.

What it will do is cause a weak period in the magnetic field strength for a thousand or more years, as the various parts of the liquid outer core sort themselves out to all orient in the same direction. This would expose us to heightened amounts of solar radiation, and solar particles could even punch large, although temporary, holes in the ozone layer. Our technology would bear the greatest brunt of this kind of event, though. Even now, solar storms and coronal mass ejections can cause havoc with computers, communications systems and power grids, and this would be much worse with a weakened magnetic field. Additionally, there would be several magnetic poles during this time, making travel by compass much more difficult. What's certain is that it wouldn't be the end of us, but it would be the end of our current way of life.

There have been some signs that the magnetic field may be on the move, since within the last century, Earth's magnetic field has shifted and has lost some of its strength.

"Magnetic north has migrated more than 1,500 kilometres over the past century," said Conall Mac Niocaill, a geology and geophysics professor at Oxford University. "In the past 150 years, the strength of the magnetic field has lessened by 10 percent, which could indicate a reversal is on the cards."

Or it may not. The field changes, both in direction and strength, are well within the normal range that we've seen over the past million years or so. Also, just because something has happened in the past is no guarantee that it will happen in the future.

On the other hand, a large area underneath South America and the South Atlantic — called the South Atlantic Anomaly — was identified in the 1990s as a weak spot in the Earth's magnetic field, and could indicate a large area of the liquid core changing its polarity. It seems to be the only large area of weakness, though, so who knows if it is simply a temporary phenomenon, or a sign of things to come.

The European Space Agency is launching its 'Swarm' magnetic field mission next month. With two satellites in polar orbit to examine the magnetic field directly, and one satellite in far orbit to examine the effects of solar activity on the field, the mission could bring us much closer to understanding the Earth's magnetic field and gain more insight on how it is changing.