500 years before the middle of a magnetic dipole reversal
at the middle of the reversal
500 years after the middle of the reversal
Our planet’s magnetic field reverses about once every 200,000 years on average. However, the time between reversals is highly variable. The last time Earth’s magnetic field flipped was 780,000 years ago, according to the geologic record of Earth’s polarity.
Peter Olson, a geophysicist at Johns Hopkins University in Baltimore, Maryland, said scientists can now pinpoint the core-mantle boundary where these instabilities in the magnetic field are happening.
One such disturbance Olson has been observing recently formed over the east-central Atlantic Ocean. Like a little hurricane, the anomaly swept toward the Caribbean and is moving up in the direction of North America.
“It’s a new one, a little thing,” Olson said. “Time will tell whether it develops into something significant. But it is here in the North Atlantic, moving towards the Pentagon. We can track it over the next couple of decades.”
Instabilities such as this, Olson added, are causing Earth’s magnetic field to weaken. Today the field is about 10 percent weaker than it was when German mathematician Carl Friedrich Gauss first began measuring it in 1845. Some scientists speculate the field is headed for a reversal.
Most of us like stability in our lives, especially when it comes to planet-wide phenomena, such as the daily appearance of the sun or the periodic change of season. So it can be unsettling to learn of global phenomena that are inherently unstable, unpredictable. Such is the case with the Earth’s magnetic field. Every so often, our planet’s magnetic poles reverse polarity (see When Compasses Point South).
Compass needles have always pointed north; in a reversal, they would point south.
You could perhaps take comfort in the knowledge that these reversals happen infrequently—on average every 250,000 years—but maybe not when you consider that it’s been over 700,000 years since the last reversal, and the next one may be currently underway.
Current evidence suggests we are now approaching one of these transitional states because the main magnetic field is relatively weak and rapidly decreasing, he says. While the last polarity reversal occurred several hundred thousand years ago, the next might come within only a few thousand years.
“Right now, historic records show that the strength of the magnetic field is declining very rapidly. From a quick back-of-the-envelope prediction, in 1,500 years the field will be as weak as it’s ever been and we could go into a state of polarity reversal,” says Singer. “One broad goal of our research is to provide some predictive capability for what could happen and what could be the signs of the next reversal.”
Global light show
So is the Earth about to flip? The safe bet may disappoint screenplay writers everywhere.
“Chances are we’re not,” said Dr Bloxham. “Reversals are rare events.”
And they would certainly not threaten life on Earth as they do in science fiction. Although there would be extra radiation exposure to satellites and some airplanes, there would also be enough of a residual field to provide protection to people, and certainly no more radiation than what is observed at the poles, where the field lines currently dip.
But there would be some bizarre readjustment. Prior to Earth’s poles re-establishing themselves, a period of disorder would produce multiple poles, according to Dr Bloxham, which may make backwoods camping tricky.
“Getting around using a magnetic compass would be a more complicated endeavour,” he said.
A collapse would also produce a great increase in auroral activity – the beautiful display of lights generated by solar particles that follow the magnetic field lines down into the atmosphere.
And there would be plenty to time to grab a camera – the reversal is gradual.
This would give animals which use the magnetic field for navigation, such as some birds, turtles and bees, time to reorient themselves.
“They’d go through many generations in the period in which the field was entering the phase of reversal,” said Dr Bloxham. “Presumably they would learn new behaviour patterns to accommodate it.”
Really cool query page:
NASA researchers have found out what sequence of events creates the Northern Lights.
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