Sunday, April 11, 2004
Timing a Polar reversal
I remember the first time (about 9 years back) I had mentioned the idea of a reversal of the Earth's poles to a friend, he thought I was joking. To this day, I know friends of mine who think it is a joke that the South and North Pole could trade places and that catastrophic results could follow. I digress. Earlier today, I was reading this interesting Discovery story on how a U.S. scientist is now predicting that such a reversal could last all of 7,000 years -- a pretty scary thought if one were to think in terms of the long-drawn out consequences.
The so-called flip between the Earth's North and South poles occurs at long but unpredictable intervals, the most recent one occurring about 790,000 years ago. A compass needle, if one existed then, would have pointed to the south and not to the north. The 180 degree switch occurs when there is a change in the circulation patterns in the molten iron that flows around the Earth's outer core and, like a dynamo, creates the magnetic field. The intensity of the field drops for a while before the circulation rhythm is established and the new polarity occurs.
But scientists have only estimated how long the switching process takes before the new poles become established. Estimates have ranged from a couple of thousand years to 28,000. Clement cast light on this area of uncertainty by analyzing records taken from sedimentary rock samples drilled from various sites around the world. These samples, deposited at four different ages in Earth's history, had a residual magnetic echo from the magnetic field at the time. "These records yield an average estimate of about 7,000 years for the time it takes for the directional change to occur," Clement said.
But the big switchover does not take place in one swoop. It happens more quickly at the equator and takes longer at higher latitudes, the closer you get to the poles. He calculated it took 2,000 years at the equator and about 10,000 closer to the poles. The reason for this, said Clement, is that in the absence of the main north-south magnetic field, the Earth's core develops a weaker secondary field that has many mini-poles at the surface. Eventually the two main poles are established again, but on opposite sides of the planet, and restore their primacy.
Many aspects of life today would be literally turned upside down, both for humans, given our dependence on magnets for navigation, and for migrating animals that use an inner compass. We would also be more exposed to deadly bursts of solar radiation, from which we are normally protected by Earth's magnetic field. And the loss of that shield, would cause solar particles to smash into the upper atmosphere, warming it and potentially causing wrenching climate change. There was a scare in 2002 after French geophysicist Gauthier Hulot discovered a weakening of Earth's magnetic field near the poles, which could be interpreted as an early sign that a flip is near.
The so-called flip between the Earth's North and South poles occurs at long but unpredictable intervals, the most recent one occurring about 790,000 years ago. A compass needle, if one existed then, would have pointed to the south and not to the north. The 180 degree switch occurs when there is a change in the circulation patterns in the molten iron that flows around the Earth's outer core and, like a dynamo, creates the magnetic field. The intensity of the field drops for a while before the circulation rhythm is established and the new polarity occurs.
But scientists have only estimated how long the switching process takes before the new poles become established. Estimates have ranged from a couple of thousand years to 28,000. Clement cast light on this area of uncertainty by analyzing records taken from sedimentary rock samples drilled from various sites around the world. These samples, deposited at four different ages in Earth's history, had a residual magnetic echo from the magnetic field at the time. "These records yield an average estimate of about 7,000 years for the time it takes for the directional change to occur," Clement said.
But the big switchover does not take place in one swoop. It happens more quickly at the equator and takes longer at higher latitudes, the closer you get to the poles. He calculated it took 2,000 years at the equator and about 10,000 closer to the poles. The reason for this, said Clement, is that in the absence of the main north-south magnetic field, the Earth's core develops a weaker secondary field that has many mini-poles at the surface. Eventually the two main poles are established again, but on opposite sides of the planet, and restore their primacy.
Many aspects of life today would be literally turned upside down, both for humans, given our dependence on magnets for navigation, and for migrating animals that use an inner compass. We would also be more exposed to deadly bursts of solar radiation, from which we are normally protected by Earth's magnetic field. And the loss of that shield, would cause solar particles to smash into the upper atmosphere, warming it and potentially causing wrenching climate change. There was a scare in 2002 after French geophysicist Gauthier Hulot discovered a weakening of Earth's magnetic field near the poles, which could be interpreted as an early sign that a flip is near.
