Earth flips its polarity after every 200,000 to 300,000 yearsPublished On: Thu, Dec 1st, 2011 | Geology | By BioNews
Magnetic pole reversal is a common phenomenon, which occurs on Earth, gradually over the millennia.
According to the scientists, 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.
The science shows that 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.