|The Earth’s magnetosphere and the Sun. Illustration: NASA|
A new study analyzing rock formations from 107,000 to 91,000 years ago has revealed something troubling: a strangely quick reversal of the Earth’s magnetic field in fairly recent history.
A large team of researchers from China, Taiwan and Australia has found evidence of faster-than-expected shifts in Earth's magnetic polarity several thousand years ago. In their paper published in Proceedings of the National Academy of Sciences, the group describes their study of stalagmites found in a cave in China and what they found.
Prior research has shown that the Earth's magnetic field sometimes reverses polarity—such an event has been experienced only once by modern humans, but that was long before the age of satellites and electronics.
In the modern age, such a reversal could spell trouble for many devices that we have come to rely on. For that reason, scientists study past reversals in the hope of predicting when the next might occur.
The Earth's magnetic field is generated by liquid metal churning at depths 1,700 miles below the surface. But sometimes, that churning can change slightly, affecting the magnetic field. Prior research has suggested that a full reversal would likely take thousands of years, but this new research suggests it can happen in as few as 100.
The researchers report that the stalagmite sample taken from the cave showed evidence of magnetic field changes from 107,000 to 91,000 years ago—a span of 16,000 years. By studying the sample very precisely using a high-resolution cryogenic magnetometer, the researchers were able to trace changes in the magnetic field more precisely than has ever been done before.
In so doing, they discovered that approximately 98,000 years ago, a magnetic reversal occurred over just a century and a half, approximately 10 times faster than had been believed possible. The researchers found several other phase changes, as well, with various degrees of fluctuation strength.
They also found that when the magnetic field was weaker than normal, more fluctuations in strength occurred. They suggest such fluctuations likely caused some instability in convection in the planet's outer core.
The study was published in the journal Proceedings of the National Academy of Sciences.