A recent study published in the journal Earth and Planetary Science Letters shows that such a reversal may happen more frequently than scientists previously thought.
According to the team of French and Russian scientists, this is was likely the case during the Cambrian period 500 million years ago, when the Earth’s early life forms were undergoing evolutionary growth spurts.
To calculate how frequent field flips were during the period, the researchers looked at the orientation of magnetic particles trapped in Cambrian sediments. The orientation of the particles corresponded to the direction of Earth’s magnetic field at the time and place the sediment was deposited. The researchers then verified the age of the sediments by dating trilobite fossils found in the same layer.
They found that around 500 million years ago, the magnetic field flipped about 26 times every million years or so – extreme by most standards. Lead author Yves Gallet, the research director of the French National Center for Scientific Research at the Institute of Physics of the Globe of Paris, said that five flips per million years were already considered very high.
What’s more, Gallet said that field reversal frequency plummeted extremely quickly shortly after this period. Between 495 million and 500 million years ago, the magnetic field started flipping around one to two times every million years.
While most scientists agree that field reversal frequency will only evolve gradually across tens of millions of years, Gallet’s team found “a sudden change in reversal frequency occurring on a million-year timescale.” He did clarify that the conditions driving the magnetic field in the outer core 500 million years ago were drastically different from those occurring today. It’s still a mystery, however, what those conditions were. Figuring those conditions out could help explain why Earth flipped so frequently during that seemingly anomalous period.
One explanation is that temperatures dropped at the boundary between the liquid-iron outer core and the mantle. In fact, previous research suggested that the inner core likely cooled and solidified around 600 or 700 million years ago, so it’s possible this had a significant impact on the magnetic field, said Gallet.
There has been some talk among experts that a field reversal may be imminent. This is based on the fact that an unusually weak region in Earth’s magnetic field, the South Atlantic Anomaly, has been growing as of late.
The spot, located several miles off the coast of Brazil and extending over much of South America, causes cosmic particles to dip closer into the atmosphere. In addition, this anomaly appears to be in the process of splitting into two lobes, according to National Aeronautics and Space Administration scientists.
To be sure, a field switch is not going to be catastrophic if it does happen. But it will knock out more satellites and navigation tools and permit more radiation that can trigger a sharp uptick in skin cancer cases. (Related: If the Earth’s magnetic field reverses, scientists think they know where ground zero will be.)
Still, such a reversal is likely to happen anytime soon, at least not in this lifetime. According to Gallet, “It is important to remember that the timescale we are considering for the evolution in magnetic reversal frequency is at least a few millions of years.”
For that reason, “a magnetic polarity reversal is not for tomorrow,” he said.
Physics.news has more on the likelihood of a magnetic field reversal.