The Last Magnetic Field Reversal Took Longer Than Previously Thought

Earth’s magnetic field helps protect Earth from the impact of the radiation of the sun, and helps create wonderful hues of light known as the Northern Lights. It helps in navigation and many devices such as compasses work properly thanks to the steady location of the poles. However, although invisibly, the magnetic field drifts and wanes. The North Pole is shifting toward Siberia, which caused the Global Positioning System to define new models to help navigation. Now, a new study found that the last magnetic field reversal on Earth took longer than previously thought, urging scientists to update the navigation software for the expected shift.

Every once in several hundred thousand years Earth’s magnetic field shifts and reverses its polarity. While this reversal has taken place many times throughout Earth’s history, scientists still don’t know what causes it and why it happens.

Research led by Brad Singer, geologist from the University of Wisconsin-Madison studied the last magnetic field reversal that took place 770,000 years ago, finding it took 22,000 years to complete. This took longer than it was previously estimated, given that there are findings suggesting some reversals took place within a human lifespan.

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Scientists conducted new analysis using a global survey of lava flows, ocean sediments and Antarctic ice cores to deliver new results. Over a millennia the magnetic field grew weak, shifted only partially, stabilized again, and then reversed into the orientation that is familiar to us today. Their findings were published in the journal Science Advances in collaboration with Kumamoto University in Japan and the University of California, Santa Cruz.

“Reversals are generated in the deepest parts of the Earth’s interior, but the effects manifest themselves all the way through the Earth and especially at the Earth’s surface and in the atmosphere,” Singer said in a statement. “Unless you have a complete, accurate and high-resolution record of what a field reversal really is like at the surface of the Earth, it’s difficult to even discuss what the mechanics of generating a reversal are.”

Singer and his research team focused on lava flows in Chile, Tahiti, Hawaii, the Caribbean and the Canary Islands. The samples of lava flows contributed to the research in several field seasons.

“Lava flows are ideal recorders of the magnetic field. They have a lot of iron-bearing minerals, and when they cool, they lock in the direction of the field,” said Singer. “But it’s a spotty record. No volcanoes are erupting continuously. So we’re relying on careful field work to identify the right records.”

To date the lava flows, researchers combined magnetic readings and radioisotope dating of the samples they collected. They recreated the model of the magnetic field over the time of 70,000 years, based on the Matuyama-Brunhes reversal. They also measured argon production from radioactive decay of potassium in the rocks using different advanced methods in Singer’s WiscAr lab, finding that the last magnetic field reversal took much longer than previous studies suggested.

Ever since the magnetic field started being recorded, scientists found a decrease in its strength of about 5% each century. Singer’s recordings show that the weakening field may imply an eventual reversal, although scientists don’t have enough information about when it could happen or confirm that it’s inevitable.

A reversing magnetic field may affect navigation and how satellites around Earth work. It could also damage communication systems which depend on it. However, according to the new study, we’ll have enough time to prepare and adapt to some eventual shifting, so there’s no reason to worry.