Earth’s Magnetic Field Flips Regularly — Some Reversals Last 70,000 Years

For at least 4 billion years, an invisible force field has enveloped our planet, protecting us from powerful cosmic radiation. However, the Earth’s magnetic field – essentially a gigantic dipole magnet – is in a state of constant flux and regularly reverses its polarity. In fact, the next reversal might be long overdue, as these reversals typically occur every few hundred thousand years.

Researchers previously thought the reversal process lasted about 10,000 years (the blink of an eye in geological terms) and was accompanied by a weaker shield against radiation that could affect the environment.

Now, researchers from Japan, France and the United States have discovered that some magnetic field reversals last much longer. A study published in Nature Communications Earth and Environment described deep-sea sediment cores revealing that it took about 70,000 years for a magnetic field reversal to occur 40 million years ago. Paleomagnetists say these discoveries expand our understanding of geomagnetic phenomena essential for protecting Earth from solar radiation and other harmful particles from space.

Learn more: What is the Sun’s magnetic field and why is it important?

When magnetic fields reverse

The generator behind Earth’s magnetic field is the outer core of liquid nickel-iron, located about 1,800 miles below the surface, where electric currents create the field. Sometimes the Earth’s poles change polarity (currently the geographic North Pole is a magnetic south pole and the geographic South Pole is a magnetic north pole) in a process known as geomagnetic reversal that lasts for several thousand years.

During this time, the magnetic field destabilizes, reducing the strength of the geomagnetic shield. This weakening can influence atmospheric chemistry, climate and even the evolution of organisms.

“The amazing thing about the magnetic field is that it provides a safety net against radiation from space, and radiation is observed and thought to have all kinds of effects,” Peter Lippert, an associate professor in the University of Utah’s department of geology and geophysics, said in a press release.

He further explained that “it is logical to expect that there will be higher rates of genetic mutations.” [and] atmospheric erosion” and that “this will alter the ability of organisms to navigate” during prolonged exposure to cosmic radiation.

Scientists have observed approximately 540 polarity reversals over the past 170 million years. While most were thought to last around 10,000 years, new analyzes of sediment cores from the North Atlantic suggest that some transitions were much longer.

Sediment cores preserve millions of years of magnetic history

Ancient microorganisms preserved in sediments record Earth’s magnetic past. Some bacteria create internal compasses using environmental iron, producing magnetite crystals that align with the magnetic field. The direction these crystals point in the extracted samples tells scientists the polarity of the planet at that time.

Researchers collected the sediment cores in 2012 from nearly 1,000 feet below the seafloor off the coast of Newfoundland. They contain materials representing a geological record dating back millions of years. A 26-foot layer stood out, capturing extensive geomagnetic reversals in remarkable detail.

After several years of analysis to determine whether the anomaly resulted from magnetic changes or sedimentary disturbances, the researchers confirmed two long reversals during the Eocene about 40 million years ago, one lasting about 18,000 years and the other about 70,000 years.

Real-world evidence confirms computer simulations

Experts still don’t know what triggers a reversal. What they TO DO What I do know is that they “don’t last the same amount of time,” creating a “unique barcode” in the sediment, Lippert said in the release. “We can use the magnetic directions preserved in the sediments and correlate them on the geological time scale.”

The research provides long-awaited evidence for predictions made by computer models of Earth’s magnetic field. Scientists had previously proposed the existence of occasional long transitions, but only theoretically through simulations, with some scenarios lasting up to 130,000 years.

Learn more: An increasingly weak point in Earth’s magnetic field could cause more satellites to short circuit

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