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 harsh cosmic radiation. However, Earth’s magnetic field — essentially a gigantic dipole magnet — is in a constant state of flux and regularly flips its polarity. In fact, the next flip may be long overdue, as these reversals typically occur every few hundred thousand years.

Researchers previously believed the flipping process lasted around 10,000 years (a blink of an eye in geological terms) and is accompanied by a weaker shield against radiation that can affect the environment.

Now, researchers from Japan, France, and the U.S. have found evidence that some magnetic field reversals last significantly longer. A study published in Nature Communications Earth & Environment describes deep-sea sediment cores revealing that a magnetic field flip 40 million years ago took about 70,000 years to complete. Paleomagnetists say these findings expand our understanding of geomagnetic phenomena that are critical for shielding Earth from solar radiation and other harmful particles from space.

Read More: What Is the Sun's Magnetic Field and Why Is It Important?

When Magnetic Fields Flip

The generator behind Earth’s magnetic field is the liquid nickel-iron outer core, roughly 1,800 miles below the surface, where electrical currents create the field. Occasionally, Earth’s poles switch 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 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 the safety net against radiation from outer space, and that radiation is observed and hypothesized to do all sorts of things,” said Peter Lippert, associate professor in the Department of Geology and Geophysics at the University of Utah, in a press release.

He further explained that “it’s logical to expect that there would be higher rates of genetic mutation [and] atmospheric erosion” and that “it’ll change organisms’ ability to navigate” during extended exposure to cosmic radiation.

Scientists have observed roughly 540 polarity flips over the last 170 million years. While most were thought to last about 10,000 years, new analyses of North Atlantic sediment cores suggest that some transitions were far 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 extracted samples tells scientists the planet’s polarity at the time.

Researchers retrieved the sediment cores in 2012 from nearly 1,000 feet below the seafloor off the coast of Newfoundland. They contain material representing a geological record stretching back millions of years. One 26-foot layer stood out, capturing extended geomagnetic reversals in remarkable detail.

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

Real-World Evidence Confirms Computer Simulations

Experts still don’t know what triggers a reversal. What they do know is that they “don’t last the same amount of time,” creating a “unique barcode” in sediments, Lippert explained in the release. “We can use the magnetic directions preserved in the sediments and correlate them to the geologic timescale.”

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

Read More: A Growing Weak Spot in Earth's Magnetic Field May Cause More Satellites to Short Circuit

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

• This article references information from a recent study published in Communications Earth & Environment: Extraordinarily long duration of Eocene geomagnetic polarity reversals
• This article references information from a recent article published in Springer Nature: Extraordinarily long duration of Eocene geomagnetic polarity reversals