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

New research reveals some magnetic field reversals take significantly longer than previously thought, weakening Earth's protection from cosmic radiation.

Published on Feb. 9, 2026

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Earth's magnetic field, which protects the planet from harmful cosmic radiation, regularly flips its polarity. While most reversals were thought to last around 10,000 years, a new study has found evidence of some reversals lasting as long as 70,000 years. Researchers analyzed deep-sea sediment cores and confirmed two lengthy reversals during the Eocene epoch about 40 million years ago, providing real-world evidence for computer simulations that had predicted the existence of occasional long magnetic field transitions.

Why it matters

Earth's magnetic field is critical for shielding the planet from solar radiation and other harmful particles from space. Extended periods of magnetic field instability and weakening can influence atmospheric chemistry, climate, and even the evolution of organisms by exposing them to higher levels of cosmic radiation. Understanding the full range of magnetic field reversal durations is important for modeling the impacts on the environment and life.

The details

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 in a process known as geomagnetic reversal that typically lasts several thousand years. During this time, the magnetic field destabilizes, reducing the strength of the geomagnetic shield. The new study analyzed deep-sea sediment cores retrieved off the coast of Newfoundland and found evidence of two lengthy reversals during the Eocene epoch about 40 million years ago - one lasting roughly 18,000 years and another about 70,000 years.

  • The sediment cores analyzed represent a geological record stretching back millions of years.
  • The two lengthy reversals occurred during the Eocene epoch, about 40 million years ago.

The players

Peter Lippert

Associate professor in the Department of Geology and Geophysics at the University of Utah.

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What they’re saying

“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.”

— Peter Lippert, Associate professor (University of Utah press release)

“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.”

— Peter Lippert, Associate professor (University of Utah press release)

The takeaway

This research provides important new insights into the full range of Earth's magnetic field reversal durations, with some reversals lasting significantly longer than the previously understood 10,000-year timeframe. Understanding these extended magnetic field instability periods is crucial for modeling the potential impacts on the environment, climate, and the evolution of life on Earth.