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For nearly 200 years, scientists have believed that the next reversal of the Earth’s geomagnetic field would occur in about two millennia, temporarily leaving the planet unprotected from damaging charged particles from the sun. But now, scientists from the Massachusetts Institute of Technology say earthlings have some more time before they have to worry.

They just aren’t sure how much time.

Huapei Wang, who led the study with colleagues from Rutgers University and France, said that although the intensity of Earth’s geomagnetic field is decreasing, it still is double the planet’s average over the past 5 million years. In other words, the intensity is decreasing, but it will take much longer for the next reversal to happen.

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The research was published in the Proceedings of the National Academy of Sciences on Monday.

“It makes a huge difference, knowing if today’s field is a long-term average or is way above the long-term average,” Wang said in a statement from MIT. “Now we know we are way above the unstable zone. Even if the [field intensity] is dropping, we still have a long buffer that we can comfortably rely on.”

When the intensity of the geomagnetic field reaches zero, the Earth’s north and south magnetic poles flip polarity, a process known as geomagnetic field reversal. The lack of intensity could last several thousand years before reaching a stable level again.

The weakening geomagnetic field could damage electronics, cause genetic mutations, and affect animals who use Earth’s polarity as their “internal compass,” the statement said.

On average, geomagnetic field reversals occur once every few hundred thousand years. However, the last flip was about 780,000 years ago, so according to Wang, we are actually overdue.

“Sometimes you won’t have a flip for about 40 million years; other times there will be 10 flips in 1 million years,” Wang said.

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About 40,000 years ago, the field’s intensity began to slowly increase, which brought it to the higher-than-average level it is at today, Wang said in a phone interview. Scientists estimate the intensity did not begin decreasing until about 2,000 years ago, and the rate of decrease greatly picked up speed over the last 200 years.

Even so, Wang said, it will take much longer than two millennia to reach a no-intensity zone. After all, he added, the geomagnetic field still needs to decrease to the historical average before it hits zero.

“What I can say is, if you keep a constant present-day decrease rate, it will take another 1,000 years for the field to drop to its long-term average,” Wang said. “From there, the field intensity may go up again. There’s really no way to predict what will happen after that.”


Felicia Gans can be reached at felicia.gans@globe.com.