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Artistic impression of latitudinally more widespread aurora as an expected consequence of geomagnetic field strength much lower than today’s. Image: Huapei Wang (with material courtesy of NASA’s Earth Observatory).

New research from MIT shows that the Earth’s geomagnetic field intensity is double the long-term historical average, indicating that the current field intensity has a long way to fall before reaching an unstable level that would lead to a reversal.

The intensity of Earth’s geomagnetic field has been dropping for the past 200 years, at a rate that some scientists suspect may cause the field to bottom out in 2,000 years, temporarily leaving the planet unprotected against damaging charged particles from the sun. This drop in intensity is associated with periodic geomagnetic field reversals, in which the Earth’s North and South magnetic poles flip polarity, and it could last for several thousand years before returning to a stable, shielding intensity.

With a weakened geomagnetic field, increased solar radiation might damage electronics — from individual pacemakers to entire power grids — and could induce genetic mutations. A reversal may also affect the navigation of animals that use Earth’s magnetic field as an internal compass.

But according to a new MIT study in the Proceedings of the National Academy of Sciences, the geomagnetic field is not in danger of flipping anytime soon: The researchers calculated Earth’s average, stable field intensity over the last 5 million years, and found that today’s intensity is about twice that of the historical average.

This indicates that the current field intensity has a long way to fall before reaching an unstable level that would lead to a reversal.

“It makes a huge difference, knowing if today’s field is a long-term average or is way above the long-term average,” says lead author Huapei Wang, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “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.”

Flip-flopping through history

Earth has undergone multiple geomagnetic reversals over its lifetime, flip-flopping its polarity at random intervals.

“Sometimes you won’t have a flip for about 40 million years; other times there will be 10 flips in 1 million years,” Wang says. “On average, the duration between two flips is a few hundred thousand years. The last flip was around 780,000 years ago, so we are actually overdue for a flip.”

The most obvious sign of an impending reversal is a geomagnetic field intensity that’s significantly below its historical, long-term average — a sign that the planet is tipping toward an unstable state. While satellites and ground-based observatories have made accurate measurements over the last 200 years of the current field intensity, there are less reliable estimates over the last few million years.

Wang and his colleagues, from Rutgers University and France, sought to measure Earth’s paleomagnetic field using ancient rocks erupted from volcanoes on the Galapagos Islands — an ideal site, since the island chain is on the equator. As Earth’s magnetic field, in its stable configuration, is a dipole, the intensity of the field should be the same at both poles, and half that intensity at the equator.

Wang reasoned that knowing the paleomagnetic field intensity at the equator and the poles would therefore give an accurate estimate of the planet’s average historical intensity.

Read more here: Scitechdaily

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