The earth's magnetic field won't flip in just 100 years, researchers have found.

Reversal could potentially wreak havoc with our electrical grid, generating currents that might take it down.

However, the new study says the weakening intensity observed in the last few hundred years is actually simply a recovery from an abnormal high.

The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. The field can be thought of as a huge bubble, protecting us from cosmic radiation and charged particles that bombard Earth in solar winds.

WHAT COULD HAPPEN? Such a reversal could potentially wreak havoc with our electrical grid, generating currents that might take it down. Earth's magnetic field protects life from energetic particles from the sun and cosmic rays, both of which can cause genetic mutations, a weakening or temporary loss of the field before a permanent reversal could increase cancer rates. The danger to life would be even greater if flips were preceded by long periods of unstable magnetic behavior, say the researchers. Advertisement

The new paper, in the Proceedings of the National Academy of Sciences, used a new technique to measure changes in the magnetic field's strength in the past and found that its long-term average intensity over the past five million years was much weaker than the global database of paleointensity suggests - only about 60 percent of the field's strength today.

'The field may be decreasing rapidly, but we're not yet down to the long-term average,' said Dennis Kent of Columbia University's Lamont-Doherty Earth Observatory and co-author of the study with his former student, Huapel Wang, now a post-doctoral research associate at MIT, and Pierre Rochette of Aix-Marseille Université.

Humans have lived through dips in the field's intensity before, and there are debates about whether reversals in the more distant past had any connection to species extinctions.

However, experts say today, we have something else today that would be affected by weakening of the magnetic field alone: technology.

The magnetic field deflects the solar wind and cosmic rays.

When the field is weaker, more radiation gets through, which can disrupt power grids and satellite communications.

The study's results fit expectations that the magnetic field's intensity at the poles should be twice its intensity at the equator.

In contrast, the time-averaged intensity calculated from the PINT paleointensity database doesn't meet the two-to-one, poles-to-equator dipole hypothesis, and the database calculation suggests that the long-term average intensity over the past 5 million years is similar to the field's intensity today.

The authors believe the difference is in how the samples are analysed.

They say the database, which catalogs paleointensity data from published papers, includes a variety of methods and doesn't clearly delineate data from two different types of magnetized mineral samples, tiny single-domain grains that come from sites that cooled quickly, like basalt glass on the outer edges of lava flows, and more common larger multi-domain grains found deeper inside lava whose magnetic behaviour is more complex and require a different type of analysis.

HOW THEY DID IT The La Cumbre volcano in Galapagos National Park For the new study, the scientists used ancient lava flows from sites near the equator and compared the paleointensity data with what had been regarded as an anomalously low intensity obtained by others from lavas from near the South Pole. As lava cools, iron-bearing minerals form inside and act like tiny magnets, aligning with the Earth's magnetic field. Scientists can analyze ancient lava to determine both the direction and the intensity of the magnetic field at the time the lava formed. They worked with a representative range from the past 5 million years using 27 lavas from the Galápagos Islands, about 1 degree of latitude from the equator. The results were then compared to those from 38 lavas with single-domain properties from a volcanic area near McMurdo Station in Antarctica, about 12 degrees from the South Pole. Advertisement

Earth's magnetic poles have reversed several hundred times over the past 100 million years, most recently about 780,000 years ago.

Some scientists believe a dip in the magnetic field's intensity 41,000 years ago was also a brief reversal.

When scientists recently began noticing a decline in the magnetic field - about 10 percent over the past two centuries - it led to speculation that another reversal could be coming.

That doesn't mean it would happen quickly, if it happens at all.

The magnetic field's intensity rises and dips without a clear pattern, only sometimes dipping far enough to become unstable and possibly reverse.

During a reversal, geomagnetic intensity declines during a transition period that typically lasts hundreds to thousands of years, then rebuilds.

The 'north pole' - that is, the direction of magnetic north - was reversed a million years ago. This map shows how, starting about 789,000 years ago, the north pole wandered around Antarctica for several thousand years before flipping 786,000 years ago to the orientation we know today, with the pole somewhere in the Arctic.

MAGNETIC CHANGES Earth's magnetic poles have reversed several hundred times over the past 100 million years, most recently about 780,000 years ago. Some scientists believe a dip in the magnetic field's intensity 41,000 years ago was also a brief reversal. Advertisement

When they averaged the geomagnetic intensity of each set, it revealed close to a two-to-one intensity difference between the polar site and the equatorial site.

The results show that the time-averaged geomagnetic field intensity over the past 5 million years is about 60 percent of the field's intensity today and aligns with the GAD hypothesis, both in direction and intensity.

Other studies using only single-domain basalt glass from the ocean floor have found a similar time-averaged intensity, but they did not have samples to test the polar-equator ratio.

The agreement helps to validate the new multiple-domain analysis technique, Kent said.

The lower time-averaged paleointensity also suggests a shorter average magnetopause standoff distance--the distance at which the Earth's magnetic field repels the solar wind.

The average is about 9 times the Earth's radius compared to nearly 11 times the Earth's radius today, according to the paper.