When north goes south: Is Earth’s magnetic field flipping?
It’s been 780,000 years since this occurred, and some scientists believe the Earth’s magnetic poles are overdue for a change.
Something strange is going on with the Earth’s magnetic field. It has gradually weakened and shifted its magnetic north pole (where a compass points, not the geographic north pole) from the Canadian Arctic to Siberia over the last 200 years. However, in recent decades, the slow shift south has accelerated, reaching speeds of up to 30 miles per year (48 kilometers per year). Could we be on the verge of a geomagnetic reversal, in which the magnetic north and south poles reverse positions?
The magnetic field of Earth is produced by the convection of molten iron in the planet’s core, approximately 1,800 miles (2896 km) beneath our feet. This superheated liquid generates electric currents, which cause electromagnetic fields to form. While the processes that cause pole reversal are relatively unknown, computer simulations of planetary dynamics show that the reversals occur on their own. The Sun’s magnetic field, which reverses every 11 years, lends support to this theory.
Our own magnetic field formed at least 4 billion years ago, and the Earth’s magnetic poles have reversed numerous times since then. Over the last 2.6 million years alone, the magnetic field switched ten times — and, because the most recent occurred a whopping 780,000 years ago, some scientists believe we are overdue for another. But reversals are not predictable and are certainly not periodic.
Magnetic field mapping
Using volcanic rocks, researchers have mapped out the Earth’s magnetic field’s ancient history. When lava cools, the iron it contains becomes magnetized in the magnetic field’s direction. It’s possible to reconstruct the past behavior of the planet’s magnetism as it strengthened, weakened, or changed polarity by examining these rocks and using radiometric dating techniques.
Scientists use the magnetic properties of archaeological artifacts to track more recent magnetic changes. When our forefathers heated an ancient hearth or kiln containing iron to high enough temperatures, the magnetism realigned with the Earth’s magnetic field upon cooling. The Curie point is the point at which this happens. Some floor segments of an Iron Age building in Jerusalem, which was burned down by a Babylonian army in 586 B.C., have been studied.
However, measuring these archeological artifacts is difficult. For one thing, the magnetism in ancient objects is extremely weak — insufficient to move a compass needle. And if any object is repeatedly heated and cooled, several magnetic patterns will be superimposed. Finally, their dependability is contingent on the objects remaining in the same location where the heating occurred.
Despite these challenges, scientists have largely mapped modern changes in the magnetic field beneath Western Europe and the Middle East.
Turtles and salmon and whales, oh my!
Scientists are unsure of the exact consequences of a reversal — evidence from previous reversals is lacking — but they could be severe. Many animals, for example, use the Earth’s magnetic field to navigate during migration.
Juvenile loggerhead turtles emerge from underground nests on Florida beaches, swim out to sea, and travel far into the Atlantic Ocean (sometimes completely traversing it). After a long time, they return to the same Florida beaches where they were born. They navigate the 9,000-mile (14,494-kilometer) journey by detecting the strength and direction of the magnetic field. A reversal of the magnetic field would severely disrupt the lives of salmon, whales, birds, and other creatures that rely on Earth’s magnetism to navigate.
Furthermore, Earth is constantly bombarded by a stream of charged particles from the Sun as well as cosmic rays, mostly protons and atomic nuclei from deep space. The magnetic field weakens and becomes significantly less effective at shielding us from those particles in the period leading up to a reversal. While some geologists note that mass extinctions appear to be associated with these time periods, humans or our ancestors have been on Earth for millions of years. There have been many reversals during that time, and there is no obvious correlation with human development.
Tumultuous time for tech
The direct impact on humanity may be minor, but not on technology. Artificial satellites are used for navigation, television broadcasting, weather forecasting, environmental monitoring, and various forms of communication. Solar wind or cosmic rays colliding with electronic circuits could seriously disrupt these satellites if they are not shielded by a magnetic field. A weak magnetic field in the South Atlantic Ocean, known as the “South Atlantic Anomaly,” is already causing problems for satellites and could be a sign of things to come.
Recent geological research has suggested a possible explanation for the anomaly. Our Moon is widely assumed to have formed when Earth was struck by the planet Theia 4.5 billion years ago, but Theia’s remains have never been discovered. It appears that Theia’s remains may now be beneath our feet.
There are two massive volumes of rock buried deep within the Earth, each one millions of times larger (and expanding) than Mount Everest and denser and hotter than the rest of the Earth’s mantle. Scientists believe that these rock masses are Theia’s missing remains, and that they interfere with the convection of molten iron, resulting in the South Atlantic’s weak magnetic field.
Regardless, the severity of a magnetic reversal is determined by how long it takes to complete the reversal. It is possible that migratory creatures, as well as mankind, will be able to adapt if the climate slowly shifts over thousands of years. Meanwhile, we still have a lot to learn about what’s going on deep within our planet.