The Earth’s magnetic field is what keeps the Sun’s hazardous radiation and high-energy particles from causing problems to the biosphere, such as cancer or damaging the electrical grid. The field is generated by the rotation of Earth’s iron-rich molten outer core around the solid inner core. The magnetic field flows around the Earth from bottom to top, concentrating at these locations. These are called the poles, and on Earth, our magnetic field current flows from the North Pole to the South Pole.
Your everyday magnet you might use in science class has two poles as well. Venus and Mars are thought to have had magnetic fields in the same way but no longer do. Jupiter’s moon, Ganymede, is the only other rocky body in our solar system with a magnetic field similar to Earth’s.
Interestingly, the Earth’s poles have flipped many many times over the fullness of geology history – meaning the field lines flow in the opposite direction, in this case from South to North. We know this because the orientation of the poles is preserved in magnetic basalts produced at ocean floor spreading ridges. As you head away from these ridges, the rocks get older, and the polarity changes back and forth. Usually, the polarity changes every two hundred thousand years or so, and scientists are monitoring the start of the next reversal. Or maybe not, according to new research in the Proceedings of the National Academy of Science.
The South Atlantic Anomaly (SAA) is another key thing to understand about the Earth’s magnetic field. It’s an area of weakness in the magnetic field centered off the coast of South America that causes satellites in Low Earth Orbit to have problems if they pass through it.
Now, researchers have combined several different methods to make a history of the Earth’s entire magnetic field in direction and intensity over the last nine thousand years. These methods included analyzing old, fired pottery, the previously mentioned volcanic rocks, and sediments. And it turns out that human artifacts can tell us more than just how people lived in the past.
All of this data was used to create a model of the magnetic fields, and according to one of the researchers, Andreas Nilsson, the model “predict[s] that the South Atlantic Anomaly will probably disappear within the next 300 years and that Earth is not heading towards a polarity reversal”.
So the South Atlantic Anomaly is just the most recent magnetic phenomenon in a long history of ones, and the poles won’t be flipping anytime soon.
As a side note, this work is also helping archeologists perform more accurate dating of artifacts. Some methods for determining the ages of ancient objects involve using the magnetic field, and by comparing the real magnetic field to the model, they can improve the model.
Lund University press release
“Recurrent ancient geomagnetic field anomalies shed light on future evolution of the South Atlantic Anomaly,” Andreas Nilsson, Neil Suttie, Joseph S. Stoner, and Raimund Muscheler, 2022 June 6, PNAS