Every 200,000 to 300,000 years Earth’s magnetic poles reverse. What was once the north pole becomes the south, and vice versa. It’s a time of invisible upheaval.
The last reversal was unusual because it was so long ago. For some reason, the poles have remained oriented the way they are now for about three-quarters of a million years. A new study has revealed some of the detail of that reversal.
The study of the Earth’s magnetic field is called paleomagnetism. It involves the study of rocks and sediments and sometimes archaeological materials. Rocks that were once molten retain a record of the Earth’s magnetic field as they solidified. The related field of magnetostratigraphy studies the record of geomagnetic reversals that are contained in those rocks. By dating the rocks, researchers can construct a timeline of the Earth’s reversals.
The last reversal is named the Matuyama-Brunhes geomagnetic reversal after the co-discoverers: Bernard Brunhes, a French geophysicist, and Motonori Matuyama, a Japanese geophysicist. Over the years since its discovery, researchers have tried to understand exactly when it happened, and also how long it took.
www.universetoday.com