The Earth's Magnetic Field And Global Climate Crisis

npr  |   An ancient, well-preserved tree that was alive the last time the Earth's magnetic poles flipped has helped scientists pin down more precise timing of that event, which occurred about 42,000 years ago.

This new information has led them to link the flipping of the poles to key moments in the prehistoric record, like the sudden appearance of cave art and the mysterious extinction of large mammals and the Neanderthals. They argue that the weakening of the Earth's magnetic field would have briefly transformed the world by altering its climate and allowing far more ultraviolet light to pour in.

 

Their provocative analysis, in the journal Science, is sure to get researchers talking. Until now, scientists have mostly assumed that magnetic field reversals didn't matter much for life on Earth — although some geologists have noted that die-offs of large mammals seemed to occur in periods when the Earth's magnetic field was weak.

The Earth is a giant magnet because its core is solid iron, and swirling around it is an ocean of molten metal. This churning creates a huge magnetic field, one that wraps around the planet and protects it from charged cosmic rays coming in from outer space.

 Sometimes, for reasons scientists do not fully understand, the magnetic field becomes unstable and its north and south poles can flip. The last major reversal, though it was short-lived, happened around 42,000 years ago.

This reversal is called the Laschamp excursion, after lava flows in France that contain bits of iron that are basically pointed the wrong way. Volcanic activity back then, during the flip, produced this distinctive iron signature as the molten lava cooled and locked the iron into place. Iron molecules embedded in sediments around the world also captured a record of this magnetic wobble, which unfolded over about a thousand years.

"Even though it was short, the North Pole did wander across North America, right out towards New York, actually, and then back again across to Oregon," says Alan Cooper, an evolutionary biologist with Blue Sky Genetics and the South Australian Museum. He explains that it "then zoomed down through the Pacific really fast to Antarctica and hung out there for about 400 years and then shot back up through the Indian Ocean to the North Pole again."