Ancient Trees Show When The Earth's Magnetic Field Last Flipped Out

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.  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. - NPR / Science

A giant kauri tree grows in Waipoua Forest in Northland, New Zealand. Trees like this one that fell long ago and were preserved for thousands of years are helping researchers discern fluctuations in the Earth's magnetic poles.