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

[Kreigh Tomaszewski]

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 Neandertals. 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
<https://science.sciencemag.org/cgi/doi/10.1126/science.abb8677>, 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
<https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018RG000629> that
die-offs of large mammals seemed to occur in periods when the Earth's
magnetic field was weak.

https://www.npr.org/2021/02/18/969063568/ancient-trees-show-when-the-earths-magnetic-field-last-flipped-out