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Earth saw a lot of commotion when its magnetic poles flipped 42,000 years ago.

Scientists have known about the flip since the late 1960s. Earth's magnetic poles aren't static - they're generated by electric currents from the planet's liquid outer core, which is constantly in motion. As of late, Earth's magnetic North pole has wandered considerably on a path toward northern Russia.

But for the most part, scientists didn't think the last pole flip had a major environmental impact. Sure, the planet's magnetic field got weaker, allowing more cosmic rays to penetrate the atmosphere, but plant and animal life wasn't known to have been greatly affected.

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A new study now suggests a more dramatic phenomenon occurred: The additional cosmic rays may have depleted ozone concentrations, opening the floodgates for more ultraviolet radiation in the atmosphere. Shifting weather patterns may have expanded the ice sheet over North America and dried out Australia, prompting the extinction of many large mammal species. A solar storm, meanwhile, might have driven ancient humans to seek shelter in caves.