Using a remarkable record from a 42,000-year-old kauri tree preserved in a bog, researchers have peered into a tumultuous time when the world was turned upside down—at least magnetically speaking. ScienceMagArchives
. By modeling the effect of this radiation on the atmosphere, the team suggests Earth's climate briefly shifted, perhaps contributing to the disappearance of large mammals in Australia and Neanderthals in Europe."We're only scratching the surface of what geomagnetic change has done," says Alan Cooper, an ancient DNA researcher at the South Australian Museum and one of the lead authors of the study.
Earth's magnetic field is created by the flow of molten iron in the outer core, which is prone to chaotic swings that not only weaken the field, but also cause the poles to wander and sometimes flip entirely. The magnetic orientations of minerals in rock record long-lasting reversals, but can't capture the details of a flip lasting hundreds of years, like the one 42,000 years ago.
Spikes in radiocarbon indicated the magnetic field weakened to some 6% of its present day strength by 41,500 years ago. At that point the poles flipped and the field recovered some strength, before crashing and flipping back 500 years later. Cooper notes that not only was Earth's cosmic ray shield down; the Sun's was, too.suggests that, around this same time, the Sun was experiencing several"grand minima"—episodes of low magnetic activity.
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