Ancient kauri trees capture the last collapse of Earth’s magnetic field

A few years ago, workers digging for a power plant in New Zealand found a 60-ton trunk of a kauri tree, New Zealand’s largest tree species. The 42,000-year-old tree is preserved in a swamp, and its rings date back 1,700 years, reflecting the reversal of the Earth’s magnetic poles.

Radiocarbon levels in this and several other pieces of wood point to a surge of radiation from space as the Earth’s protective magnetic field weakened and its poles flipped, a team of scientists report today in the journal Science. By modeling the effect of this radiation on the atmosphere, the team suggests that Earth’s climate changed briefly, possibly contributing to the extinction of large mammals in Australia and Neanderthals in Europe. “We’re only scratching the surface of what geomagnetic changes have done,” says Alan Cooper, an ancient DNA researcher at the Museum of South Australia and one of the study’s lead authors.