An ancient kauri tree in New Zealand has provided a 42,000-year-old record of the Laschamp excursion, a temporary reversal of Earth’s magnetic poles. During this event, the magnetic field weakened to 28% of its strength, exposing the planet to intense cosmic radiation. Researchers analyzed the tree’s growth rings, uncovering a spike in radiocarbon levels and a detailed timeline of changes.

A transitional phase, called the Adams Event, saw the magnetic field drop to just 0-6% of its strength, causing major environmental shifts like ice sheet growth in North America, drier conditions in Australia, and possibly contributing to the extinction of Neanderthals and megafauna. Increased cosmic radiation during this time might explain the surge in cave art as humans sought shelter.

Scientists warn that if a similar event occurred today, it could devastate power grids, satellites, and trigger rapid climate change. Understanding these past events highlights the fragility of our planet’s magnetic shield.