photo #8264713

An ancient kauri tree uncovered near Ngāwhā, Northland, New Zealand, has captured in its annual rings a detailed record of one of Earth’s most recent geomagnetic excursions—when magnetic north briefly swapped places with south approximately 42,000 years ago (New Atlas, Smithsonian Magazine). The perfectly preserved fossil, discovered during power-plant construction, spans a continuous 1,700-year interval that includes the entire excursion period (New Atlas). By analyzing radiocarbon (^14C) concentrations in its rings, researchers determined that Earth’s magnetic field plunged to about 28 percent of its modern strength—and dipped as low as 6 percent between 41,600 and 42,300 years ago—before rebounding in what they’ve dubbed the “Adams Transitional Geomagnetic Event” (Smithsonian Magazine, New Atlas). Modeling suggests that this collapse of the magnetosphere, coinciding with a lull in solar activity, severely thinned the ozone layer, unleashed high levels of ultraviolet radiation, and produced spectacular low-latitude auroras and raging electrical storms (Smithsonian Magazine, New Atlas). This breakthrough demonstrates trees’ value as precise archives of past space-weather events—and offers a sobering foreshadowing of what might occur if today’s weakening magnetic field continues toward a full reversal, posing significant risks to modern technology and ecosystems (New Atlas).