Scientists studying an extraordinary ancient tree in New Zealand have uncovered fresh insights into one of Earth’s most dramatic magnetic disturbances – and what it means for our future.
A massive buried tree of the species Agathis australis (kauri), discovered near Ngāwhā in the Northland region of New Zealand, lived between about 41,000 and 42,500 years ago. During that time, our planet experienced the event known as the Laschamp Excursion, when the Earth’s magnetic poles wavered dramatically but did not fully reverse. The tree’s long, well-preserved growth rings offer an unprecedented, high-resolution record of how the magnetic field behaved during that period.
A Tree That Captured Earth’s Magnetic Drama
The tree—estimated at roughly 1,700 years of growth—was buried in wet, low-oxygen sediments, which kept its wood remarkably intact, including bark and growth rings. Researchers were able to date its rings precisely and trace changes in radiocarbon levels in the atmosphere. These changes reflect the collapse of the magnetic field, which normally shields Earth from cosmic radiation.
The findings show that during the lead-up to the magnetic excursion (sometimes dubbed the “Adams Event” in the study), the geomagnetic field strength dropped to an estimated 0–6 % of its present-day level. At its low point, Earth’s protective magnetic shield was essentially gone for a short time.
Why It Matters: Climate, Life & Technology
With the magnetic field so severely weakened, cosmic radiation bombarded Earth’s upper atmosphere. The tree-ring radiocarbon record indicates a spike in radiocarbon production—evidence of diminished shielding from cosmic rays.
Researchers link this event to abrupt climate changes: shifts in wind patterns, glacial activity, and even the extinction of large animals in Australia and Tasmania around the same time.
The event may also explain one of our species’ more mysterious turns: the sudden proliferation of cave art around 42,000 years ago. With UV levels rising and auroras sweeping across skies as far as the equator, early humans may have sought shelter in caves. The red ochre handprints found in many ancient caves might have served as a rudimentary form of sun-protection.
Could It Happen Again?
Yes—and that’s part of the warning in the study. Our current magnetic field is weakening gradually, and the north magnetic pole has been moving rapidly in recent decades. While a full pole reversal is not certain, this ancient record shows the kind of dramatic change that is possible—and the wide-ranging consequences.
For modern society, a sudden collapse of the magnetic field could be catastrophic: satellites and power grids may be vulnerable, radiation exposures could rise, and climate systems might shift in unpredictable ways.
The Key Take-away
This giant kauri tree gives us a direct window into how Earth responds when its magnetic shield falters. The tree’s rings record a moment when our planet’s magnetic field almost collapsed—not just a scientific curiosity, but a cautionary tale. The message: while we cannot forecast exactly when or how the next big change might come, the potential effects are clear and dramatic.
Source
Cooper, A. et al. (2021). A global environmental crisis 42,000 years ago. Science. DOI:10.1126/science.abb8677.