This latest great geomagnetic reversal set off a series of dramatic events that have far-reaching consequences for our planet. They read like the plot of a horror movie: the ozone layer was destroyed, thunderstorms swept through the tropics, solar winds generated spectacular light shows (auroras), arctic air spilled over North America, the layers of Ice and glaciers increased and weather patterns changed violently.
During these events, life on Earth was exposed to intense ultraviolet light, Neanderthals and giant animals known as megafauna became extinct, while modern humans sought protection in caves.
The magnetic north pole, where a compass needle points, has no permanent location. Instead, it generally wobbles near the geographic north pole, the point around which the Earth rotates, over time due to motions within the Earth’s core.
For reasons that are not entirely clear, the movements of the magnetic poles can sometimes be more extreme than wobble. One of the most dramatic migrations from these poles took place around 42,000 years ago and is known as the Laschamps Excursion, named after the town where it was discovered in the French Massif Central.
The Laschamps Excursion has been recognized around the world, including the most recent in Tasmania, Australia . But until now, it was not clear if such magnetic changes had any impact on the climate and life on the planet. Our new work brings together multiple lines of evidence that strongly suggest that the effects were indeed global and far-reaching.
Ancient trees
To investigate what happened, we analyzed ancient New Zealand kauri trees that have been conserved in peat bogs and other sediments for more than 40,000 years. Using the annual growth rings of kauri trees, we have been able to create a detailed timescale of how Earth’s atmosphere changed during this time. The trees revealed a prolonged spike in atmospheric radiocarbon levels caused by the collapse of the Earth’s magnetic field when the poles shifted, providing a way to accurately link geographically widely dispersed records.