A magnetic field reversal 42,000 years ago may have contributed to mass extinctions.

A flip-flop of Earth’s magnetic poles between 42,000 and 41,000 years ago briefly but dramatically shrank the magnetic field’s strength — and may have triggered a cascade of environmental crises on Earth, a new study suggests.

With the help of new, precise carbon dating obtained from ancient tree fossils, the researchers correlated shifts in climate patterns, large mammal extinctions and even changes in human behavior just before and during the Laschamps excursion, a brief reversal of the magnetic poles that lasted less than a thousand years. It’s the first study to directly link a magnetic pole reversal to large-scale environmental changes, the team reports in the Feb. 19 Science.

During a reversal, Earth’s protective magnetic field, which shields the planet from a barrage of charged particles streaming from the sun, can lose strength (SN: 1/28/19). So some researchers have suggested that these flip-flops may be linked to extinction events (SN: 11/19/20). Read the free article.