Ancient trees hint at Earth's global environmental crisis 42,000 years ago

The findings were made possible with ancient New Zealand kauri trees, which have been preserved in sediments for over 40,000 years. The archaeological work and project lead have been performed by researchers at the South Australian Museum and the University of New South Wales. Scientists of the ETH atmospheric chemistry group, at the Zürich University of Applied Sciences and at the Physical Meteorological Observatory Davos analysed the atmospheric and climate impacts with global chemistry-climate modelling(1,2).

Environmental crisis 42.000 years ago

Using the ancient trees, the researchers could measure, and date, the spike in atmospheric radiocarbon levels caused by the collapse of Earth’s magnetic field. While scientists already knew the magnetic poles temporarily flipped around 41-42’000 years ago—the so-called ‘Laschamps Excursion’—it was unclear exactly how this affected life on Earth. Now, the researchers compared the novel, more accurate timescale with records from sites around the world and used it in global modelling, finding that the growth of ice sheets and glaciers over North America as well as large shifts in major wind belts could be traced back to the Laschamps Excursion. Across mainland Australia and Tasmania, the megafauna went through simultaneous extinctions.

Exposed to cosmic radiation

42’000 years ago, during the run-up to the last glacial maximum, a complete loss of the Earth’s magnetic protection shield against highly energetic particles from remote super novae—called galactic cosmic rays or GCRs—coincided with periods of a weak sun, similar to the Maunder Minimum in the late 17^th century.  As the solar wind, which also shields the Earth against GCRs, stalls during these Grand Solar Minima, this led to an additional loss of the Earth’s protection against GCRs, besides the frosty reduction of insolation.