Mass deaths due to increased UV radiation

mass extinction
Malformations of spiny structures on the surface of fossil plant spores (right) are interpreted by researchers as signs of UV damage. (Image: John Marshall)

What caused the mysterious “Hangenberg crisis” 360 million years ago? A temporary collapse of the Earth’s ozone layer may have been responsible for this mass extinction. This is the study of fossil plant spores that show damage from ultraviolet radiation. As the scientists explain, a result of global warming, more ozone-depleting substances may have entered the upper atmosphere at the end of the Devon Age. They see it as an indication that similar processes could also occur due to current climate change.

The evolution of life on our planet has been marked by a continuous coming and going of species – but there have also been drastic cuts in which an enormous number of animal and plant species disappeared in a short period of time. The most famous of these mass extinctions ended the age of dinosaurs. While in this case an asteroid impact 66 million years ago is considered the cause, increased volcanism seems to have been the trigger for the other known extinction events: there is evidence that massive eruptions have led to atmospheric and oceanic changes that a large part of the living beings has been unable to cope with.

On the trail of a mysterious mass extinction

However, the cause of the mass extinction at the Devon-Carbon border remains unclear. In the course of this so-called Hangenberg crisis some 359 million years ago, a large part of the plants and especially the freshwater animals died out, according to finds in various places around the world. As the researchers led by John Marshall of the University of Southampton explain, geological research shows that there were no volcanic activities with global consequences during this time. However, it seems that the Hangenberg crisis is coming at a time after the rapid warming that ended the last devon ice age.

As part of their study, Marshall and his colleagues have now studied fossil spores of colorful plants that deposited during the time in question. They come from rock samples collected by the team during expeditions in East Greenland. As the scientists explain, 359 million years ago there was a huge lake bed that was still in the equatorial area at the time. It was part of the landmass that was once formed from what is now Europe and North America. Back in the lab, the researchers dissolved the primeval sedimentary rocks into acid, releasing the remnants of the sometimes surprisingly well-preserved plant spores.