news @ nature.com - Plant pollen records ozone holes - Fossil measurements might reveals causes of mass extinction.:
There are many ideas about the Permian extinction, when almost 90% of all species died. "So far, no-one's come up with a definitive mechanism," says Andrew Saunders, a geochemist from the University of Leicester who has researched the event.
Some scientists think a comet or meteorite struck the Earth. Others link the event to an enormous volcanic eruption that left a large mass of lava in Siberia.
This eruption would have released dust, sulphur and halogen compounds, disrupting the chemistry of the atmosphere and possibly eating a hole in the ozone layer.
Spores from the time show severe mutations, which may have been caused by ultraviolet radiation let through by a thinner ozone layer1. But at the moment there's no conclusive evidence of an ozone loss at that time, says Barry Lomax, part of the Sheffield team, who presented the team's results on 10 August at the Earth System Processes conference in Calgary, Canada.
"We hope this method will be the first independent test of ozone levels from that period," says Wellman. There is an excellent fossil record of pollen spores, and although the para-coumaric acids break down over time, they leave signature chemicals that should remain in fossils that have not been heated, he says.
"If it works, we should see a massive increase in pigments during the Permian," says Wellman. With a thinner ozone layer, more ultraviolet radiation would hit plants, forcing them to slather on more sunscreen.
The evolutionary response to an ozone hole tells us about the climate 252 million years ago, and about the causes of the extinction of 90% of the species alive at the time.