A CLUE to the catastrophic chain of events that led to Earth鈥檚 largest-ever extinction has come from a sample of rock from the Dolomite mountains in Italy.
The Permian extinction some 250 million years ago wiped out more than 90 per cent of marine life and 70 per cent of terrestrial life. Huge volcanic eruptions in Siberia were thought to be the cause, but exactly how has remained a mystery.
Mark Sephton at Imperial College London and his colleagues discovered the remains of cellulose molecules, a building block of plants, in sedimentary rock from the Dolomites. Cellulose is eaten by soil microbes, so it doesn鈥檛 usually survive long enough to become embedded in rock records. 鈥淪omething catastrophic must have swept the soil into the sea, out of the microbes鈥� reach,鈥� Sephton says.
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He speculates that acid gases from the eruption rained down as sulphuric acid, which caused the bacterial population to plummet and helped fungi to flourish. The acid gases would also have depleted the ozone layer, letting in more UV radiation. As the terrestrial ecosystem changed, land plants began to die out, loosening the soil so it was washed into the oceans where it blocked out light and devastated marine life (Geology, vol 33, p 941).
With modern human activity putting soil under stress, the Permian extinction should be seen as warning, Sephton says. 鈥淪oil erosion caused the Permian extinction. We must be careful that we don鈥檛 reach a dangerous tipping point.鈥�
