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252 million years ago, the world was experiencing a turbulent period of rapid global warming.
Scientists have examined one event that emitted large amounts of greenhouse gases into the atmosphere as a way to understand why it happened. It was a volcanic eruption in Siberia.
However, evidence suggests that the climate has been changing long before this.
Sea surface temperatures had increased by more than 6–8℃ in the hundreds of thousands of years leading up to the Siberian outpouring. Temperatures increased again after it, so much so that 85–95% of all living species eventually went extinct.
Although the Siberia eruption clearly left a mark on the planet’s surface, experts remain puzzled as to what caused the initial warming.
Our research reveals Australia’s own ancient volcanoes played a big role. Before the Siberia event, volcanic ash was emitted from the east coast by catastrophic eruptions in New South Wales.
These eruptions were so large they initiated the world’s biggest ever climate catastrophe — the evidence for which is now hidden deep in Australia’s thick piles of sediment.
Ancient volcanoes
Our study Today’s publication in Nature, confirms eastern Australia was shaken by repeated “super eruptions” between 256 and 252 million years ago.
Super eruptions are very different to the passive Siberian event. These explosions caused massive amounts of ash to be emitted high into the atmosphere.
This is evident in the light-colored layers of volcanic ash in sedimentary rocks. These layers are found all over NSW and Queensland, including near Townsville.
Ian Metcalfe
Our study has revealed the source of this ash in New England, NSW. There the eroded remains from volcanoes have been preserved.
Although erosion has erased much of the evidence, the innocuous-looking rocks remain as a record of terrifying eruptions. It is consistent with the largest known volcanic eruptions because of the thickness and extent of the ash produced.
Tim Chapman
How large were super eruptions?
At least 150,000 km³ of material erupted from the northern NSW volcanoes over four million years. These supervolcanoes are similar to those of Yellowstone in the United States or Taupo in New Zealand.
To put it into perspective, the 79AD eruption of Mt Vesuvius, which obliterated the Italian city of Pompeii, produced just 3–4km³ of rock and ash. And the deadly Mt St Helens eruption in 1980 was about 1km³.
The Australian eruptions would have repeatedly covered it Complete east coast in ash — metres thick in some places. A massive outpouring in greenhouse gases would have caused global climate change.
Environmental devastation
An overview of the environmental damage that was caused by volcanic eruptions can be found in ancient sedimentary rocks. Ironically, the evidence can be preserved in coal measures.
Today’s coal deposits in eastern Australia show ancient forests used to cover much of this land. After the super eruptions, however, these forests were abruptly terminated in a series of bushfires over some 500,000 years, 252.5–253 million years ago.
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Typically, the plant matter was buried under sediments after it had accumulated in swamps. The burial process provided heat, pressure, and enabled the conversion of plant matter into coal.
Without forests, there would be no plant matter to accumulate. The ecosystem collapsed, and most animals went extinct.
The subsequent eruptions in Siberia only exaggerated the devastation started by Australia’s supervolcanoes.
This collapse of ecosystems wasn’t just limited to Australia. All of the ancient continents were affected by this catastrophic event. It had a substantial influence on the evolution of life — which eventually led to the rise of the dinosaurs.
Australia’s super eruptions were a key marker of change in the ancient world. We are now aiming to achieve a more sustainable climate in the future. But who knew that the clues to environmental disaster lay beneath our feet?
Acknowledgement: We would like to acknowledge Phil Blevin, Geological Survey of New South Wales, for his contribution to this project.
