Some 252 million years ago, the world was going through a tumultuous period of rapid global warming.
To figure out what caused it, scientists looked at a particular event in which a volcanic eruption in what is now Siberia spewed huge volumes of greenhouse gases into the atmosphere. However, there is evidence that the climate was already changing before that. Sea surface temperatures had risen more than six to eight degrees Celsius in the hundreds of thousands of years before the Siberian outpouring. Temperatures rose again after that, so much so that 85-95% of all living species eventually died out.
The eruption in Siberia obviously scarred the planet, but experts remained puzzled as to what caused the initial warming that preceded it. Our research reveals that ancient Australian volcanoes played a big role. Prior to the event in Siberia, catastrophic eruptions in northern New South Wales spewed volcanic ash onto the east coast. These eruptions were so large that they triggered the world’s greatest climate catastrophe, evidence of which is now hidden deep in Australia’s thick piles of sediment.
Our study, posted last week in Nature, confirms that eastern Australia was rocked by repeated “super eruptions” between 256 and 252 million years ago. Super eruptions are different from the more passive Siberian event. These catastrophic explosions spewed massive amounts of ash and gas into the atmosphere.
Today we see evidence of this in layers of light-colored volcanic ash in sedimentary rock. These layers are found over large areas of NSW and Queensland, from Sydney to Townsville.
Our study identified the source of these ashes in the New England region of New South Wales, where the eroded remains of volcanoes are preserved. Although erosion has removed much of the evidence, the now harmless rocks are our record for terrifying eruptions. The thickness and spread of the ash produced matches some of the largest known volcanic eruptions.
How big were the super flares?
At least 150,000 cubic kilometers of material erupted from volcanoes in northern New South Wales over four million years. This makes them similar to the supervolcanoes of Yellowstone in the United States and Taupo in New Zealand.
To put things into perspective, the eruption of Vesuvius in AD 79, which wiped out the Italian city of Pompeii, produced only three to four cubic kilometers of rock and ash. And the deadly eruption of Mount St Helens in 1980 was around one km³.
Australian eruptions are reported to have repeatedly covered the entire east coast in ash — several meters thick in places. And a massive outpouring of greenhouse gases would have triggered global climate change.
Ancient sedimentary rocks provide us with a timeline of environmental damage caused by eruptions. Ironically, the evidence is preserved in the coal measurements.
Today’s coalfields in eastern Australia show ancient forests used to cover much of this land. After the super eruptions, however, these forests abruptly ended in a series of bushfires over about 500,000 years, 252.5 to 253 million years ago.
Typically, plant material accumulated in swamps and was then buried under sediment. The burial process provided heat and pressure that enabled the conversion of plant material into charcoal. Without forests, there was no plant matter to accumulate. The ecosystem collapsed and most animals disappeared. Subsequent eruptions in Siberia have only exaggerated the devastation wrought by Australia’s supervolcanoes.
And this collapse of ecosystems was not limited to Australia either. The catastrophic event affected all the ancient continents. He had a tremendous influence on the evolution of life, which ultimately led to the rise of dinosaurs.
Australian super eruptions were a key marker of change in the ancient world. As we seek to achieve a more habitable climate in the future, who knew the clues of environmental catastrophe were buried beneath our feet?
Acknowledgements: We would like to thank our colleague Phil Blevin from the Geological Survey of New South Wales for his contribution to this work.
Image credit: ELG21 / 1625 images