(ORDO NEWS) — About 252 million years ago, the world was going through a turbulent period of rapid global warming.
To understand its cause, scientists drew attention to one specific event, when a volcanic eruption in what is now Siberia released a huge amount of greenhouse gas into the atmosphere.
However, there is evidence that the climate was already changing before that.
In the hundreds of thousands of years preceding the Siberian eruption, the sea surface temperature increased by more than 6-8 ℃. After it, the temperature rose again, so much so that 85-95 percent of all living species eventually became extinct.
An eruption in Siberia certainly left its mark on the planet, but experts remain puzzled as to what caused the initial warming that preceded it.
Our study showed that the ancient volcanoes of Australia played a big role. Prior to the events in Siberia, catastrophic eruptions in northern New South Wales spewing volcanic ash onto the east coast.
These eruptions were so massive that they set off the world’s largest climate catastrophe, the evidence of which is now hidden deep in the sedimentary rocks of Australia.
Our study, published today in the journal 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 events. These catastrophic explosions spewed huge amounts of ash and gases high into the atmosphere.
Today we see evidence of this in the form of light-colored layers of volcanic ash in sedimentary rocks. These layers are found in vast areas of the states of New South Wales and Queensland, all the way from Sydney to the outskirts of Townsville.
Our study identified the source of this ash in the New England region of New South Wales, where volcanic eruption remains.
Although erosion has removed much of the evidence, these harmless-looking rocks are evidence of horrific eruptions. The thickness and spread of the resulting ash is consistent with the largest known volcanic eruptions.
How big were these super-eruptions?
Over 4 million years, at least 150,000 km³ of material has erupted from northern NSW volcanoes. This makes them similar to the supervolcanoes of Yellowstone in the US and Taupo in New Zealand.
For comparison, the eruption of Mount Vesuvius in 79 AD, which destroyed the Italian city of Pompeii, produced only 3-4 km³ of rock and ash. And the deadly eruption of Mount St. Helens in 1980 was about 1 km³.
Australian eruptions could repeatedly cover the entire east coast with ash – in some places its thickness reached meters. A massive release of greenhouse gases would cause global climate change.
Devastation of the environment
Ancient sedimentary rocks give us a timeline of the ecological damage caused by eruptions. Oddly enough, evidence of this has been preserved in coal rocks.
Today’s coal deposits in eastern Australia are evidence that ancient forests covered much of this land. However, after the supereruptions, these forests came to an abrupt end in a series of bushfires over the course of approximately 500,000 years, 252.5-253 million years ago.
As a rule, plant mass accumulated in swamps, and then was buried under sedimentary rocks. The burial process provided heat and pressure, which allowed the plant mass to be turned into coal.
Without forests, plant mass did not accumulate. The ecosystem collapsed and most of the animals died out.
Subsequent eruptions in Siberia only exacerbated the destruction started by the Australian supervolcanoes.
And this collapse of ecosystems was not limited to Australia. The catastrophic event affected all the ancient continents. It had a significant impact on the evolution of life, which ultimately led to the appearance of dinosaurs.
Super eruptions in Australia were a key marker of change in the ancient world. We strive to achieve a more livable climate in the future, but who would have thought that the key to environmental disaster is lurking under our feet?
Acknowledgments: We would like to thank our colleague Phil Blevin of the Geological Survey of New South Wales for his contributions to this work.
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