By Laura Nichol
Steve Grasby on site at Buchanan Lake, Nunavut.
The largest extinction event in earth's history occurred in the Permian period 252 million years ago, when 95 percent of all marine species and 70 percent of all species on land became extinct. It occurred 185 million years before – and was much worse than – the popularly known extinction event that killed off the dinosaurs. After the colossal devastation of the Permian age, earth's ecosystems were fundamentally altered, and life reverted to its earliest phase of simple microbial organisms.
Many have thought the cause may have been a massive volcanic eruption in western Siberia, which took place at the same time as the extinction and is the largest eruption known.
Researchers from Natural Resources Canada (NRCan)'s Geological Survey of Canada (GSC) and the University of Calgary have now discovered the first concrete evidence supporting this theory. Layers of coal fly ash – finely particulate air-borne ash – have been found in rock from the Canadian High Arctic dating back to the Permian period, suggesting that the Siberian volcano triggered massive explosions of coal rock that spewed toxic fly ash into the atmosphere.
The Rocks Tell the Story
Roxane Dery collecting samples of shale rock deposited right after the extinction event at Buchanan Lake.
The evidence lies within 80 metres of black shale at Buchanan Lake, Nunavut. The researchers analyzed rock samples with specialized microscopes that make organic particles easy to detect. They found particles that looked identical to modern-day coal fly ash – a toxic byproduct of coal-burning power plants that is captured through filtration systems.
Fly ash would also have been a byproduct of massive coal explosions during the Siberian volcanic eruption, when hot lava – still visible today in the form of rock basalts – burned areas with thick deposits of coal and organic matter. The power of the explosions would have pushed the ash far into the atmosphere, from which it would have settled at Buchanan Lake and elsewhere.
Three separate layers of coal fly ash were found at Buchanan Lake, suggesting there were three distinctively massive explosive events. “Just like today, jet stream winds were westerly, so they would blow east across the globe,” explains Steve Grasby, a research scientist with the Geological Survey of Canada. “These three enormous explosions were large enough to billow ash into the atmosphere 20 000 kilometres east around the earth, depositing them in what is now known as Arctic Canada”.
Linking Coal Ash Deposits and the Extinction
Under a specialized microscope, an organic particle from shale samples found at Buchanan Lake shows remarkable similarities to that of modern-day coal fly ash.
The rapid and large-scale production of coal ash would have created several environmental conditions that could have contributed to the Permian extinction:
Global warming: The rock record shows significant global warming during this time. Some propose that the combination of CO2 emissions from the volcanic eruption and the burning of massive amounts of coal led to a runaway greenhouse gas effect. This theory may partly explain why the oceans lost their oxygen and became anoxic, a phenomenon detrimental to marine organisms because the oceans become hotter and toxic hydrogen sulphide gas is formed.
Ocean toxicity: The rock record also shows dramatic spikes of toxic metals found in fly ash at the time of the extinction. These metals would have had devastating consequences on marine ecosystems.
Preventing photosynthesis: Deposits of coal ash in the ocean would have created a floating sludge that blocked out sunlight, which is essential for photosynthesis by marine plant life and for the functioning of broader marine ecosystems.
Still, much remains unknown. “It's not clear what the ultimate driver was,” says Steve. “But it was likely the combination of multiple environmental changes occurring at the same time that led to the worst extinction in earth's history.”
But although many details are unclear, the discovery of the coal ash deposits provides the first concrete evidence that the great Siberian volcanic eruption may have caused this significant event.
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