Massive coal fires may have been the cause for the extinction of more than 90 per cent of marine species 250 million years ago, say Canadian geologists.
Research published online this week in Nature Geoscience speculates that volcanic eruptions in what is now Siberia, may have caused coal seams to ignite explosively, sending large amounts of highly toxic coal fly-ash into the atmosphere.
The resulting fallout would have poisoned the oceans and changed Earth's chemistry.
Lead author Dr Stephen Grasby of the Geological Survey of Canada, and colleagues, write that they discovered charred particles in Permian aged deep-sea sediments in the high Arctic. They say the particles strongly resemble coal fly ash, created when coal is burned.
At the same time, a large body of volcanic rock, known as the Siberian Trap basalts, was deposited. Grasby and colleagues believe the basalt eruptions may have set fire to coal seams, sending fly ash into the atmosphere in massive quantities.
Flood basalt eruptions begin with an explosive phase and can send plumes of ash more than 20 kilometres into the atmosphere. Some major eruptions have been known to exceed 40 kilometres. That would be enough to take ash into the high stratosphere.
Ash raining from the sky
Assuming this happened in the Permian eruptions, the light ash would have been dispersed globally on the prevailing winds before falling out of the stratosphere, write the researchers. It would then have settled very slowly in water, and formed a slurry that limited light penetration.
Naturally occurring toxic metals and radioactive elements which were concentrated in the ash would have produced highly poisonous, anoxic conditions.
The extra nutrients that the ash contained would have caused cyanobacteria to bloom, which is supported by other geological evidence for the period.
The team also analysed terrestrial carbon found in Permian deep-sea sediments from the Canadian high Arctic. They say the rocks "suggest a substantial amount of char was deposited ... immediately before the mass extinction."
They analysed the geochemistry and petrology of the char and say it could have derived from the combustion of Siberian coal and organic rich sediments.
"The char is remarkably similar to modern coal fly ash, which can create toxic aquatic conditions when released as slurries," Grasby and colleagues write.
During the Permian extinction, also known as the 'Great Dying', biogeochemical cycles were disrupted globally, the researchers write. Approxaimtely 80 per cent of all land based animals died out, along with 90 per cent of marine life.
They say their findings provide the first evidence for coal ash as a factor in the late Permian extinction event.