Burning coal is nasty business, concentrating all kinds of toxic metals and resulting in potentially deadly fly ash. That's why stretches of the Emory and Clinch rivers in Tennessee essentially died when flooded with coal ash slurry two years ago.

Now imagine that happening on an apocalyptic scale: millennia-long volcanic eruptions setting on fire--even exploding--massive coal deposits in present day Siberia. That's what some scientists think may have set off the Permian mass extinction some 250 million years ago.

Roughly 90 percent of all ocean life died as a result. It was the end for ammonites and trilobites. Life itself may have barely survived the most devastating mass extinction event known to science, hence its name: the "Great Dying." And the reason could be coal ash, according to new research published in Nature Geoscience. (Scientific American is part of the Nature Publishing Group.)

Canadian geologists have found evidence of coal char--"remarkably similar to modern coal fly ash" in their own words--in ancient Arctic rocks. Given the toxic impact of modern coal fly ash on aquatic ecosystems, the scientists suggest that the massive coal conflagration may have created toxic marine conditions the world over.

Of course, humanity is currently setting off the sixth mass extinction event in Earth's history. And a big part of that is from burning coal, both the CO2 it releases that then causes climate change as well as all that fly ash. We may just be following Mother Nature's ancient recipe.

—David Biello