Mass Extinction
© Stephen Grasby , Postmedia News
Researchers walk through sediments deposited shortly after the worst extinction event in Earth history, on the shores of Buchanan Lake, Axel Heiberg Island, Nunavut.
Canadian scientists probing two sites in the High Arctic have found fresh evidence pointing to a fiery Siberian suspect in the greatest mass extinction of all time - a planet-wide cataclysm that wiped out more than 90 per cent of the Earth's species about 250 million years ago.

The so-called "Great Dying" at the end of the Permian geological era killed off a larger proportion of species than any of the 25 other mass extinctions scientists have identified from sudden and widespread gaps in the fossil record at certain layers of rock corresponding to specific periods of time.

The precise cause of the biological catastrophe 252 million years ago has been debated by scientists for decades. But nothing else in Earth history compares to the Late Permian disaster, which eclipsed 95 per cent of all marine life and about 70 per cent of species on land.

Some have argued that a massive meteorite strike - like the one widely presumed to have triggered the end of the dinosaur age 65 million years ago - must have been to blame. Others point to extreme climate change linked to ocean acidification, oxygen depletion, mercury poisoning or other species-snuffing effects as the main driver of the extinctions.

And without discounting the other forces as potential contributors to the Great Dying, a growing number of scientists - including several groups of Canadian researchers who are among the world's leading investigators of the die-off - have fingered a prolonged series of enormous volcanic eruptions in northern Asia known as the "Siberian Traps" as the main culprit in the Permian extinction.

The latest clues in the prehistoric puzzle, which reinforce the volcanism theory, come from Ellesmere Island and nearby Axel Heiberg Island in the Canadian Arctic, where five researchers from the University of Calgary and the Geological Survey of Canada have found evidence undercutting the idea that oxygen depletion occurred uniformly throughout the world's oceans and may have been the prime agent of death in the Great Dying.

At Axel Heiberg's Lake Buchanan and Ellesmere's West Blind Fiord, geological sites offering two of the best-known windows on the Permian extinction, the Canadian team tested rock samples for the element molybdenum - a "powerful tracer" used in reconstructing the oxygen levels of ancient marine environments - to better understand what was happening in waters off the coast of the supercontinent Pangea 252 million years ago.

At that time, the now-exposed Lake Buchanan and West Blind Fiord sites were lying at the bottom of the primordial ocean close to the equator.

The researchers, led by U of C geoscientist Bernadette Proemse, determined that the Lake Buchanan site - which preserves a deep-water seabed environment from the time of the Great Dying - showed clear signs of "anoxia" or extreme oxygen deprivation.

But the shallower Permian seafloor found at West Blind Fiord, which preserves a stretch of Pangea's extinction-era continental shelf, showed a fairly well-oxygenated marine environment even as the Great Dying was unfolding.

In short, the findings confirm oxygen starvation as a significant factor in some phases or sites of the global crisis, but rule it out as the underlying cause of the planet-spanning extinctions, the researchers conclude.

Their study was published in the latest issue of the journal Geology.

"It is clear that anoxia cannot be the direct cause of the extinction," the scientists argue, pointing to the oxygenated seawater available at the Ellesmere Island site. "Rather than the direct cause of global extinction, anoxia may be more a contributing factor along with numerous other impacts associated with Siberian Traps eruption and other perturbations to the Earth system."

The impacts from the Siberian eruptions, "the largest volcanic event in Earth history, are increasingly recognized as devastating to global ecosystems" at the end of the Permian era, the researchers added. "Widespread anoxic conditions are more likely a symptom of other external factors placing multiple stresses on the global environment due to massive eruptions of the Siberian Traps at that time."

Traces of the ancient volcanic calamity itself can be seen across a wide area of present-day Russia near the Siberian city of Norilsk.

The researchers involved in the new Geology study have published previous papers on the Permian extinction. Co-authors Stephen Grasby, a GSC geologist who also teaches at the University of Calgary, and fellow U of C scientist Benoit Beauchamp collaborated on a 2011 research project that pointed to layers of coal ash found at Lake Buchanan as "smoking gun" proof that the fiery Siberian Traps were wreaking havoc on the global climate and suffocating life almost everywhere around the world.

In 2008, another team of Canadian scientists announced the discovery of a thin band of rock running through B.C., Alberta and Arctic Canada that appears to have served as a rare coastal refuge for life during the Great Dying.

The refuge was identified by its diverse and abundant deposits of fossils, proof that a "thriving" array of clams, worms and other seabed species endured in at least one narrow strip of ancient Canada at time when nearly all of the world's other terrestrial and marine ecosystems had become poisonous to life.