Fresh evidence gathered from ancient rocks on an Ellesmere Island fiord has led a 14-member international scientific team — including a University of Calgary researcher — to conclude that the greatest mass extinction in Earth's history unfolded slowly, possibly over a period of hundreds of thousands of years.
The latest discovery concerning the primordial calamity that happened about 250 million years ago, which also has been the focus of several Canadian-led research projects in recent years, sheds new light on the duration and intensity of the so-called "Great Dying," which experts previously had believed was a more sudden catastrophe that killed off about 90 per cent of all species on the planet.
Much of the scientific world's understanding of the Permian-Triassic extinction has come as a result of geological and paleontological findings in Canada's High Arctic islands, which preserve a high-resolution record of ash deposits and fossils showing the disappearance of many organisms at the time of a massive volcanic disaster in present-day Siberia.
Now, University of Calgary paleontologist Charles Henderson and 13 U.S. co-authors writing in the Geological Society of America Bulletin have offered a more nuanced explanation of how long it took when Earth "almost became a lifeless planet."
The findings prove "mass extinctions need not be sudden events," states a summary of the study issued by the National Science Foundation, the U.S. agency that funded the Arctic research along with NASA and Canada's NSERC research council.
Scientists have long believed that enormous amounts of noxious fallout from the Siberian volcanoes led to the mass extinction, with two recent Canadian studies — one based on findings at Axel Heiberg Island, near Ellesmere — pointing to increased mercury content in the environment and deadly ocean acidification as significant contributors to the extinction event.
And in November, Henderson co-authored a paper in the journal Science that clearly linked the Great Dying to a "runaway greenhouse event" triggered by the Siberian volcanoes at a time when the Earth's continents were still configured in a single landmass known as Pangea.
What the new evidence from Canada shows is that primitive sponges disappeared from the Ellesmere Island fossil record as early as 100,000 years before other known extinctions of species resulted from the volcanic eruptions.
"We're not sure how long the greenhouse effect lasted, but it seems to have been tens or hundreds of thousands of years," said University of Cincinnati geologist Thomas Algeo, a co-author of the GSA Bulletin study, in the research summary.
Extinction evidence from China and other parts of the world suggested that the mass die-off "was generally abrupt," Algeo stated. "Based on such observations, it has been widely inferred that the extinction was a globally synchronous event."
But the Canadian data shows the effects of the Siberian eruptions varied between locales depending on proximity to the epicentre of emissions, the depth of ocean water and other factors, with extinctions taking place over a long period of time.