Quebec island offers insight into mass extinction

Canada’s historic Anticosti Island has produced the first clear evidence that the planet’s second-largest mass extinction – the sudden disappearance of 75 per cent of all marine species on Earth about 450 million years ago – was caused by a rapid, five-degree plunge in ocean temperatures.

The discovery on the large Quebec island was reported just days after another team of scientists pointed to ash deposits on Axel Heiberg Island in the Canadian Arctic as proof that the planet’s biggest extinction event – when 95 per cent of all life died out 250 million years ago – was linked to volcano-fed coal fires in ancient Siberia.

Anticosti Island, located in the Gulf of St. Lawrence and first described by French explorer Jacques Cartier during his 1534 voyage of discovery to inland Canada, is widely viewed as a geological treasure. The steep cliffs along the island’s shores preserve a fossil-rich record of Earth history from a time when present-day North America was situated around the equator.

Scientists have long known that the so-called "Ordovician extinction" that killed off much of the world’s marine life 450 million years ago was somehow connected to an ice age that sharply reduced global sea levels, destroyed many coastal habitats and chilled ocean ecosystems.

But "exactly what caused this tremendous loss in biodiversity" – in other words, the precise mechanism of extinction – "remains a mystery," a team of nine U.S. researchers stated in a summary of their study, published in the latest issue of the journal Science.

So the team probed Anticosti’s unmatched record of fossilized marine creatures to produce the first detailed record of average Ordovician ocean temperatures.

Using the alignment of telltale molecules in the animals’ preserved shells as a "paleo-thermometer," the scientists discovered that a spike in extinctions during the Ordovician era coincided exactly with the sudden cooling of the seas.

"Our study strengthens the case for a direct link between climate change and extinction," California Institute of Technology researcher Seth Finnegan said in the study overview.

"Although polar glaciers existed for several million years, they only caused cooling of the tropical oceans during the short interval that coincides with the main pulse of mass extinction."

Study co-author Woodward Fischer, also a Caltech researcher, noted that "our observations imply a climate system distinct from anything we know about over the last 100 million years."

Finnegan told Postmedia News that Anticosti Island, which is 225 kilometres long and larger in area than Prince Edward Island, is a "fantastic place to do geology" because it is "one of the very few places that preserves a more or less complete sedimentary record" of rock layers from the Ordovician era.

"Thanks to the spectacular sea cliffs and river canyons," Finnegan added, "the exposures of these rocks are excellent, allowing us to sample them much more completely than we could in many other places."