Rock samples in Quebec offer clues into the cause of Earth's first mass extinction event

Rock samples from Quebec's Anticosti Island are offering new clues about Earth's first major mass extinction event 445 million years ago, suggesting that it may have been caused by a cooling climate.

A team of scientists from the U.S., China, France and the University of Ottawa published a paper in the journal Nature Geoscience exploring the Late Ordovician mass extinction event, which took place around 445 million years ago. It is the oldest among the "big five" mass extinction events and saw around 85 per cent of marine species disappear during that time.

“If you had gone snorkeling in an Ordovician sea you would have seen some familiar groups like clams and snails and sponges, but also many other groups that are now very reduced in diversity or entirely extinct like trilobites, brachiopods and crinoids,” said study co-author Seth Finnegan in a news release.

But when these species disappeared, they didn't die off suddenly, like how the dinosaurs did during the Cretaceous extinction 65 million years ago. Instead, the Late Ordovician mass extinction event played over a period of 500,000 to two million years.

The researchers sought to investigate whether a lack of oxygen in the seawater, also known as anoxia, played a part in the mass extinction. Anoxia and global cooling are two of the prevailing hypotheses on the cause of the extinction event.