Discovering the Cause of the First Mass Extinction in the Limestone Strata of Anticosti Island

In his laboratory, Professor André Desrochers is sitting in front of a tray of blue-capped vials. With his left hand, he is removing one of the vials from the tray.

Professor André Desrochers (University of Ottawa) with Professor Maya Elrick (University of New Mexico), Rick Bartlett (Elrick’s former MSc student, now at Louisiana State University), and Professor James Wheeley (University of Birmingham, England)

Department of Earth and Environmental Sciences

The vast record of fossils preserved in the limestone strata of Anticosti Island, located at the mouth of the Gulf of St. Lawrence, has revealed the cause of the first mass extinction of animal life on Earth. Throughout the planet’s history, there have been five mass extinctions, the causes of which include massive volcanic eruptions, global warming, asteroid collisions and oceanic acidification. However, the events that triggered the first mass extinction of marine life, which took place around 444 million years ago, a time known as the late Ordovician period, have remained a mystery until recently. When this first mass extinction took place, most of what is now North America was covered in shallow tropical seas, home to abundant life forms such as corals, bryozoans, brachiopods, and crinoids. However, the large ice sheets that developed far away from Anticosti Island deeply affected the way sediments were deposited in these shallow seas, which in turn had a major impact on these environments, critically affecting the marine life living in them and contributing to the Late Ordovician Mass Extinction. Anticosti Island is where Professor André Desrochers and his international colleagues have discovered geochemical proof in the limestone strata that suggests that this extinction was caused by a sustained period of decreased oxygen in the oceans, a condition known as marine anoxia. This event caused the death of 85% of marine life through asphyxiation.

Major discoveries such as this one have put Anticosti Island in the running to be recognized as a World Heritage Site by the United Nations Educational, Scientific, and Cultural Organization (UNESCO).

Read the full abstract in the Proceedings of the National Academy of Sciences

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