Mass extinction events leave an enormous footprint in their wake, transforming the landscape of the planet as swathes of new species swoop in to replace those who perished as a result of the change. Because of this, they’re not something you come across very often as most stand out pretty clearly in the fossil record.
However, a new study published in the journal Science Advances has revealed a previously unknown mass extinction event that occurred 233 million years ago and brought in the age of dinosaurs. Named the Carnian Pluvial Episode, the event is thought to have most likely been driven by volcanic eruptions in the Wrangellia Province of western Canada, churning out plumes of volcanic basalt that spilled out to form what we now know as the western coast of North America.
It resulted in an enormous loss of life, pushing scores of plant and animal life to extinction. The study authors explain that what plant life survived likely proved slim pickings for the herbivorous reptiles that survived, spelling their demise and clearing the way for new species.
"I had noted a floral switch and ecological catastrophe among the herbivores back in 1983 when I completed my PhD,” said one of the lead authors Mike Benton, of the University of Bristol's School of Earth Sciences, in a statement. “We now know that dinosaurs originated some 20 million years before this event, but they remained quite rare and unimportant until the Carnian Pluvial Episode hit. It was the sudden arid conditions after the humid episode that gave dinosaurs their chance."
So how do you stumble across a mass extinction event? The discovery was made by a team of 17 researchers, co-led by Jacopo Dal Corso of the China University of Geosciences at Wuhan, who reviewed extensive records of the geological and palaeontological evidence from this time period. Combined with existing research into geochemical signatures that indicate the prevalence of volcanic eruptions, as well as looking for signs of increased rainfall, they were able to piece together an ancient puzzle that revealed how dinosaurs came to dominate the Earth.
"I was studying the geochemical signature of the eruptions a few years ago and identified some massive effects on the atmosphere worldwide,” said Dal Corso. “The eruptions were so huge, they pumped vast amounts of greenhouse gases like carbon dioxide, and there were spikes of global warming.”
The warming and increased rainfall over a period of 1 million years triggered major biodiversity loss both on land and in the ocean, leaving plenty of empty niches for new groups to take over. And it wasn’t just dinosaurs who stepped up to the plate, as lots of modern groups of plants and animals made their debut, including some of the first turtles, crocodiles, lizards, and the first mammals.
"So far, palaeontologists had identified five 'big' mass extinctions in the past 500 million years of the history of life," said Dal Corso. "Each of these had a profound effect on the evolution of the Earth and of life. We have identified another great extinction event, and it evidently had a major role in helping to reset life on land and in the oceans, marking the origins of modern ecosystems."