The asteroid strike that doomed the dinosaurs is an event that many people are aware of. It wiped out more than three-quarters of all life on Earth 66 million years ago.
But it was only one of the Big Five mass extinctions the planet has experienced since living organisms evolved 3.5 billion years ago, and wasn’t the worst.
Now, scientists say they have identified evidence of a new mass extinction event in the fossil record, and it’s one that allowed dinosaurs to dominate the Earth for more than 200 million years.
It took place 232 million to 234 million years ago and has been called the Carnian Pluvial Episode.
“So far, palaeontologists had identified five ‘big’ mass extinctions in the past 500 million years of the history of life,” said study co-author Jacopo Dal Corso, a geologist at China University of Geosciences at Wuhan, in a news statement.
“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.”
The cause, the researchers said, was most likely massive volcanic eruptions in what is now western Canada, where huge volumes of volcanic basalt was poured out and ultimately formed much of the western coast of North America.
“The eruptions were so huge, they pumped vast amounts of greenhouse gases like carbon dioxide, and there were spikes of global warming,” Dal Corso said.
The change in the climate caused major biodiversity loss in the ocean and on land. Just after the extinction event new groups took over, forming more modern-like ecosystems. The shifts in climate encouraged growth of plant life, and the expansion of conifer forests – the largely evergreen trees we know today with needles and cones.
It wasn’t just dinosaurs. Many modern groups of plants and animals also appeared at this time, including some of the first turtles, crocodiles, lizards and the first mammals.
The Carnian Pluvial Episode also had an impact on ocean life, with 33% of marine life disappearing, according to the study, which published in the journal Scientific Advances. It marked the start of the type of coral reefs seen today, as well as many of the modern groups of plankton, suggesting profound changes in the ocean chemistry after the mass extinction event.
The warming climate was also associated with increased rainfall, and this had been detected back in the 1980s as a humid episode lasting about 1 million years in all. But it was “the sudden arid conditions after the humid episode that gave dinosaurs their chance,” said study co-author Mike Benton, professor of vertebrate paleontology at the University of Bristol in the United Kingdom in the 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,” Benton said.
Alfio Alessandro Chiarenza, a paleontologist and research associate at University College London, said while the study highlighted many of the important changes that life underwent during this time frame, he was “cautious in defining this as a mass extinction.”
“Given the unevenness of the fossil record, our information on biodiversity trends through time and space are oftentimes patchy,” he said via email.
“Fossils may be ‘hiding’ in rocks we still haven’t investigated or simply didn’t get preserved to our days,” he added.
Scientists typically define a mass extinction as the disappearance of at least 50% of all species over a short space of time. Geologically speaking, that time period is usually less than 2.8 million years.
Benton told CNN they couldn’t yet estimate a figure for the loss of terrestrial life, but the event would have affected plants and animals of widely different ecologies across the globe and with substantial species loss in a short time span.
The worst mass extinction event happened 250 million years ago, wiping out 95% of all species and was likely because of massive volcanic eruptions in Siberia.
Some researchers believe we are currently experiencing another mass extinction event – but one that is largely our fault.