(CN) — Dinosaurs were decimated 66 million years ago after a huge asteroid slammed into the Earth and temperatures plunged worldwide as dust blotted out the sun. Yet dinosaurs had come to dominate the globe thanks to an earlier volcano-induced extinction event, scientists say in a new study.
Some 234 to 232 million years ago, in what today is the Wrangellia region of western Canada, volcanoes spewed lava that cooled into tons of basalt, and pumped so many greenhouse gases into the atmosphere it caused global warming, raising temperatures 7.2 degrees Fahrenheit, according to a team of 17 researchers.
The higher temperatures accelerated evaporation, causing a period of high humidity and increased rainfall that lasted for 1 million years.
Analyzing fossils found in Europe, South America, China and British Columbia, the scientists said this event caused the disappearance of numerous marine and terrestrial species. Rhynchosaurs, plant-eating lizards with clawed hindfeet, whose fossils are found around the globe, are one of the species that died off.
“The climate change caused major biodiversity loss in the ocean and on land, but 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 modern conifer forests,” the researchers said in a statement.
Though dinosaurs originated 20 million years before this event, which scientists call the Carnian Pluvial Episode, they did not flourish until the arrival of arid conditions that marked the end of the episode.
“It wasn't just dinosaurs, but also 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 team said.
They laid out their work in a report published Wednesday in the online journal Science Advances.
The report contains highly technical data – anyone up for a “negative carbon isotope excursion”? – difficult for the layman to understand.
Lead researcher Mike Benton, a paleontology professor at the University of Bristol, was asked how he would describe the importance of the findings to a 10-year-old.
“We all know the dinosaurs were wiped out by a huge mass extinction,” he said, “when an asteroid hit the Earth and climates went through major shock changes. But the dinosaurs got their chance much earlier following another mass extinction.”
He added, “This time they were not victims but benefited - earlier groups of plant-eating reptiles in particular could not cope with the sudden climate changes and changes in plants, and dinosaurs, which had been around for some time but very rare, took off into the new, empty space.”
The Carnian Pluvial Episode was also a boon for coral reefs.
“Reef communities underwent a renaissance,” the report states.
Benton said coral reefs, which are made of limestone skeletons secreted by coral polyps, shifted from shallow water continental shelves to the deep oceans. The shift enhanced the ocean’s ability to absorb carbon dioxide, thus helping stabilize the atmosphere.
Jacopo Dal Corso, of the China University of Geosciences at Wuhan, also led the research. He said paleontologists had identified five large mass extinctions in the past 500 million years.
"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,” Dal Corso said in a statement.
Inklings of this event were discovered in the 1980s, Benton said, but radioisotopic dating, a method of figuring out the age of rocks, was not yet advanced enough to link sedimentary rocks to volcanic activity in the Wrangellia area.
In an email, Benton said field work in South America and China was key to showing this was a global event.
Despite the advances, the study team says better radioisotopic dating is needed to pin down how long the Carnian Pluvial Episode lasted, and the rates at which the volcanoes spewed magma and released greenhouse gases.
“Integrating detailed stratigraphic, geochemical, and radioisotope data will clarify the sequence of events and possible cause-and-effect relationships,” the report concludes, “so helping in understanding this unique interval in Earth history and the intimate causes of the extinction and, maybe most crucially, the unique diversification event that led to the formation of modern ecosystems.”
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