This article originally appeared on VICE US.
Life on Earth has diversified into countless forms over the course of billions of years, but it hasn’t always been a smooth ride. At least five major mass extinctions have occurred within the past 450 million years, each of which wiped out at least two-thirds of all species on the planet and left permanent marks in the geological and fossil records.
Now, a team of scientists propose adding a sixth major mass extinction: The end-Guadalupian event, also known as the end-Capitanian event, which occurred 260 million years ago.
This mass die-off is “in the same category with the other major mass extinctions,” according to a new paper in the journal Historical Biology that outlined the findings of several studies into the end-Guadalupian, and countered recent research that downplays the severity of the event.
At least half of marine life on the planet perished during the period, according to the researchers, as did a diverse group of land animals called dinocephalians. These animals were so dominant that their fossils can be found everywhere from Brazil to China to South Africa.
“There were big species losses in reef environments in the tropics, shallow bottom communities, and swimming organisms like coiled ammonoids,” said co-author Michael Rampino, an Earth scientist at New York University, in an email.
“The tropical marine organisms would have been hit hard by extreme warming and surface-ocean acidification from the massive volcanic release of carbon dioxide, similar to conditions developing today,” he added.
Rampino and co-author Shu-zhong Shen, an Earth scientist at Nanjing University, built on several studies linking the end-Guadalupian event to major volcanic activity that persisted for more than a million years.
The event created the Emeishan Traps, a massive basaltic formation that stretches across southwest China. For years, scientists have debated whether these eruptions caused extinctions limited to that region, or on a global scale. The new study summarized field work showing that the volcanic activity triggered sudden climate change that destabilized ecosystems around the planet.
Rampino and Shen are not the only scientists who have suggested that this event be recognized as a mass extinction by the scientific community. In 2015, two teams made similar recommendations in unrelated studies published in the Proceedings of the Royal Society B and the Geological Society of America Bulletin.
Despite these efforts, the end-Guadalupian event has continued to be overlooked as a sixth mass extinction event (this tally does not count the Anthropocene, a proposed new event caused by human activity, which is also sometimes referred to as the sixth mass extinction. If the end-Guadalupian event is accepted, a contemporary extinction event would be the seventh).
The end-Guadalupian event has been side-stepped in part because it was rapidly followed by the mother of all mass extinctions—the Permian-Triassic event, also known as the Great Dying.
Just eight million years after the end-Guadalupian die-off, intense volcanic eruptions pulverized what is now Siberia, creating the vast Siberian Traps formation. These eruptions lasted for two million years and were the catalyst for the Great Dying, which is by far the most severe known extinction event. Some 70 percent of terrestrial vertebrates and 96% of all marine life were wiped off the face of the planet.
It’s been hard, until now, for the end-Guadalupian to stand out in comparison to this mind-boggling loss of global life. “It was difficult to separate the end-Guadalupian event from the end-Permian event only eight million years later,” Rampino said. “Recent paleontological research has clearly separated the two, and shows the severity of the end-Guadalupian event.”
Rampino and Shen are the latest in a growing group of scientists who argue that the preceding event was on the same scale as other mass extinctions, though admittedly nowhere near as rough as the Great Dying.
“In terms of both losses in the number of species and overall ecological damage, the end-Guadalupian event now ranks as a major mass extinction, similar to the other five,” the team concluded in the study.