This post has been updated.
About 260 million years ago, a vast volcanic region in China began to erupt, leaking lava and spewing plumes of hot gas and ash into the air. The eruption pumped carbon dioxide into the atmosphere, causing the global climate to rapidly heat up, and poisoned the oceans, turning them acidic and leaching oxygen from the water.
The effects on the inhabitants of that very ancient world (mostly clam-like creatures and single-celled organisms) were devastating, but it wasn’t clear exactly how devastating until recently, when a study in the Geological Society of America Bulletin offered evidence that the event was no ordinary population die-off. Instead, researchers believe it qualifies as a “mass extinction” on the order of the death of the dinosaurs nearly 200 million years later.
“It’s the first time we can say this is a global mass extinction,” lead author David Bond, a paleontologist at the University of Hull in Britain and researcher with the Natural Environment Research Council, said in a phone interview.
Paleontologists have known about this 260-million-year-old event since the mid-1990s, when they discovered fossil evidence of widespread extinctions in China during what’s called the Capitanian Age. But because the majority of die-offs were thought to have happened in the tropics, they have never considered it among the “Big Five” mass extinction events — an elite group of disasters when large swaths of the Earth’s species were wiped out in a short amount of time.
To test whether the eruption caused enough worldwide death and mayhem to qualify as a sixth, Bond and his colleagues headed far, far away from the tropics, to the icy Norwegian island of Spitsbergen just a few hundred miles from the North Pole. Toting research equipment and rifles (to ward off polar bears) they dug into a massive rock structure called the Kapp Starostin Formation. The formation, created by rock that gets deposited in strata over millions of years, forms distinct layers that scientists can use to date the fossils they find within it, like rings on a tree.
Bond said he didn’t mind the chilly working conditions.
“Its’ a great place to work, stunningly beautiful and remote,” he said. “You really feel like you’re out there exploring.”
Having obtained their samples, Bond’s team identified the rock layer that corresponded with 260-million-year-old die-offs found in the tropics and examined the fossil record preserved within it. Most of the Capitanian layer was filled with the skeletons of brachiopods, unimpressive clam-like species that flourished during that time. But at a certain point, the fossils vanish.
“It’s like a blackout zone and there’s nothing around,” co-author Paul Wignall, a paleontologist at the University of Leeds, told Science Magazine.
That blackout zone jibed with previously discovered fossil records from farther south, where other brachiopods and marine creatures were also wiped out. To the researchers, this demonstrated that the extinctions were happening worldwide, not just to one small population. Bond says that 87 percent of the brachiopod species vanished in that time, and perhaps 70 percent of all other species.
The culprit, he believes, was the Emeishan Traps — an area in southwestern China where huge amounts of liquid volcanic rock seep up from beneath Earth’s crust. The eruption of the traps released carbon dioxide into the atmosphere, which was then absorbed by oceans, turning them acidic. This created a toxic environment for the brachiopods and other critters, and they never fully recovered.
Instead, the remainder of the Capitanian period was dominated by bivalves, a physically similar but evolutionary unrelated species. Those animals flourished until a few million years later, when the Permian mass extinction — sometimes called “the Great Dying” — wiped out the bivalves and 96 percent of all other species.
The Capitanian extinction’s proximity (according to geological standards) to the Permian event is one of the reasons that other scientists remain skeptical of the “mass extinction” categorization. The death of the brachiopods could have merely been a preamble to the broader extinction that followed.
Matthew Clapham, a paleontologist at the University of California at Santa Cruz, also called the timing of the brachiopod deaths into question. It’s possible that the Norwegian brachiopods died a few million years later than their relatives in the tropics, he told Science.
“They’ve definitely identified a real event, which is really interesting,” he said, but he believes the Capitanian is probably 30th or 40th in the hierarchy of extinctions, not sixth.
Bond admits that his research needs refining, and he doesn’t mind the criticism — it’s an inevitable byproduct of working in the mass extinction field, which apparently is a veritable hotbed of scientific controversy.
“It’s a really fierce world, and people will argue probably forever about these things,” he said. “That’s what makes it interesting.”