News•March 21, 2013

Ancient Extinction Has Ominous Lessons for Today: Study

Scientists have nailed down the cause of a planet-wide catastrophe that wiped out nearly all living species 200 million years ago and paved the way for the rise of the dinosaurs. The culprit was carbon dioxide, the same greenhouse gas that’s causing global warming today says a new report.

The new study, which was published Thursday in the journal Science, said that unlike the current spate of warming, the gases that triggered the so-called End-Triassic Extinction (ETE) event came from an enormous series of volcanic eruptions, not from the burning of fossil fuels.

A study in the journal Science said that unlike the current spate of warming, the gases that triggered the so-called End-Triassic Extinction (ETE) event came from an enormous series of volcanic eruptions.
Credit: flickr/Óli Jón

Nevertheless, the result — a rapid rise in global temperatures and a change in ocean chemistry making seawater more acidic — is in many ways similar to what’s happening today, said Terrence Blackburn of the Carnegie Institution of Washington, who along with several colleagues authored the report.

“There’s a lot to be learned about how climate, life and the oceans respond to CO2,” Blackburn said in an interview.

To put it simply, things didn’t go well for vast numbers of plants and animals. No one knows the details of how many species perished, but it’s almost certainly the case that organisms that had evolved to thrive in conditions that existed just prior to the ETE couldn’t cope with changes in temperature, weather patterns and ocean chemistry that came with the massive spike in CO2 — the same general kinds of changes climate scientists believe are underway once again.

Scientists had long suspected that a gigantic series of volcanic eruptions triggered by the breakup of the world’s single continent, Pangaea, was the cause of the ETE, but while the eruptions and the extinctions broadly coincided, the timing of the former wasn’t known with enough precision to qualify it as a smoking gun. Indeed, some geologists had argued that the eruptions actually came after the extinction.

To nail down the timing more precisely, Blackburn and his colleagues collected zircon crystals from some of the 2.5 million cubic miles of cooled lava spewed out of those ancient volcanoes — including samples from the Palisades, a line of cliffs that residents of Manhattan’s Upper West Side can easily see from across the Hudson River.

Scientists had long suspected that a gigantic series of volcanic eruptions triggered by the breakup of the world’s single continent, Pangaea.
Credit: flickr/Narisa

Inside those crystals, the scientists were able to find samples of uranium that had partly decayed into lead. The relative amounts of those two elements allowed them to calculate how long the decay process had been going on, and thus when the eruptions happened. There were four separate pulses of volcanism, it turns out, spread out over some 600,000 years. But one powerful pulse came at 201 million years before the present, which puts the eruption at more or less exactly the same time as the extinction event.

Precisely how much CO2 would have entered the atmosphere is unknown. “There’s still some debate,” Blackburn said. “Some say the atmospheric concentration doubled, some say it tripled.”

Whatever the amount, the devastating effects on life are clear from the fossil record. For the dinosaurs, of course, the End-Triassic Extinction was a blessing, giving them a clear evolutionary playing field on which to flourish. The world was all theirs for the next 135 million years or so, until an asteroid slammed into Earth about 65 million years ago, causing the fifth mass extinction in the planet’s history and giving mammals a chance to take over.

Today, thanks to greenhouse gases from the burning of fossil fuels; deforestation and other changes wrought by human activity, biologists believe a sixth great extinction is under way. This time, there isn’t a volcano or asteroid to blame.