Not the volcano responsible. Image: Wikimedia Commons
The climate changes, the ocean follows suit, and the extinctions follow. That's the shape of both Earth's latest era of mass extinction, as well as its first. However, in the latter's case, the cause of the changing climate and seas has been revealed to be ancient volcanoes erupting in what is now Western Australia.
Fred Jourdan, a geology professor at Curtin University in Perth, Australia, led a research team that measured the age of the eruptions of the Kalkarindji volcanic province, where lava flows covered over 2 million square kilometers. In results published in the journal Geology, the team found that the eruptions coincided with the Early-Middle Cambrian extinction some 511 million years ago.
“We calculated a near perfect chronological correlation between large volcanic province eruptions, climate shifts and mass extinctions over the history of life during the last 550 million years, with only one chance over 20 billion that this correlation is just a coincidence,” Jourdan said in a statement.
The dashed line indicates the borders of the Kalkarindji "large igneous province." Image: Fred Jourdan/ Curtin University Department of Applied Geology
“Not only were we able to demonstrate that the Kalkarindji volcanic province was emplaced at the exact same time as the Cambrian extinction, but were also able to measure a depletion of sulfur dioxide from the province’s volcanic rocks—which indicates sulfur was released into the atmosphere during the eruptions,” he said.
The addition of large quantities of sulfur to the atmosphere can affect global temperatures for a long time and in dramatic ways. Sulfate aerosols remain in the atmosphere after volcanic eruptions, and are thought to cause surface cooling by reflecting energy from the Sun back into space.
Sulfate aerosols from the massive eruption of Indonesia's Mount Tambora in 1815 are thought to be at least one cause behind the "year without a summer" that followed, which killed crops in North America and caused famine in Europe. But there are more recent example of this phenomenon as well.
“As a modern comparison, when the small volcano Pinatubo erupted in 1991, the resulting discharge of sulphur dioxide decreased the average global temperatures by a few tenths of a degree for a few years following the eruption,” Jourdan said. “If relatively small eruptions like Pinatubo can affect the climate just imagine what a volcanic province with an area equivalent to the size of the state of Western Australia can do.”
Turns out, it could do quite a bit. While not considered one of the “big five” mass extinction events, the Early-Middle Cambrian extinction was, nevertheless, a doozy. It was the first extinction that wiped out complex multicellular life, Jourdan said, in the course of eradicating 50 percent of species on Earth. The eruptions released methane and carbon dioxide into the atmosphere along with the sulphur, leading to rapid oscillations of the climate. The changes depleted the amount of oxygen in the oceans, where most of life then lived, too quickly for most species to adapt. Many species of trilobite didn't make it through.
“It was a yo-yo effect,” Jourdan told the Washington Post. “You had a long-term warming with the greenhouse gasses, but also a back-and-forth between warming and a cooling.”
Last week researchers came forward to point out that we people are probably causing the sixth mass extinction event in Earth's history—which strikes me, as a human, as just a stone cold bummer to consider. So it's sort of comforting to think back on the mass extinctions that we didn't cause, every now and then. Okay, maybe comforting isn't the right word.