The Mount Pinatubo eruption in 1991. (ARLAN NAEG/AFP/Getty Images)

On June 12, 1991, a mammoth cloud of ash and gas rose above Mount Pinatubo 55 miles north of Manila, the capital of the Philippines. Three days later, the volcano erupted, spewing millions of tons of smoke and gas — sulfur dioxide — into the atmosphere.

Though fairly insignificant in the sweep of geological history, it was the second-largest volcanic eruption of the 20th century. And what happened over the next few years may offer a vital clue to the world’s first mass extinction.

The average temperature worldwide decreased by a few tenths of a degree. “If relatively small eruptions like Pinatubo can affect the climate,” said Australian researcher Fred Jourdan of Curtin University, “just imagine what a volcanic province with an area equivalent to the size of the state of Western Australia can do.”

That’s exactly the objective of a new study published in Geology that claims to have found the cause behind one of world’s oldest mysteries: What caused the Cambrian extinction 500 million years ago?

There has long been general consensus that climate change and a depletion of oxygen in the oceans killed off more than 50 percent of the world’s species — but no one had known what had triggered those changes. Jourdan said massive volcano explosions in Western Australia, which lacquered more than 2 million square kilometers with lava, was the catalyst.

Schematic map of remnant of Kalkarindji large igneous province (LIP) in Australia. Ages (in Ma) from this study are shown in bold; those from Glass and Phillips (2006), Evins et al.(2009), and Macdonald et al. (2005) are in normal text. Age in italics indicates a young alteration event not related to the formation of the LIP. Proterozoic basins are indicated. Blackfella Rockhole Member volcanic breccia of Kalkarindji LIP is superimposed (orange) on Antrim basalts. Dashed line indicates likely original extent of LIP. (Courtesy of Fred Jourdan/ Curtin University Department of Applied Geology)

“This was the very first [study] to look at this, and the reason of the extinction was unknown until now,” Jourdan told The Washington Post in a phone interview. “It changed the global climate. It changed also the temperature and the chemistry of the ocean. This was the first extinction of complex life.”

Volcanoes caused other extinctions as well. At the end of the Triassic period, a massive volcanic explosion big enough to cover the United States in 300 feet of lava triggered an extinction that consumed 50 percent of life on Earth.

Another extinction was the Great Dying, which may have been caused by a microbe.  In a geologic “blink of an eye” — 60,000 years — it claimed more than 95 percent of the planet’s life, then mostly vertebrates and invertebrates.

Those extinctions were easier to study than the Earth’s first, which occurred 500 million years ago, and wiped out many trilobites, that era’s dominant species. “This extinction is very poorly studied because the rocks are so old,” Jourdan said. “When you look at rocks that are a billion years old, there’s so much decay and you don’t have traces of certain things anymore.”

Even with time hindering the analysis, Jourdan says he and his team of 10 researchers used radioactive dating techniques to discern that volcanic rock from the Kalkarindji volcanic province occurred at the same time as the first extinction.

For Jourdan, the findings weren’t much of a surprise. “I had suspected something like this and was testing a theory,” he said. “There had been a connection before with volcanic activity and a mass extinction.”

So how does a volcanic explosion wreck an entire planet? The answer: smoke and gas. Take Mount Pinatubo, Jourdan said. If such a small eruption can lower the Earth’s temperature, just imagine a truly massive explosion.

The study states it would result in “rapid climate changes and climate oscillations.”

Translation, Jourdan said: “Game over.”

“It was a yo-yo effect,” Jourdan says. “You had a long-term warming with the greenhouse gasses, but also a back-and-forth between warming and a cooling.”

One remaining mystery, however, is how long it took for species to die. Was it in a “blink of an eye” like the Great Dying? Or a slow-burn extinction?

Jourdan doesn’t know: “The rocks are just too old.”