Earth's worst mass extinction event was 'The 'Great Dying' some 252 million years ago – long before the asteroid that killed the dinosaurs.
It was the most severe extinction event of the past 500 million years, wiping out 80% to 90% of species on land and in the sea.
Now scientists have analysed minerals in southern China, which indicate that eruptions produced a "volcanic winter" that drastically lowered Earth's temperature, before a period of violent global warming.
Michael Rampino, a professor at New York University’s department of biology, said: "As we look closer at the geologic record at the time of the great extinction, we are finding that the end-Permian global environmental disaster may have had multiple causes among marine and non-marine species."
For decades, scientists have investigated what could have caused this global ecological catastrophe, with many pointing to the spread of vast floods of lava across what is known as the Siberian Traps, a large region of volcanic rock in the Russian province of Siberia.
These eruptions caused severe global warming from volcanic releases of carbon dioxide and related reduction in oxygenation of ocean waters that caused ocean life to suffocate.
The team considered other factors that may have contributed to the end of the Permian Period, which stretched from 300 million to 250 million years ago.
They found mineral and related deposits on land in the south China region – copper and mercury – whose age coincided with the end-Permian mass extinction.
These deposits were marked by anomalies in their composition that were probably due to sulphur-rich emissions from nearby volcanic eruptions.
Rampino said: "Sulphuric acid atmospheric aerosols produced by the eruptions may have been the cause of rapid global cooling of several degrees, prior to the severe warming seen across the end-Permian mass-extinction interval."
The environmental effects of the eruptions in south China, and elsewhere, may have played a vital role in the disappearance of dozens of species, Rampino said.
Recent research showed that extinction did not come at the same speed, and that the process took far longer on land after many species in the seas had already died.
The research could have important implications for our present-day battle against climate change, the researchers have warned.
Pia Viglietti, a postdoctoral researcher at Chicago's Field Museum, said: "People assumed that because the marine extinction happened over a short period of time, life on land should have followed the same pattern, but we found that the marine extinction may actually be a punctuation to a longer, more drawn-out event on land."
Viglietti, Angielczyk and their colleagues examined fossils from 588 four-legged fossil animals that lived in what's now South Africa's Karoo Basin at the time of the Permian mass extinction.
They created a database and separated the fossils by age, grouping together specimens by 300,000-year time intervals, allowing the researchers to quantify the appearance and disappearance of different species and look at the bigger picture of life over time.
Viglietti said: "Our approach unifies the data and says, OK, within this time bin we have these species, but as we go up, we have these other species.
"By applying sampling methods to these bins, we can help correct for issues like having more or fewer specimens collected in different time intervals or places. Ultimately, it lets us quantify how much extinction is happening and how quickly new species are appearing.
"Instead of putting too much focus on any one fossil, you compile hundreds of observations roughly in the same time interval."
The fossils showed the researchers that the Permian extinction looked very different on land than it did in the oceans, where it lasted a mere 100,000 years.
The extinctions on land took 10 times as long.