Changes to the oceans, as extreme volcanic activity made them more acidic, triggered the greatest mass extinctions of all time, according to a study.
The event, which took place 252 million years ago, happened when the oceans became more acidic due to absorbing huge amounts of carbon dioxide from volcanic eruptions.
The study is the first to show that highly acidic oceans were to blame.
The findings are helping scientists understand the threat posed to marine life by modern ocean acidification.
The amount of carbon added to the atmosphere which triggered the mass extinction was probably greater than today’s fossil fuel reserves, the researchers say.
However, the carbon was released at a rate similar to modern emissions. This fast rate of release was a critical factor driving ocean acidification.
The Permian-Triassic Boundary extinction took place over a 60,000 year period, researchers say. Acidification of the oceans lasted for 10,000 years.
The team analysed rocks unearthed in the United Arab Emirates – which were on the ocean floor at the time – to develop a climate model to work out what drove the extinction. The rocks preserve a detailed record of changing oceanic conditions at the time.
Dr Matthew Clarkson, of the University of Edinburgh’s School of GeoSciences said: “Scientists have long suspected that an ocean acidification event occurred during the greatest mass extinction of all time, but direct evidence has been lacking until now. This is a worrying finding, considering that we can already see an increase in ocean acidity today that is the result of human carbon emissions.”