Climate Change - The End-Permian Mass Extinction
Five major mass extinction events are recorded in the rock record of the last 600 million years.
The biggest extinction was at the end of the Permian, around 252 million years ago.
Only about 8% of species survived to live on in the Triassic Period.
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The event played out over 60,000 years.
Acidification of the oceans lasted for about 10,000 years.
Two separate pulses of CO2 into the atmosphere - a "one-two punch" - may have been involved in the die-off, according to new research.
CO2 was released by massive volcanism from the Siberian Traps, now represented as a large region of volcanic rock.
A large amount of coal had been burned over a period of tens of thousands of years.
The coal was burned by the Siberian Traps volcanic activity.
The burning actually happened underground, with the carbon dioxide and ash mixing with magma.
This produced vast amounts of CO2 which warmed the Earth and changed the chemistry of the oceans.
The research team, led by Dr Matthew Clarkson from the University of Edinburgh, examined rocks in the United Arab Emirates. 
The rocks, which were on the ocean floor at the time, preserve a detailed record of changing oceanic conditions.
The carbon was released at a similar rate to modern emissions.
Dr Clarkson says "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."
