|An artist's impression of the Siberian Flood Basalt Event|
A popular theory is that the Siberian Flood Basalt Event may have triggered the extinction. This is where a section of marine plate boundary, many thousands of miles in length, rises, releasing hundreds of millions tonnes of molten rock into the oceans. The Permian Flood Basalt Event produced so much lava that the entire bedrock of north Siberia, a geological province known as the Siberian Traps, is composed of the solidified remains of this huge event.
The molten rock would have raced across the sea bed, destroying thousands of square kilometres of reef systems. Yet the total impact of the event extends far beyond this. Its most deadly effect lies in the release of gases into the atmosphere. Apart from many different toxins present in the Earth's mantle, reactions between the calcium carbonate skeletons of the reef systems and the heat of the lava would have created hundreds of millions of tonnes of carbon dioxide.
Trapped pockets of methane would have also been opened. Methane is a greenhouse gas 50 times more effective at trapping heat than carbon dioxide. Hydrogen sulphide would have been produced as well. As Methane bubbled up through the oceans, it would have poisoned organisms at all levels, before damaging the ozone layer and trapping the sun's heat. These three gases alone would have wreaked havoc. Yet a team of geologists may have found yet more.
The halogens, such as bromine and iodine, are incredibly reactive. They form a vast range of compounds, some benign, others highly toxic, such as chlorofluorocarbons, another group of greenhouse gases which deplete the ozone layer along with hydrogen sulphide. The geologists, led by Benjamin Black from the Massachusetts Institute of Technology, studied samples of Siberian Trap Basalts, looking at the concentrations of sulphur, chlorine and fluorine.
Based upon their findings, the team estimate that 6,300 to 7,800 gigatonnes of sulphur were released into the atmosphere, alongside 3,400 to 8,700 gigatonnes of chlorine, and 7,100 to 13,700 gigatonnes of fluorine. A single gigatonne is comprised of one billion tonnes. These vast quantities of reactive gases released into the atmosphere, apart from causing catastrophic fluctuations in the global climate, would have caused millions of years of acid rain, ruining completely hundreds of ecosystems.
As if the original theories about the Great Dying were not enough, there is now the possibility of extreme problems with atmospheric chemistry as well as global warming, volcanic super-eruptions and worldwide poisoning of the oceans by hydrogen sulphide and millions of tonnes of mercury. Yet Black and his team say that more research on atmospheric chemistry and climate modeling is urgently needed to determine whether these gasses were responsible for the mass extinction.