April 3, 2009 A new report by an international team of scientists has suggested that the largest mass extinction in the history of the earth may not have been caused by volcanic eruptions, methane hydrate or the impact of an asteroid as previously surmised. It may actually have been triggered by giant salt lakes, whose emissions of halogenated gases changed the atmospheric composition to such an extent that vegetation was irretrievably damaged. While this is a lot less dramatic than a volcanic eruption or an asteroid, the effect would be no less devastating and may have implications for us today with forecasts predicting an increase in the surface areas of deserts and salt lakes due to climate change that researchers expect will also lead to an increase in the effects of these halogenated gases.

The team of researchers from Russia, Austria, South Africa and Germany discovered that microbial processes in present-day salt lakes in the south of Russia and South Africa naturally produce and emit highly volatile halocarbons such as chloroform, trichloroethene, and tetrachloroethene. They transcribed these findings to the Zechstein Sea, which about 250 million years ago in the Permian Age, was situated about where present day Central Europe is. With a total surface area of around 600,000 km2 the Zechstein Sea was almost as large as France is today. The hyper saline flat sea at that time was exposed to a predominantly dry continental desert climate and intensive solar radiation - like today’s salt seas – allowing the team to conclude that the climatic, geo-chemical and microbial conditions in the area of the Zechstein Sea were comparable with those of the present day salt seas that they investigated.

Based on comparable calculations from halogenated gas emissions in the atmosphere from present-day salt seas in the south of Russia, the scientists calculated that from the Zechstein Sea alone an annual VHC emissions rate of at least 1.3 million tonnes of trichloroethene, 1.3 million tonnes of tetrachloroethene, 1.1 million tonnes of chloroform as well as 0.050 million tonnes of methyl chloroform can be assumed. By comparison, the annual global industrial emissions of trichloroethene and tetrachloroethene amount to only about 20 percent of that respectively, and only about 5 percent of the chloroform from the emissions calculated for the Zechstein Sea by the scientists. Incidentally, the industrial production of methyl chloroform, which depletes the ozone layer, has been banned since 1987 by regulation of the Montreal Protocol.

The team then used steppe plant species to prove that halogenated gases contribute to speeding up desertification as the combination of stress induced by dryness and the simultaneous chemical stressor `halogenated hydrocarbons´ disproportionately damages and destabilizes the plants and speeds up the process of erosion. Based on both of these findings the researchers were able to form their new hypothesis that at the end of the Permian Age the emissions of halogenated gases from the Zechstein Sea and other salt seas were responsible in a complex chain of events for the world’s largest mass extinction in the history of the earth, in which about 90 percent of the animal and plant species of that time became extinct.

What is really worrying though is that, aside from all its other wonderful effects, climate change could also see an increase in the effects of these halogenated gases. The International Panel on Climate Change (IPCC), predicts increasing temperatures and aridity will speed up desertification, increasing with it the number and surface area of salt seas, salt lagoons and salt marshlands, which will then lead to an increase in naturally formed halogenated gases. The phytotoxic effects of these substances become intensified in conjunction with other atmospheric pollutants and at the same time increase dryness and exponentially drive the eco-toxicological consequences of climate change.

While the new theory is just that, a theory, it could be like a jigsaw piece that contributes to solving the puzzle of the largest mass extinction in the history of the earth. Whether the halogenated gases from the giant salt lakes alone were responsible for it or whether it was a combination of various factors with volcanic eruptions, the impact of asteroids, or methane hydrate each playing a part remains unanswered, but the team is adamant that the effects of salt seas were previously underestimated. The team also hopes to show that the recent salt lakes and salt deserts of south-east Europe, Middle Asia, Australia, Africa and America can not only influence the regional but also the global climate. Their findings on the effects of these halogenated gases are therefore important for revising climate models, which form the basis for climate forecasts. And hey, you never know, these revised climate models might provide good news. Right? There’s a chance. Oh, who am I kidding - we’re screwed.

Darren Quick

View gallery - 2 images