It's a hot, sunny day at the equator. Standing at the edge of a great salt lake, you look out across its shimmering beauty; waves lap delicately at your feet. Far in the distance mirages weld its shores — salt flats — to an unbroken blue sky.
If a new theory is right, you are standing at ground zero of the greatest apocalypse the world has ever seen.
During the end-Permian mass extinction 250 million years ago, nearly 90 percent of life on Earth was extinguished, and everything from magnetic field reversals to supervolcanoes has been invoked to explain it. But a group of researchers have an even more provocative idea for the murder weapon: poisonous gases vented from dried-up salt lakes.
Their case begins with a lagoon off the Caspian Sea in Turkmenistan. Spanning 7,000 square miles, the Kara-Bogaz-Gol bay is constantly evaporating in a delicate balance with waters from the Caspian. It harbors a huge amount of salt and also emits a stream of toxic gases into the atmosphere.
Ludwig Weissflog of the UFZ-Helmholtz Center for Environmental Research in Germany and a team of researchers measured gases coming from the Kara-Bogaz-Gol. They found large amounts of halogenated hydrocarbons (HHCs), chemicals like chloroform and trichloroethylene that are known to be poisonous and corrosive to Earth's ozone layer.
Once they get into the atmosphere, the chemicals can also kill plants. Co-author Kastern Kotte of the Max Planck Institute for Chemistry said that during the end-Permian, conditions were hot and arid enough that there may have been a huge number of drying salt lakes on Earth, including Lake Zechstein, which was the size of Texas and covered much of what is now western Europe.
With enough gas, plants would've died en masse. The lack of food and oxygen from decreased photosynthesis would cascade through the food chain, killing land animals and even spilling into the sea.
Kotte admits the team's argument is still circumstantial, based on a just few laboratory measurements of emissions from the Kara-Bogaz-Gol's salt deposits. "Right now we are not sure what the emissions budget for the salt pans would be worldwide," he says. "We hope to know more within a year or two."
"Yes, we know of major evaporative seas in the late Permian," said Jonathan Payne of Stanford University. "But can we look at the rest of the Phanerozoic and say that there was far more evaporation during this extinction than at other times? That's a major question."
Payne acknowledged that lake-borne poisonous gases may have indeed played a role in the extinction, but said it's unlikely they could've done such a thorough job of killing on their own.
"The HHCs are undoubtedly bad for biology, but that probably can't explain all of the global extinction effects we see," he said. "You need the carbon dioxide and other gases from the massive eruption of the Siberian Traps, too."
