Hyper-saline: The likely pink colour of the Zechstein Sea would have been brought about by microbes with an extreme preference for salt, as is the case with salt lakes today.
Credit: Karsten Kotte/Universität Heidelberg
"Extreme biological events attract extreme hypotheses to explain their occurrence, and the proposal that giant salt lakes triggered the largest mass extinction in Earth's history about 250 million years ago is an interesting addition to the list," said Squire.
But he argued that the Cambrian–Precambrian boundary, 542 million years ago, was another major salt-producing episode in Earth's history and that, instead of leading to a mass extinction, this period was characterised by a sudden and explosive radiation of animal life.
Mutation rate
"Why did one event coincide with the most explosive flourishing of complex life on Earth when a subsequent (and possibly smaller) event did the opposite?" said Squire.
But Weissflog countered that conditions were different at the Cambrian boundary, when most life was aquatic rather than land-based, and less prone to damage from atmospheric dryness. He added that at this time ozone depletion from halocarbons would have sped up mutation in DNA, leading to rapid evolution.
"The effects of UV-B radiation lead to an increasing of the mutation rate and so to an increase in biodiversity," he told Cosmos Online.
Accelerated mutations
Accelerated mutations can and do coincide with stressed populations due to inbreeding.