R. A. Wood United Arab Emirates: rocks indicate acidity that may have led to mass extinctionsR. A. Wood
A chemical analysis of limestone collected in the United Arab Emirates has provided the most compelling evidence to date that the largest mass extinction event in Earth’s history may have been caused by ocean acidification – the same process triggered by the excess carbon dioxide produced by humanity today. The event happened 250 million years ago, when 90% of all living species were wiped out, especially marine life. An international team of geologists, headed by Matthew Clarkson from the University of Otago, New Zealand, analyzed the amounts of boron isotopes and other elements in rocks formed from calcium carbonate precipitation on the sea floor during the extinction event (Science, April 10, 2015). The analysis concluded that within a period of five thousand years, dissolved carbon dioxide acidified the seawater to levels up to 10 times higher than normal. The source of the gas was volcanic activity in the existing land masses at the time, releasing trillions of tons of carbon into the atmosphere. Acidity is deadly to marine creatures that live in shells or exoskeletons because it hinders the absorption of calcium, the main component of these carapaces. One of the authors of the study, geologist Simone Kasemann from the University of Bremen, in Germany, works in collaboration with a team from the University of São Paulo that includes geologist Marly Babinski and her doctoral student Gustavo Paula-Santos. They are planning to use the techniques applied by Kasemann to determine the variations in seawater acidity and explain why rocks in the Sete Lagoas Formation – located in Brazil between the states of Minas Gerais and Bahia and formed at the bottom of a sea about 550 million years ago – are so different from marine rocks from the same period found in other parts of the world. “These rocks do not show evidence of the explosion of species diversity observed in other seas that existed on the planet at that time,” explains Paula-Santos. “We want to find out to what extent this sea, located in the interior of the continent of Gondwana, was isolated from the others.”
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