Acid oceans cited in Earth's worst die-off
2015
Hand, Eric
The Permian mass extinction, 250 million years ago, was the worst in Earth's history, killing off some 90% of living species. A team of European geoscientists has found the most direct evidence yet that ocean acidification was a major part of the die-off. Scientists have long suspected that volcanoes dumped trillions of tons of carbon dioxide into the atmosphere and that some of it dissolved in the oceans, leading to an acidity that can weaken sea creatures' ability to make calciferous shells. Now, locked in limestone that was formed in shallow seawater offshore of the supercontinent Pangaea, scientists have found an isotopic signal to support a sharp drop in pH. The catastrophe holds a cautionary lesson: Due to the burning of fossil fuels, today's oceans are acidifying at an even faster rate than they were at the time of the extinctions, although it hasn't yet persisted nearly as long.
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