In the late Neoproterozoic – an era that lasted from 850 million to 541 million years ago – the concentration of oxygen in the Earth’s oceans and atmosphere rose sharply and for the first time approached today’s level. Geologists have linked this surge to the activity of microorganisms that are capable of performing photosynthesis, like some bacteria, and to the rapid burial of organic matter. A French-Brazilian team now suggests that the mineral pyrite, formed of iron and sulfur, may also have contributed to greater oxygenation of the oceans and atmosphere, which was vital to the appearance of multicellular organisms (Nature Communications, July 22, 2016). The researchers reached this conclusion after examining the proportion of sulfate isotopes in samples of 635 million-year-old glacial mineral deposits in central Brazil and the rate at which bacteria decompose these to form oxygen. “Mineral decomposition occurred rapidly and depleted nearly 60% of the sulfate then available in the oceans, something unprecedented in the history of the planet,” says geologist Ricardo Trindade, professor at the University of São Paulo (USP) and one of the authors of the paper.
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