Ocean changes almost starved life of oxygen

Chemical changes in the oceans more than 800 million years ago almost destroyed the oxygen-rich atmosphere that paved the way for complex life on Earth, finds new research involving UCL scientists. Then, as now, the planet had an oxidising atmosphere driven by phytoplankton, which release oxygen during photosynthesis. However, new research published in Nature Geoscience, suggests ocean changes in the early Neoproterozoic era (from one billion to 800 million years ago) may have locked away phosphorus - a vital nutrient for life - limiting phytoplankton growth and oxygen release. Study co-author, Professor Graham Shields (UCL Earth Sciences), said: "The availability of nutrients exerts a major influence on atmospheric oxygen, which in turn sustains complex life. It seems that animals could only gain dominance once the key nutrient phosphate became more widely available, likely through a combination of greater weathering and recycling." The study by researchers at UCL, Lancaster University, University of Exeter and the Chinese Academy of Sciences, suggests the amount of phosphorus available remained just sufficient to support the oxidising atmosphere - preventing a return to the oxygen-poor atmosphere that existed over a billion years earlier. "Ocean chemistry in this period changed to become rich in iron," said first author Dr Romain Guilbaud, of CNRS (Toulouse), previously at Lancaster University. "We know ocean chemistry affects the cycle of phosphorus, but the impact on phosphorus availability at this time hadn't been investigated until now.