While the diversification and evolution of much Precambrian early life may have temporarily halted in the deep oceans, it probably continued in lakes, reports a paper in Nature Communications. Previous work has highlighted a shortfall of molybdenum (a trace metal necessary for eukaryotic and nitrogen-fixing bacterial life) in the Precambrian oceans, which implies that the evolution and diversification of many organisms was delayed.
John Parnell and colleagues now provide new data from the Torridonian sedimentary rocks of northwest Scotland showing that lake sediments from the Precambrian contained a high concentration of molybdenum. These sediments also feature records of annual layering, allowing the average yearly flow of molybdenum into the lake to be measured and showing that levels of molybdenum were 1 to 2 orders of magnitude greater than those present in the marine environment. These consistently high levels and the suggestion that metals such as molybdenum were bioavailable in the Precambrian Scottish lake mean it may have been a suitable environment to allow the expansion of nitrogen-fixing cyanobacteria and the diversification of eukaryotes.