Every year, billions of tons of valuable soil are lost worldwide through erosion, much of it deposited in bodies of water that fill with sand or silt as a result. Soil losses measured in Germany range from 1.4 to 3.2 tons per hectare per year; in extreme weather, the figure can be as high as fifty tons. Geoscientists at the University of Tübingen have now shown how biological soil crusts provide a protective layer against erosion. Natural "carpets" of bacteria, mosses, lichens, fungi and other organisms bind soil particles into coherent layers, or crusts.