Biological soil crusts are found in every desert in the world, including the driest desert on Earth—the Atacama in Chile—where the rainfall can be less than 1 millimeter per year. Although soil crusts are variable in composition, they generally develop when microscopic algae and fungi, lichens, and mosses grow on and in the soil surface, entwining and adhering soil particles to form a matrix that helps to stabilize the soil.

Soil stabilization is especially important in arid areas where there are large expanses lacking plant cover. Dozens of studies have found that soil crusts reduce or completely eliminate erosion of soil by water and wind that would otherwise be widespread in these areas. Biological soil crusts also trap soil moisture, fix nitrogen from the atmosphere, and provide sheltered areas for plants to germinate and grow.