Biological Soil Crust (image) DOE/Lawrence Berkeley National Laboratory Caption This looks like ordinary dirt but it is a biological soil crust (BSC), a living mantle of soil particles bound together by microbes and their by-products. BSCs are common to the arid and semiarid lands that make up about 40-percent of Earth's total land mass. Credit (Photo from Ferran Garcia-Pichel, Arizona State University) Usage Restrictions with permission of Ferran Garcia-Pichel, Arizona State University Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.