Mongol Els Sand Dunes (image) Max Planck Institute for the Science of Human History Share Print E-Mail Caption The sand dunes of Mongol Els jutting out of the steppe in Mongolia. Many of these desert barriers only appeared after the Last Glacial Maximum (~20,000 years ago). Credit Nils Vanwezer Usage Restrictions This image may only be used in the context of reporting on this publication and with appropriate credit information. Share Print E-Mail 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.