Ancient rocks are stacked like the layers of a cake in this recent image from the Curiosity rover on Mars. Mission scientists say the layers probably formed several billion years ago, at or near the mouth of a river, as the river deposited sediments carried from up stream. The images confirm that Curiosity's surroundings, inside a large crater, were once warm and wet, providing a possible habitat for life. This image, which is in false color, spans about five feet, so each rock layer is no more than an inch or two thick. [NASA/JPL/MSSS]