"NASA's newest Mars rover has found evidence that a stream once ran vigorously across the area on the Red Planet where the rover is now driving. The finding is a different type of evidence for water on Mars than ever found before. Scientists are studying Curiosity's images of rocks containing ancient streambed gravels. The sizes and shapes of stones cemented into a layer of conglomerate rock are clues to the speed and distance of a long-ago stream's flow."
This video is 51 minutes long so pop some popcorn before you start watching: