NASA says its Curiosity rover has found evidence an ancient stream may have flowed vigorously on Mars. While there has been earlier evidence of the presence of water on Mars, images returned by the rover of rocks containing ancient streambed gravels are the first of their kind, NASA\'s Jet Propulsion Laboratory in Pasadena, Calif., reported. The images show stones cemented into a layer of conglomerate rock, and the sizes and shapes of stones offer clues to the speed and distance of the long-ago stream\'s flow, JPL scientists said. \"From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep,\" said Curiosity science co-investigator William Dietrich of the University of California, Berkeley. \"This is the first time we\'re actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it.\" The ancient stream bed lies between the north rim of Gale Crater and the base of Mount Sharp, a mountain inside the crater that is Curiosity\'s main research destination because clay and sulfate minerals detected there from orbit can be good preservers of carbon-based organic chemicals that are potential ingredients for life, JPL said.