By Jane E. Allen Associated Press PASADENA, Calif. _ Mars is looking more Earthlike and less like the moon with Pathfinder scientists' every new observation, including a football-sized martian rock that fits the profile of a kind common on Earth. The first chemical analysis of the martian rock _ nicknamed Barnacle Bill by Pathfinder scientists _ shows that at least one rock on the dusty red planet is rich in silica, the quartz material found in sand. Such a rock _ which could have been brought to the surface by volcanic activity or a meteorite impact _ could only be formed by repeated heating in an active crust, scientists said Tuesday. ``The Earth is a very unusual place, at least we thought that until last night,'' said Hap McSween, a meteorite specialist from the University of Tennessee. ``Now it appears Mars, too, has a crust that ... contains quartz.'' Examination of a second rock was expected to begin today, with its chemical signature taken overnight by the Mars Pathfinder's robot geologist Sojourner. Data from the rover suggest that Barnacle Bill might be a kind of andesite, the second most common type of lava on Earth. It gets its name from the Andes Mountains. The latest evidence hints that water may have existed on Mars more than 4 billion years ago, the same era when life began on Earth. It was too early to tell if Barnacle Bill is andesite. But because some types of andesite only form in the presence of water, the new results eventually may lead to the demonstration that early Mars had water in its interior, said Allan Treiman, a planetary scientist at the Lunar and Planetary Institute in Houston. ``It completely changes most people's views of Mars. Mars becomes a place that had water from the beginning and the water was very active in the planet,'' Treiman said in a telephone interview just as scientists were finishing a news conference at NASA's Jet Propulsion Laboratory. Matthew Golombek, the Pathfinder project scientist at JPL, was far more cautious in his assessment. But he was excited just to see that Mars' crust was a ``much more dynamic'' place than originally perceived, ``more like Earth than the moon,'' with re-melting of rocks that heated away elements like iron and left more silica. ``What we don't know is whether that's an andesite,'' he said, and not some other rock types, like a mix of granite and basalt, the most common type of lava on Earth. On Monday, Pathfinder scientists presented evidence of massive floods 1 billion to 3 billion years ago on Mars' now bone-dry salmon-colored surface. With other rocks named Yogi, Scooby Doo, Casper and Crab due for similar up-close encounters with Sojourner, scientists' conclusions could strengthen with numbers. ``This site really is a rock festival,'' quipped McSween.