Mars pebbles prove that rivers altered the planet's surface

Scientists already had an inkling that water helped form the landscape on Mars, but they're now ready to confirm that claim. In a report written for Science, researchers state that the smooth, rounded shape of the Red Planet's pebbles and the way they overlap is identical to the gravel formation found in Earth's rivers. They appear to be too large to be blown by wind, and their varied shades indicate they were transported from various locations -- telltale signs of a former stream. "For decades,...