Left for dead, geologically speaking, the moon is now showing signs of more recent life.
Ever since getting whacked by asteroids and cooked by heat radiating from unstable elements during its violent formation, the moon has cooled. Many things shrink as they cool and the moon is no exception. But tiny valleys discovered in new images from NASA's Lunar Reconnaissance Orbiter (LRO) indicate that the forces causing the moon to shrink were accompanied in some places by other forces acting to pull it apart. This tectonic tug-of-war taking place on the supposedly inert lunar surface surprised scientists. Not only that, it suggests the moon never completely melted in its early stages of evolution—unlike Earth and the other rocky planets—and instead was covered by an expansive ocean of molten rock. Watch the videos below to see evidence of these lunar valleys, called graben, and to learn more about the moon's fascinating geologic past.