When we gaze up at the Moon, we expect a certain degree of consistency. Sure, it moves through its phases, shifting in and out of darkness over the course of the month, but generally speaking, the Moon's surface looks the same to us — night after night, year after year. But the Moon has not always looked the way it does now.
In the last 4.5 billion years, the Moon has transformed from a roiling mass of ejected terrestrial matter, to an unblemished orb, to the heavily cratered, volcanic-crust laden entity we know and love today. We know these things occurred because the Moon's surface features tell a story, and for close to three years now, NASA's Lunar Reconnaissance Orbiter has been getting an up close look at what those features have to say.