A QUIET WORLD
Millions of years passed. The lunar crust cooled, thickened, and stiffened. Collisions continued at a great rate, but because the crust was tougher, impacts began to excavate basins and craters, and to pile up debris around them.
About a billion years after the Moon coalesced, the last few large impacts blasted a handful of basins on the
Moon's Earth-facing side. Pools of dark lava floodet the basins, filling them and spilling over to make the face of the Man in the Moon. Although impacts continued to occur, the rate dropped off dramatically.
Finally, the bombardment all but ceased. For the last j three billion years, the Moon has been a fairly quiet place. At present, it is struck only rarely. The crater Copernicus is 800 million years old, and the most recent major impact formed the crater Tycho about 109 million years ago. Compared to Earth, with its constant erosion, mountain building, and volcanic activity, the Moon is a dead world indeed, although unusual events are sometimes reported by skywatchers).