This video was produced by NASA in honor of 1,000 days in orbit by the Lunar Reconnaissance Orbiter (LRO). It takes viewers through the moon's evolutionary history, and reveals how it came to appear the way it does today. The moon did not always look this way. It likely started as a giant ball of magma formed from the remains of a collision by a Mars-sized object with the Earth about four and a half billion years ago.
After the magma cooled, the moon's crust formed. Then between 4.5 and 4.3 billion years ago, a giant object hit near the moon's South Pole, forming the South Pole-Aitken Basin, one of the two largest proven impact basins in the solar system. This marked the beginning of an era of collisions that would cause large-scale changes to the moon's surface, such as the formation of large basins.
Because the moon had not entirely cooled on the inside, magma began to seep through cracks caused by impacts. Around one billion years ago, it's thought that volcanic activity ended on the near side of the moon as the last of the large impacts made their mark on the surface. Smaller objects continued to batter the moon. Some of the best-known impacts from this period include the Tycho, Copernicus, and Aristarchus craters.