In his book, "The Once and Future moon" (1996), Spudis discusses some common theories and how exploration has helped us narrow down the possibilities.
Some thought the moon broke off from the Earth early in its formation and was trapped in orbit. Others said the moon was a galactic wanderer that came close enough to the Earth to be captured by its gravity. Another theory proposed that a huge rock crashed into the Earth knocking a chunk of it loose that formed into the moon. (This is sometimes called the "big whack" theory.)
When the Apollo astronauts went to the moon, we learned a lot more about its composition. The astronauts left seismographs to measure "moonquakes" and laser reflectors that are still in use. They bounce back laser pulses sent from Earth.
The rocks the astronauts brought back helped determine the age of the moon. They also hinted that the moon had an ocean of magma early in its history. These and other discoveries helped point scientists toward the "big whack" model. More research is needed to say for sure. Lunar research has also given us insights into the Earth, the solar system, and the universe.
So when are we going back to the moon to learn more? Will there ever be colonies there? NASA has no specific plans for moon missions, but it is exploring many possibilities. One is a lunar outpost where scientists could study the moon and the universe and possibly mine elements needed on Earth.
How would you design such an outpost? Consider these factors:
Air: The moon has no air. If you want to breathe, you'll have to bring a supply of air or manufacture it from elements on the moon. It's very expensive to fly anything from Earth, so you'll probably want to find a way to make your own air on the moon.
Food: There's no food on the moon either. But there are basic elements that make up food, including nitrogen, carbon, oxygen, and potassium. Could they be used to supply nutrition or breathable air?
Water: The only water on the moon is in the form of ice. Ice has been detected near both lunar poles. Oxygen could be manufactured from water.