It controls our oceans. It lights the night sky. Wolves howl at it. Ozzy Osbourne barks at it. And man is amazed by it. What is this I speak of? The moon if course! But where did it come from? There are a few different theories behind the origin of our closest celestial body.
The Fission Theory:
This theory states that the moon was originally a part of the Earth. Early in the Earth's formation a rapid spin cast of parts of the crust and mantle into space eventually forming into the moon we know now. The only problem with this theory is that there is no fossil evidence to support the fact that Earth ever had a rapid spin such as this.
This theory states that the moon was formed somewhere else in the solar system. The moon travelled too close to the Earth and got caught in it's gravitational pull. Unfortunately, to get into the present day orbit it would have to have been slowed down just the right amount at just the right time which scientist agree would have been too improbable.
This is one of the simplest theories which states that the Earth and the moon formed at the same time and entered into the orbit of today. If they had however, the moon would have an iron core like the Earth's, but it doesn't.
Giant Impactor Theory:
The most widely accepted theory, this one states that early in Earth's history, an object about the size of Mars struck the planet with the power of one hundred million times that of the comet that killed the dinosaurs. This launched superheated materials into orbit which coalesced into the moon of today. This is so well believed because there is more supporting evidence for this theory than the others.
However, it wasn't always this way. In the 1970's scientists proposed this theory saying that the impact of such a large body would give Earth a rapid initial spin that would have ejected enough material into space to create the moon. For almost ten years, most scientists didn't believe this theory. In 1984, a conference was held comparing the feasibility of the moon creation theories that existed with the Giant Impactor Theory rising as the dominant theory. Models were used to show early planet formation and proved that planetesimal collisions were actually very common in the early stages of the universe.
Unfortunately, these theories are far from fact and it is unknown if we will ever find out how the moon was created. We speculate, and so far the Giant Impactor Theory makes the most sense. Maybe one day...