Why is there a moon?

It's just a piece of rock/star that got caught in earth's orbit a long time ago.

Some theorize that a large object smashed into the Earth and that the moon is actually Earth material that "fell away" from it. With all our tests on the moon and multiple visits there i'm surprised there isn't a more conclusive answer to your question.

	Vector -  1145 pts -  (3 years ago)
	Aye. That large object was Thea. Earth's theorized twin planet that crashed into it and made it roughly it's present size. The debris formed I think was what created the moon.

To control the tides from what I've heard. If it wasn't there, you'd probably be underwater by now. :( So it only makes since that it is there. Other, water-less planets just have a moon to copy us. ;(

Nah...we are just less egotistical and thus have only 1 instead of 20 moons.

It was most likely caused by a crash (as Vector pointed out) and what Chad said is what it does but not what it was meant for :P

The gravitational force from the moon counterbalances that of the Earth which is why it exerts certain push/pull on the waves.

Well, I am not one to believe in purpose, so I will have to say it exists purely through coincidence. It is nice to have as it does some good things for our lowly blue marble planet.