how long has the earth existed
Report Abuse. I would think that the moon is about as old as the earth, and would guess that to be about 4.5 billion years. However it is really difficult to document, as none of us where on earth at that time. They use carbon dating to document how much carbon is released from a rock after it is formed. So the 4.5 billion year estimate comes with a disclaimer. It might be off by 4.4 billion years younger, or many trillions of years older than we think it is.