Historical artefacts: How old are they?

We've all seen those amazing historical artefacts in museums and read about how old they are, what they were used for, who they were made for and used by. Have you ever wondered how this information is discovered? How could it possibly be known that some seemingly useless tool or weapon is 11000 thousand years old when we weren't there ourselves? Well, it's all about the radioactivity of the carbon in that artefact, and it is the job of archaeologists to examine historical artefacts.