system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When trying to carbon date an ancient man-made object, how do you differentiate between when the object was created and the age of material that was used to create the object?

Example: An ancient sword can be made out of cast iron. When you carbon date it today to find its age, are you finding the age of the iron or are you finding the age of the sword?
gpt
> When you carbon date it today to find its age, are you finding the age of the iron or are you finding the age of the sword?

Carbon dating is only used on biological material in comparison to the levels in the atmosphere at the time. So in your example we would date the leather wrapping on the handle to see when the cow died and assume they didn't use leather from a cow who died hundreds of years prior.

The reason it works is that some carbon is radioactive and when it is tied up in an organism it rotates through them regularly. Once they die it doesn't go anywhere and the radioactive atoms decay at a known rate, so by looking at the different proportion we can know when the organism died.