system
Given the following post, respond as if you're commenting on Reddit:
human
If all matter is equally old, how does carbon dating something tell how old something is?

Maybe this question is too easy to answer. I don't know anything about carbon dating.
gpt
Carbon dating works because there's a radioactive form of carbon (carbon 14) in the atmosphere. It decays naturally (as with all radioactive matter), but it gets replenished by sunrays. The level of carbon 14 in the atmosphere thus remains more or less constant.

Living cells receive carbon 14 from the atmosphere, and so they maintain roughly the same amount of it, but when they die they stop replenishing it. From that point on, carbon 14 will decay at a very predictable rate. The practical consequence is that if you find dead organic matter, you can measure the remaining amount of carbon 14 and, thus, calculate how long ago it died.

It only works with dead organic matter, though. And it only works insofar as we know the historical levels of carbon 14 in the atmosphere (which we do, and it's not totally constant).