system
Given the following post, respond as if you're commenting on Reddit:
human
How is the original amount of C14 in a fossil determined?

When it comes to carbon dating, I understand how the age of a fossil can be determined with the necessary information, being how much C14 is in the current fossil, how fast that C14 deteriorates, and the original amount of C14 in the animal. My question is how the original amount of C14 is determined? Looked everywhere I could and couldn't find an answer, so thank you for any replies.
gpt
It's not the absolute amount of C^14 that matters, but the ratio of C^14 to C^12 in the sample. The atmospheric ratio is held more or less constant by the creation of C^14 from Nitrogen, but once stored inside a body, it will decay to ~~C^(12)~~ N^(14). The longer it has been since the body breathed or ingested, the more C^14 will have turned into ~~C^(12)~~ N^(14).