Application of carbon dating
C-14 is used often in dating artifacts from humans.
For determining age of fossils older than 60,000 years one uses a potassium-argon dating technique.
You probably have seen or read news stories about fascinating ancient artifacts.
At an archaeological dig, a piece of wooden tool is unearthed and the archaeologist finds it to be 5,000 years old.
Potassium dating has a half life of 1.3 billion years, thus allowing the age of rocks several billions years old to be determined.
A more accurate "argon-argon" dating technique (determining the ratio between argon-39 and argon-40) has also been developed.
In other words, the further you go back, the more you have to shrink the radiocarbon dates to make them fit the facts.
It is assumed that the ratio has been constant for a very long time before the industrial revolution. (For on it hangs the whole validity of the system.) Why did W. Libby, the brilliant discoverer of this system, assume this?
Libby knew that C was entering and leaving the atmosphere (and hence the carbon cycle).
The article is in straightforward language and the non-technical reader could profitably work through it.
C, we find that this ratio is the same if we sample a leaf from a tree, or a part of your body.