That means the intake and output must be equal all the time. To decide that, one must understand where it comes from and where it goes.
C-14 is constantly being created as cosmic rays from outer space smash into atoms in earth’s atmosphere.
For a constant rate of output, a constant rate of organisms (including vegetation) must be assumed.
The atoms in some chemical elements have different forms, called isotopes.
These isotopes break down at a constant rate over time through radioactive decay.
However, to figure this out irrefutably, three things must be known for the equation: the rate of decay (half-life), got it; the amount of C-14 presently in the fossil, got it; and the amount of C-14 in the organism when it died, um, DON’T have it. To determine how much C-14 was present when an organism died, scientists look at how much C-12 the fossil contains. So, if it can be determined what the ratio of C-14 to C-12 was, it can be presumed how much C-14 was in an organism when it died. That this ration has always been constant, however, cannot be proven.
Instead of throwing this equation to the wind, however, scientists make an and call their resulting findings fact. In fact, there’s good evidence the ratio fluctuates, because the amount of C-14 present in the atmosphere fluctuates.