Carbon dating margin of error
So the dates derived from C14 decay had to be revised.
One reference on radiometric dating lists an entire array of corrective factors for the change in atmospheric C14 over time.
Some isotopes have very long half-lives, measured in billions or even trillions of years.
Others have extremely short half-lives, measured in tenths or hundredths of a second.
Radiometric dating methods are the strongest direct evidence that geologists have for the age of the Earth.
When I first became interested in the creation-evolution debate, in late 1994, I looked around for sources that clearly and simply explained what radiometric dating is and why young-Earth creationists are driven to discredit it.
The new atom doesn't form the same kinds of chemical bonds that the old one did. It may not even be able to hold the parent atom's place in the compound it finds itself in, which results in an immediate breaking of the chemical bonds that hold the atom to the others in the mineral. (The exact details of this are rather complicated, so I won't go into them here.) When the number of electrons change, the shell structure changes too.
All these methods point to Earth being very, very old -- several billions of years old.
Presented with a new method that gave answers different than existing methods, the scientists involved did not simply assume that either the old method or the new one was wrong.
They viewed the problem as a challenge, dug into it with all their energy, and didn't stop until they understood exactly why their C14 dates disagreed with traditional dates, what was wrong with their C14 procedures, and how to compensate for the problems in the future. When Professor William Libby developed the C14 dating system in 1949, he assumed that the amount of C14 in the atmosphere was a constant.
However, after a few years a number of scientists got suspicious of this assumption, because dates obtained by the C14 method weren't tallying with dates obtained by other means.
A long series of studies of C14 content produced an equally long series of corrective factors that must be taken into account when using C14 dating.