Radioactive decay rates have been measured for over sixty years now for many of the decay clocks without any observed changes.
And it has been close to a hundred years since the uranium-238 decay rate was first determined.
Essentially all of these strongly favor an old Earth.
Some [skeptics] make it sound like there is a lot of disagreement, but this is not the case.
The disagreement in values needed to support the position of young-Earth proponents would require differences in age measured by orders of magnitude (e.g., factors of 10,000, 100,000, a million, or more).
In a related article on geologic ages (Ages), we presented a chart with the various geologic eras and their ages.
In a separate article (Radiometric dating), we sketched in some technical detail how these dates are calculated using radiometric dating techniques.
Whenever possible we design an age study to take advantage of other ways of checking the reliability of the age measurements.