Other objections raised by creationists are addressed in [Dalrymple2006a].
The overall reliability of radiometric dating was addressed in some detail in a recent book by Brent Dalrymple, a premier expert in the field. 80-81]: These methods provide valid age data in most instances, although there is a small percentage of instances in which even these generally reliable methods yield incorrect results.
Creationist Henry Morris, for example, criticizes this type of "uniformitarian" assumption [Morris2000, pg. But numerous experiments have been conducted to detect any change in radioactivity as a result of chemical activity, exceedingly high heat, pressure, or magnetic field. Scientists have also performed very exacting experiments to detect any change in the constants or laws of physics over time, but various lines of evidence indicate that these laws have been in force, essentially the same as we observe them today, over the multi-billion-year age of the universe.
None of these experiments has detected any significant deviation for any isotope used in geologic dating [Dalrymple1991, pg. Note, for instance, that light coming to earth from distant stars (which in some cases emanated billions of years ago) reflects the same patterns of atomic spectra, based in the laws of quantum mechanics, that we see today.
Here is one example of an isochron, based on measurements of basaltic meteorites (in this case the resulting date is 4.4 billion years) [Basaltic1981, pg. Skeptics of old-earth geology make great hay of these examples.
The simplest means is to repeat the analytical measurements in order to check for laboratory errors.As we pointed out in these two articles, radiometric dates are based on known rates of radioactivity, a phenomenon that is rooted in fundamental laws of physics and follows simple mathematical formulas.Dating schemes based on rates of radioactivity have been refined and scrutinized for several decades.Another method is to make age measurements on several samples from the same rock unit.This technique helps identify post-formation geologic disturbances because different minerals respond differently to heating and chemical changes.The isochron techniques are partly based on this principle.