Whenever possible we design an age study to take advantage of other ways of checking the reliability of the age measurements.The simplest means is to repeat the analytical measurements in order to check for laboratory errors.Radioactive decay rates have been measured for over sixty years now for many of the decay clocks without any observed changes.
A recent survey of the rubidium-strontium method found only about 30 cases, out of tens of thousands of published results, where a date determined using the proper procedures was subsequently found to be in error.
One question that sometimes arises here is how can scientists assume that rates of radioactivity have been constant over the great time spans involved.
147] has highlighted the fact that measurements of specimens from a 1801 lava flow near a volcano in Hualalai, Hawaii gave apparent ages (using the Potassium-Argon method) ranging from 160 million to 2.96 billion years, citing a 1968 study [Funkhouser1968].
In the particular case that Morris highlighted, the lava flow was unusual because it included numerous xenoliths (typically consisting of olivine, an iron-magnesium silicate material) that are foreign to the lava, having been carried from deep within the earth but not completely melted in the lava.
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.
Such failures may be due to laboratory errors (mistakes happen), unrecognized geologic factors (nature sometimes fools us), or misapplication of the techniques (no one is perfect).
We scientists who measure isotope ages do not rely entirely on the error estimates and the self-checking features of age diagnostic diagrams to evaluate the accuracy of radiometric ages.
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.
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.