Dating schemes based on rates of radioactivity have been refined and scrutinized for several decades.
Technical details on how these dates are calculated are given in Radiometric dating. As with any experimental procedure in any field of science, these measurements are subject to certain "glitches" and "anomalies," as noted in the literature.
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 use of different dating methods on the same rock is an excellent way to check the accuracy of age results.
If two or more radiometric clocks based on different elements and running at different rates give the same age, that's powerful evidence that the ages are probably correct.
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.The simplest means is to repeat the analytical measurements in order to check for laboratory errors.Another method is to make age measurements on several samples from the same rock unit.Along this line, Roger Wiens, a scientist at the Los Alamos National Laboratory, asks those who are skeptical of radiometric dating to consider the following (quoted in several cases from [Wiens2002]): All of the different dating methods agree--they agree a great majority of the time over millions of years of time.Some [skeptics] make it sound like there is a lot of disagreement, but this is not the case.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.