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.

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.

Also, as the authors of the 1968 article were careful to explain, xenoliths cannot be dated by the K-Ar method because of excess argon in bubbles trapped inside [Dalrymple2006].

Thus in this case, as in many others that have been raised by skeptics of old-earth geology, the "anomaly" is more imaginary than real.

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.

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.

Other objections raised by creationists are addressed in [Dalrymple2006a].