This is to express my appreciation for your well-considered editorial (March 3), "Dogma on the Rocks," in response to the attacks on the overwhelming evidence for the age of the Earth being billions, rather than thousands, of years.
This evidence involves the calculation of the degree of decay of several long-lived radioactive isotopes since the formation of the Earth. Knowing the rates of decay of these isotopes, we can calculate the age of the Earth. While not in exact agreement, a variety of methods agree in estimating a geological age on the order of billions of years.
Bill Hoesch of the Institute for Creation Research and others attack these results on three main grounds: (1) a claimed lack of knowledge of the original abundance of these isotopes; (2) the supposition that rates of decay of these isotopes have varied in unknown ways over geological time; (3) short-lived isotopes may have disappeared by other methods than radioactive decay. Although lack of space prevents me from going into the fallaciousness of these attacks, I can cite very clear evidence that the Earth is much older than 6,000 years.
This argument runs as follows. Of the 32 known isotopes with half-lives between 10,000 and 10 million years, the only three that exist naturally on Earth are those that are continually replenished by the decay of other isotopes. Since 6,000 years would not be nearly enough time to allow for near-total decay of these isotopes, supporters of a young Earth would have to find special reasons for the lack of natural occurrence of 29 different isotopes.