The Language of God: A Scientist Presents Evidence for Belief

by Francis S. Collins

We now know that the universe is approximately 14 billion years old. A century ago, we didn’t even know how long our own planet had been around. But the subsequent discovery of radioactivity and the natural decay of certain chemical isotopes provided an elegant and rather precise means of determining the age of various rocks on Earth. The scientific basis of this method is described in detail in Brent Dalrymple’s book The Age of the Earth, and depends upon the known and very long half-lives by which three radioactive chemical elements steadily decay and transform into different, stable elements: uranium slowly becomes lead, potassium slowly becomes argon, and the more exotic strontium becomes the rare element called rubidium. By measuring the amounts of any of these pairs of elements, we can estimate the age of any particular rock. All of these independent methods give results that are strikingly concordant, pointing to an age of Earth of 4.55 billion years, with an estimated error of only about 1 percent.