A Question of Time: Radioactive Dating Methods
Numbers enjoy a special status in our culture. They have an almost magical way of authenticating the statements they embellish. A published report containing figures as well as facts will have better success and command greater respect from its readers than one without figures. The problem is that sometimes people use questionable statistics to bolster their ideas and pass them off as fact to unsuspecting people.
Have you ever read in the paper a headline such as "50-Million-Year-Old Bat Fossil Confirms Theory"? How do researchers arrive at the such a large figure, and how certain are they of its accuracy? If you study the biblical account of Creation, Scripture seems to indicate an earth that is between eight thousand and fifteen thousand years old, which would also imply that living things have been here for the same amount of time. Why such a discrepancy?
Even devoted evolutionists admit that the theory of evolution is doomed if it does not have one very important ally on its side: time. They take the approach that given enough time (roughly 3/5 billion years) anything can happen, including evolution. Evolutionists use dates of billions of years as if they were common knowledge – and anyone who challenges these dates is being "unscientific." So evolutionists have asserted that the earth is billions of years old and have also devised radioactive dating techniques to "prove" the ages of fossils and rocks.
Estimates concerning the ages of rocks and fossils run into the millions and billions of years based on the so-called "long-term" dating methods: uranium-lead, potassium-argon, and rubidium-strontium. In each of these methods, an unstable original material is changing by radioactive decay to a stable end product. Uranium decays to lead in a series of alpha and beta decay reactions. Potassium decays to argon in a single step, and rubidium decays directly to strontium. It takes a certain amount of time for this decay process to occur. When a scientist measures the amount of argon in a rock sample, he can calculate the approximate age of rock assuming that when the rock was "formed." it contained only potassium. That would be similar to measuring the amount of gasoline in the gas tank of a car after a trip and estimating how much time has elapsed since the beginning of the trip.
These "long-term" dating methods are not deceptive in themselves, but the scientist who uses them must make some basic assumptions that he has no way of verifying. For example, the scientist using the potassium-argon dating method has no way of knowing how much argon was originally present in the sample. Assuming there was no argon present when the rock was formed is foolish, since it has been proved that rocks of known age and formation (volcanic rocks) have been found with an abundance of argon [Andrew A. Snelling, "The Cause of Anomalous Potassium-Argon 'Ages' for Recent Andesite Flows at Mt. Ngauruhoe, New Zealand, and the Implications for Potassium-Argon 'Dating'" (paper presented at the Fourth International Conference on Creationism, Pittsburgh, PA, August 1998)]. The problem with these dating methods is that a key ingredient of the scientific method – observation – is missing.
Another assumption is that the radioactive decay rate is constant. Scientists use the principle of half-life to describe how long it takes for an isotope to decay. A 1.0-gram sample of iodine-131 will be present at 0.50 gram after only 8.0 days. So the half-life of iodine-131 is 8 days. Many radioactive isotopes have half-lives that have never been directly observed but rather extrapolated (graphing a projected trend). Uranium-238 is a good example because it is said to have a half-life of 4.51 billion years.
Obviously, scientists had to extrapolate that figure assuming that uranium has decayed at a constant rate since the origin of the universe. But we really do not know whether the rate of isotope decay is constant or not.
As you can see, these dating methods rely on some questionable assumptions. The main problem, however, with these "long-term" dating methods is in the interpretation of the results. Evolutionists say that these dating methods prove that the earth's rock layers are old, and therefore evolution occurred. But all that these methods ever really show is the amount of end product present within a rock, and that result can be interpreted many different ways. In fact, there are many Creationists who say some dating methods are accurate, and they have various theories to reconcile old-earth estimates and the Creation week described in Genesis 1. But on the whole, Christians who believe in a literal six-day Creation are skeptical of old-earth estimates. The general mistrust that believers have for dating methods to understandable, considering that evolutionary theory was considered "scientific fact" long before radioactive dating techniques were developed.
Carbon-14 dating is a short-term dating method that is often used to determine the ages of fossils and manuscripts. Cosmic rays from the sun produce a heavy isotope of carbon with two extra neutrons – carbon-14. It decays at a constant rate and has a half-life of 5730 years. Carbon-14 properties are identical to those of carbon-12; and all living things, plants or animals, always contain a certain amount of carbon-14. When an organism dies, no more carbon-14 is taken in by the dead organism, and the isotope gradually decays to nitrogen. By measuring the amount of carbon-14 left, scientists can determine the approximate time of the organism's death. Most scientists would agree that carbon-14 dating gives accurate calculations for living things since they have an abundance of carbon molecules. The carbon-14 method starts to lose accuracy for organisms over 3000 years old, partially because scientists have determined (using tree rings) that C-14 levels in the atmosphere fluctuated significantly prior to 1000 B.C. As with the other dating methods, C-14 data is useful only if the limitations are recognized.
Taken from The Physical World: An Introduction to Physical Science for Christian Schools, by Terry Egolf and Donovan Hadaway, Greenville, SC: Bob Jones University Press, 2000; pages 124-125.