What is radiometric dating? Does it fit with the view of a young earth?
Radiometric dating is the way that scientists determine the age of matter. Radiometric dating techniques are applied to inorganic matter (rocks, for example) while radiocarbon dating is the method used for dating organic matter (plant or animal remains). The idea of a young earth, as presented in the Bible, is not compatible with the findings of radiometric dating.
What does this mean for Christians? Are we forced to accept that the Bible is inaccurate or not literal, based on what radiometric dating has found? It's a good question. First, let's look at what radiometric dating is, and how scientists determine the age of matter.
Radiometric dating is based on the rate of decay of certain isotopes, which is defined as: "each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element." The isotope Uranium-238 (U238) is one of these unstable, radioactive isotopes. Over time, U238 decays and goes through many unstable stages, until it finally becomes stable as Lead-206 (Pb206). U238 is the "parent" isotope, and Pb206 is the "daughter" isotope.
Scientists found that by measuring the amounts of both parent and daughter isotopes in matter (seeing how much of the U238 has stabilized into Pb206), they could accurately calculate the age of that matter. For example, it takes 4,460,000,000 years for half a sample of U238 to turn into Pb206. So, if they found a rock that contained an exactly equal amount of these two isotopes, they could date that rock at exactly 4,460,000,000 years old.
There is no question that radiometric dating is accurate—provided that certain assumptions are true. First, we must assume that the rate of decay of U238 into Pb206 has remained constant over time. Second, we have to assume that no other chemical processes have adulterated the rate of decay (no amount of either parent or daughter has been added or taken away from the specimen). Third, we have to assume we know how much of each the parent and the daughter were present at the beginning of the decay process. The rate of isotope decay will always remain the same, but the accuracy of radiometric dating depends on these assumptions being correct for the specimen in question.
Assumptions two and three are not by any means certain, because how can we really know, having not watched the specimen over its entire life, how much of each isotope was present at the beginning, and whether or not anything was added or taken away? We can't know, so scientists are working on reasonable guesswork there. However, the first assumption (that the rate of isotope decay has remained constant over millions of years) has always been pretty much unquestionable—until recently. New research has found evidence to suggest that isotopes decayed at different rates in the unobservable past. This research is based on yet another element, called helium.
Helium is a gas—very light, with very small atoms, and is unreactive. Helium is a byproduct of the decay process of U238 into Pb206. As the uranium isotopes pass through their unstable stages on the way to becoming lead isotopes, they let off helium. Now, scientists found some crystals called zircons within granite specimens, which still contain a good deal of helium. According to radiometric dating, these zircons (and the surrounding granite) should be 1.5 billion years old. But if that were true, the helium, because of its nature, would have escaped from the rock over that much time (its atoms are smaller and lighter than the atoms of the zircons). However, there was still plenty of helium inside the zircons. It should have slowly seeped out, but it didn't. Because of this, scientists can now assume that the zircons, and the surrounding granite (a type of Precambrian granite that is the same across the entire planet) cannot be more than 4,000 to 14,000 years old.
New research has determined that radiometric dating is not an infallible method. This example shows that there is still so much that we do not know. Scientific discovery is important, and should never be discouraged, but when it contradicts the Bible, it is rational for Christians to reserve judgment and wait for further evidence to be revealed.