Since there doesn't seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate.However, this causes a problem for those who believe based on the Bible that life has only existed on the earth for a few thousand years, since fossils are found in rocks that are dated to be over 500 million years old by radiometric methods, and some fossils are found in rocks that are dated to be billions of years old.Potassium 40 (K40) decays to argon 40, which is an inert gas, and to calcium.Potassium is present in most geological materials, making potassium-argon dating highly useful if it really works.Thus radiometric dating methods appear to give evidence that the earth and meteorites are old, if one accepts the fact that decay rates have been constant.However, there may be other explanations for this apparent age. I also believe that the evidence indicates that the earth has recently undergone a violent catastrophe.
This gives us the impression that all but a small percentage of the dates computed by radiometric methods agree with the assumed ages of the rocks in which they are found, and that all of these various methods almost always give ages that agree with each other to within a few percentage points.In order to use these methods, we have to start out with a system in which no daughter element is present, or else know how much daugher element was present initially so that it can be subtracted out.We also need to know that no parent or daughter has entered or left the system in the meantime.Assuming we start out with pure parent, as time passes, more and more daughter will be produced. A ratio of infinity (that is, all daughter and no parent) means an age of essentially infinity.By measuring the ratio of daughter to parent, we can measure how old the sample is. Each radioactive element has a half-life, which tells how long it takes for half of the element to decay.