We can assume that the Precambrian rocks already existed when life began, and so the ages of the Precambrian rocks are not necessarily related to the question of how long life has existed on earth.The Cambrian period is conventionally assumed to have begun about 550 million years ago.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.
In general, in n half-lives, only 1/(2^n) of the original parent material will be left.Back to top Radioactive elements decay gradually into other elements.The original element is called the parent, and the result of the decay process is called the daughter element.Since Cambrian and later rocks are largely sedimentary and igneous (volcanic) rocks are found in Cambrian and later strata, if these rocks are really 550 million years old, then life must also be at least 550 million years old.Therefore, my main concern is with rocks of the Cambrian periods and later.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.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.Perhaps the earth was made from older pre-existing matter, or perhaps decay rates were briefly faster for some reason. Geologic time is divided up into periods, beginning with the Precambrian, followed by the Cambrian and a number of others, leading up to the present.When one considers the power of God, one sees that any such conclusions are to some extent tentative. Some fossils are found in Precambrian rocks, but most of them are found in Cambrian and later periods.