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.
If these conditions are not satisfied, the error can be arbitrarily large.
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.
Potassium is about 1/40 of the earth's crust, and about 1/10,000 of the potassium is potassium 40.
Uranium decays to lead by a complex series of steps. Thus we obtain K-Ar dating, U-Pb dating, and Rb-Sr dating, three of the most common methods.
Back to top Radioactive elements decay gradually into other elements.