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.
For isochrons, which we will discuss later, the conditions are different.
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.
I believe that there is a great need for this information to be made known, so I am making this article available in the hopes that it will enlighten others who are considering these questions.
Even the creationist accounts that I have read do not adequately treat these issues.
How radiometric dating works in general Why methods in general are inaccurate Why K-Ar dating is inaccurate The branching ratio problem How Errors Can Account for the Observed Dates Why older dates would be found lower in the geologic column especially for K-Ar dating Do different methods agree with each other on the geologic column?