Radiometric age dating accuracy
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.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.For isochrons, which we will discuss later, the conditions are different.If these conditions are not satisfied, the error can be arbitrarily large.In two half-lives, half of the remainder will decay, meaning 3/4 in all will have decayed.
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.
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.
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.