(Note that this doesn't mean the half-life of an element is a constant.Different isotopes of the same element can have substantially different half-lives.) It's important to understand that the half-life is a purely statistical measurement. A sample of U238 ten thousand years old will have precisely the same half-life as one ten billion years old.When I first got involved in the creationism/evolution controversy, back in early 1995, I looked around for an article or book that explained radiometric dating in a way that nonscientists could understand. Young-Earth creationists -- that is, creationists who believe that Earth is no more than 10,000 years old -- are fond of attacking radiometric dating methods as being full of inaccuracies and riddled with sources of error. All these methods point to Earth being very, very old -- several billions of years old.Some isotopes can break down in more than one way -- in these cases, each different breakdown type has its own half-life.
I found several good sources, but none that seemed both complete enough to stand alone and simple enough for a nongeologist to understand them.
Thus this essay, which is my attempt at producing such a source.