fighting the good fight on the age of the earth
This is my first post here at RRS. In another forum, I'm involved in a discussion with a young-earth creationist who makes her case primarily (big surprise coming...) by discounting radiometric dating methods, the reality of the geologic column, etc. When I first became involved in the discussion, I was virtually ignorant about the subject, but I have learned (by LOTS of reading) enough to hold my own in the debate, at least with this particular YECer. However, there is one question she has asked for which I'm having difficulty framing an answer.
My understanding is that different types of rocks require different dating techniques. The uranium-lead method, for example, might be appropriate for one type of rock, while a different method, say the Potassium-Argon method, might yield an inaccurate age for that rock. The Potassium-Argon method in particular, according to what I've read, is not suitable for dating younger rocks. Hence, my YECers question: "Some people say that you can't test a rock that is too young. Well, how do you tell if a rock is too young to be tested?"
Seem a fair question--if you don't already know the age of the rock, how do you know if its too young for some particular method to give a reliable date?
I suppose I could point out that the stratigraphic layer in which the rock is found gives a clue to its probable age range, and points toward the technique most likely to yield a reliable date. I doubt she'd be satisfied with this answer or any I'd give...She's likely to argue that its only the assumption of an old earth in the first place on which probable age ranges of stratigraphic layers are based. Can anyone help me understand this better myself, or suggest a way I might head off her likely retort?
Thanks in advance,