Tony; I did see one other thing about radiometric dating that perhaps you could clarify. - I can't help. I understand how they use ratios, but after that I don't have enough knowledge. I admit I've simply accepted that radiometrics work and the different elements used agree with each other within 10-15%.-This Wiki article is very helpful. Each method has time limits but uranium/lead goes back well over 2 billion years:-http://en.wikipedia.org/wiki/Radiometric_dating