Thanks for the reply, Studiot. I had an understanding of where the heavier elements originate in photo-planet formation I just didn't know why you'd assume that there would be zero Lead isotopes homogenized within cooled zircon. If there were lead isotopes present among Uranium isotopes at the time of cooling, wouldn't it give the impression that radio-dated samples are older than they actually are? Thank you for the information regardless! I'll take a look at that article here in a bit! Maybe the link will delve into this.
Awesome! Thank you, John. This is what I was looking for. I'll go through this wikipedia article.