All forms of isochron dating assume that the source of the rock or rocks contained unknown amounts of both radiogenic and non-radiogenic isotopes of the daughter element, along with some amount of the parent nuclide. Young-Earthers necessarily insist that all ancient isochron ages are really much too old. Such tracers can be used to determine the origin of magmas and the chemical evolution of the Earth. Isochron methods are first introduced in Chapter 6 specifically pp. That is the linchpin of Gill's argument.
Even though you say that they were produced in days or hours, have you not considered where this stratified rock is from?
Historical Geology/Other isochron methods
As the rock cools, minerals form. For example the amount of Rb in mantle rocks is generally low, i. In addition, there is a relatively simple test which can detect mixing in most cases. Any sample taken from the rock has the same amount of P and D. For this purpose, isochron dating was developed, a process "that solves both of these problems accurate date, assumptions at once" Stasson Modern Oceanic Pb - i. As more time passes and a significant amount of radioactive decay occurs, the quantity of P decreases by a noticeable amount in each sample, while the quantity of D increases by the same amount.