Robert patterson dating
A plot is constructed of Pb-206/Pb-204 versus Pb-207/Pb-204.
However, the test for these assumptions is the plot of the data itself.
While these values do not compute an age for the Earth, they do establish a lower limit (the Earth must be at least as old as any formation on it).
This lower limit is at least concordant with the independently derived figure of 4.55 billion years for the Earth's actual age.
Further, the processes of erosion and crustal recycling have apparently destroyed all of the earliest surface.
The oldest rocks which have been found so far (on the Earth) date to about 3.8 to 3.9 billion years ago (by several radiometric dating methods).