Further, the processes of erosion and crustal recycling have apparently destroyed all of the earliest surface.
Young-Earthers have several methods which they claim to give "upper limits" to the age of the Earth, much lower than the age calculated above (usually in the thousands of years).
Those which appear the most frequently in talk.origins are reproduced below: Note that these aren't necessarily the "best" or most difficult to refute of young-Earth arguments.
However, they are quite popular in modern creation-"science" literature (even though they should not be!
A young-Earther would object to all of the "assumptions" listed above.
However, the test for these assumptions is the plot of the data itself.
The higher the uranium-to-lead ratio of a rock, the more the Pb-206/Pb-204 and Pb-207/Pb-204 values will change with time.