A rock sample from Nigeria was dated at 95 million years by the potassium-argon method, 750 million years by the uranium-helium method, and less than 30 million years by the fission-track method.
If the clock is not set to zero when a deposit forms, then there can be no starting point from which to calculate the age of a deposit.
Some scientists argue that the magnetic field of the earth has declined over time.
Thus radioactive dating relies purely on assumptions.
For more on this subject, see the video Bones in Stones i. Ogden III, "Annals of the New York Academy of Science," 288 (1977): 167-173.
The Shroud of Turin, a linen cloth that tradition associates with the crucifixion and burial of Jesus, has undergone numerous scientific tests, the most notable of which is radiocarbon dating, in an attempt to determine the relic's authenticity. Shredding the samples would not solve the problem, while making it much more difficult and wasteful to clean the samples properly.
It's assumed that the clock was set to zero when the study material was formed.
This requires that only the parent isotope be initially present or that the amount of daughter isotope present at the beginning is known so that it can be subtracted.
Many examples from literature show that the zero-reset assumption is not always valid.