This assumption is backed by numerous scientific studies and is relatively sound.
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.
Elements can be transported into a sample or leach out of a sample.
Scientists will reject theories about the age of the earth that do not conform to the norm.
A further example from a lava flow off the coast of Hawaii shows similar discrepancies.