It is possible to measure the ratio of the different radioactive parent isotopes and their daughter isotopes in a rock, but the ratios are not dates or ages.The dates must be inferred based on assumptions about the ratios.Uniformitarian geologists use so-called dating methods to determine the ages of the surrounding rocks.
Determining the relative age of a rock layer is based on the assumption that you know the ages of the rocks surrounding it.
If any of these three conditions is not accurately known, the hourglass will give an inaccurate measure of time.
Radiometric dating is based on the fact that radioactive isotopes decay to form isotopes of different elements.
The reason this age may not be a true age—even though it is commonly called an absolute age—is that it is based on several crucial assumptions.
Most radiometric dating techniques must make three assumptions: The major problem with the first assumption is that there is no way to prove that the decay rate was not different at some point in the past.