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.

Some of the common isotope pairs used are K-Ar, Rb-Sr, Pb-Pb, and U-Pb.

Carbon-14 dating is another common technique, but it can only be used on carbon-containing things that were once alive.

There is also a difference in the timescale used to explain the layers.

Determining the relative age of a rock layer is based on the assumption that you know the ages of the rocks surrounding it.

The method of calculating radiometric dates is like using an hourglass.

You can use the hourglass to tell time if you know several things: the amount of sand in the top of the hourglass when it started flowing, the rate that the sand flows through the hole in the middle, and that the quantity of sand in each chamber has not been tampered with.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.There are three main assumptions that must be made to accept radiometric dating methods.These must be accepted on faith in uniformitarian and naturalistic frameworks.Uniformitarian geologists use so-called dating methods to determine the ages of the surrounding rocks.