Relative ages are assigned to rocks based on the idea that rock layers lower in the strata were deposited before rock layers that are higher.

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However, there are many methods that can be used to determine the age of the earth or other objects.

The textbooks focus on relative dating, based on the layering of the rocks, and radiometric dating.

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.

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.

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 are three main assumptions that must be made to accept radiometric dating methods.

These must be accepted on faith in uniformitarian and naturalistic frameworks.

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.