8. Radiometric dating gives absolute dates.

So the law of superposition gives us the relative age of the fossils.

We can tell that the brachiopods are older than ammonites and younger than trilobites, but how can we determine when they actually lived?

Well again, the secret is in the rocks.

This scientist is looking at the chemical composition of the rocks.

Since the chemical composition has changed through time at a certain rate, we can determine how old rocks are by analyzing their chemistry. This process is called radiometric dating.

Using radiometric dating allows us to find accurate ages for particular layers of rocks.

Let's see how this works.