In 1896, a French physicist named Henri Becquerel discovered radioactivity in an element called uranium.
He saw that it underwent radioactive decay, or emission of energetic particles to produce new elements.
In fact, Paul already knows that coelophysis lived around 200 million years ago, while iguanodon lived around 150 million years ago.
So, what if Paul found that superus awesomus dinosaur fossil in this middle layer?
In 1905, Ernest Rutherford figured out that we could use radiation to establish the ages of rocks.
By studying how the mass of uranium changed with radioactive decay, Rutherford was able to determine the age of a rock containing a uranium mineral. It meant that scientists could suddenly establish the actual ages of all their rocks and fossils!
And, he also found a coelophysis fossil in the yellow layer. Of course, the coelophysis, which means that coelophysis came before iguanodon.
Again, this doesn't tell them exactly how old the layers are, but it does give them an idea of the ordered sequence of events that occurred over the history of that geologic formation.
Sort of an offshoot of stratigraphic succession is fossil succession, or a method in which scientists compare fossils in different rock strata to determine the relative ages of each.
Along the way, we'll learn how stratigraphic succession and radioactive decay contribute to the work of paleontologists.
Consider the following scenario: Paul the Paleontologist is a very famous scientist who has studied dinosaur bones all over the world.