Two methods used for dating fossils
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.
Let's say that Paul the Paleontologist found an iguanodon fossil in the light green layer shown above.
This is just a fancy term for the way rock layers are built up and changed by geologic processes.
Scientists know that the layers they see in sedimentary rock were built up in a certain order, from bottom to top.
And, he also found a coelophysis fossil in the yellow layer. Of course, the coelophysis, which means that coelophysis came before iguanodon.
In fact, Paul already knows that coelophysis lived around 200 million years ago, while iguanodon lived around 150 million years ago.
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Adrian Grahams began writing professionally in 1989 after training as a newspaper reporter.
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When they find a section of rock that has a lot of different strata, they can assume that the bottom-most layer is the oldest and the top-most layer is the youngest.
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.
Stratigraphic and fossil succession are good tools for studying the relative dates of events in Earth's history, but they do not help with numerical dating.