Start Relative age dating superposition

Relative age dating superposition

Fossil succession is based on the observation that certain assemblages, or groups, of animals and plants have lived during certain time periods over geologic history.

The upper layer had scallop fossils, and the lower layer had trilobites.

Smith would have brought these two arrangements together, overlapping the common scallop layer, to produce a larger succession of three rock strata!

We'd want to use a more short-lived fossil, like the dodo bird.

We also want our index fossils to be common, widely-distributed species that are easy for scientists to identify.

They follow an ordered progression that is very clear and predictable.

Therefore, we can use the succession of fossil assemblages to establish the relative ages of rocks.

We talked about relative dating of rocks and how scientists use stratigraphic succession to compare the ages of different rock layers.

You should already understand that the lower rock strata are generally older than the strata found higher up in the rock.

An index fossil is a fossil representing a plant or animal that existed for a relatively short duration of time.

These are the fossils that we want to use for relative dating.

Well, let's go back to our surveyor, William Smith.