Start Fossils dating rock

Fossils dating rock

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

Let's say in the first outcrop, he found an upper rock layer containing ammonite fossils and a lower layer containing scallops.

In the second outcrop, miles and miles away, he also found two layers; but these layers were different.

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.

When a scientist finds a section of rock that has lots of different strata, he assumes that the bottom-most layer is the oldest, and the top-most layer is the youngest.

But sometimes, a scientist finds a couple of rock outcrops that are separated by a wide distance.

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

He was often presented with the problem of finding two different rock outcrops from two different periods.

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.

For example, human beings and modern elephants are part of the same assemblage because we live in the same time period.

Free 5-day trial You may already know how to date a fossil with a rock.