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How to Use Fossils to Correlate Rocks

Geologist use fossils to correlate, or match up, rocks between regions of the world. These fossils are able to provide the relative age of a rock layer. The relative age is not an exact number, but a determination of whether the rock is older or younger than the surrounding rocks. Some fossils, known as index fossils, lived during a short time period and are able to provide relative, as well as approximate, age in years.

Things You'll Need

Rock samples
Hand magnifier
Stratigraphy profile for each area
Large sheet of paper
Colored pencils

Instructions

- 1
  Sketch a stratigraphic profile for each area of your study on either end of a large piece of paper. The profiles should show representations of the soil and rock layers providing information such as thickness, color and classification. Note any unusual characteristics of the soil and rock layers. These unique characteristics are useful in conjunction with the fossil data.
- 2
  Examine the rocks with fossils and determine the type of fossils present. Identify as many fossils as you can in each rock sample. Particularly look for index fossils. Lists of common index fossils are available from the United States Geological Survey if you are unfamiliar with their identification. Add the fossil information to the soil profiles of each area using different color codes for specific fossils or groups of fossils. Record all data such as fossil type, numbers of samples and unusual characteristics on the profile with the corresponding rock layers.
- 3
  View the soil profiles side by side. Look for fossils or fossil groups that are similar in each profile. The color-coded map will help the fossils and fossil groups stand out. Use the similar fossils or groups, especially if they are index fossils, to correlate the rock layers. You can draw lines connecting the rock layers with the similar fossil types.

Rocks & Minerals