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Have you ever wondered why fossils that are found in recently deposited rock layers more closely resemble existing species than fossils in older layers? Read on and see if you can discover the answer to this question.

The process of fossil formation begins as living things die and are covered with sediment. With time, nature will eventually replace the bones or other hard parts of the critter’s body with minerals. This process preserves a trace of the organism in the rock. More recent fossil remains can be found closer to the surface, while older fossils from animals that died long ago would be found deeper in the earth. For example, more recently evolved animals, like birds, mammals, and modern day lizards, are likely to be closer to the earth's surface than dinosaurs or trilobite fossils. Therefore, scientists may get a general idea as to the age of a fossil by the relative age of the rock layer in which it is found. Also, they can tell the age of the rock by the fossil they find within that rock layer. Because Earth's species have been constantly changing, more recently deposited rock layers would contain fossils resembling the species of today, whereas deeper down, we find fossils of organisms that used to roam the land, but are now extinct.

The following pictures represent an example of this concept:.

This picture represents the surface of the earth now. The lizard is an example of a living organism that lives on the surface and may become fossilized in time.

This picture represents the rock layer where many ancient fossils have been found which date to 400 million years ago. This layer used to be the surface layer and the fossil found here used to live on the surface of the land, just like the lizard. 
This is a picture of a trilobite.  These organisms lived 400 million years ago in a very shallow sea. Scientists are able to determine the age of layers of rocks, plus the environment in which they lived, by studying fossils and rock layers.  Because trilobites lived so long ago, they are often found in layers of rocks that are very old!
The Geologic Column


  • Several sheets of different colored construction paper cut into 4” strips.
  • Scissors
  • Glue stick
  • Tape
  • Three copies of 8 pictures of fossils
Safety concerns: Be sure to keep all sharp safety rules. As with all science lab activities, the most important safety rule is to follow all teacher directions. In this experiment, be especially careful that water does not get onto the floor where you might slip and fall.


  1. Take the pictures of the four oldest fossils.
  2. Cut the strips of colored paper into three roughly equal lengths.
  3. Paste one picture of a fossil onto each of these strips being sure to keep all three pictures of a fossil on the same color paper.
  4. Make one column by taping one of each of these pieces together.
  5. Follow steps 1- 4 using the four younger fossils and different colored strips of paper.
  6. Construct a third column by taping the top picture of the older column below the bottom picture of the younger column. Add another picture from the older column to the bottom and another picture from the younger column to the top. You should now have three partial columns that look like those in the picture below.

  7. Prepare a complete geologic column by taping all eight pictures in order according to the partial columns you have made. You should now have a column that looks like the picture at right.
  1. What do the different colors of paper represent?
  2. Why did you put the younger fossils in the top layers?
  3. What do the partial columns represent?
  4. In which layer would you expect to find a fossil that is very similar to a living species? Why?

Review Science safetey rules here.

Get the plug-ins: Get Adobe Acrobat Reader , and Get Quicktime Player. (The QuickTime plug-in is needed to play sounds and movies correctly.)

Want to share photos of you or your friends doing this activity? Send it in an e-mail with the following information:

  1. The title of the activity
  2. The URL (Internet address)
  3. Your name.

Remember that no pictures can be used that show student faces or student names on it. 

Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 8th grade science core.

Updated October 24, 2008 by: Glen Westbroek

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