Age/Grade Appropriate

Grades 3 through 4

Observation

Time

Group cooperation if done in small groups

Fossils are frequently found by people other than paleontologists.   Rock collectors, miners, and construction workers may uncover them while working.   Ranchers and hikers may find them exposed in stream beds or on the edges of sod tables.  

Before the nineteenth century, little attention was given to fossils.   Around 1815, an English engineer realized that certain types of fossils were found on only in certain layers of rock.   He also observed that if a layer of rock containing one type of fossil occurred on top of a layer containing a different type of fossil in the same location, then the fossil layers occurred in the same order wherever they were found together.   This observation and the understanding that the bottom layers were formed first gave scientists a means of constructing a geologic history of the earth in which events can be placed in proper order of age.

The relative age of an object or event is its age as compared with that of another object or event.   Finding the relative age simply places things in order of occurrence.   In a group of rock layers, the bottom layer is usually the oldest and the top layer the youngest.   Generally, each layer is younger than the one beneath it and older than the one above it, except when the earth has been moved through natural or human caused events.   This principle is called superimposition because the younger layers are superimposed on the older layers.

Purpose:

To simulate how deposited sediments form layers in the bottom of a sea such as the Inland Pierre Seaway that once covered the Badlands.

Materials:

½ cup each of 3 different colors aquarium gravel
3 small bowls
1 ½ cups soil or sand
Spoon
2 quart rectangular glass baking dish
Tap water
Timer

Procedure

1. Pour one color of gravel into each of the three bowls
2. Add ½ cup soil or sand to each bowl of gravel
3. Use the spoon to mix the gravel and soil thoroughly
4. Fill the baking dish halfway with water.
5. Use your hand to slowly sprinkle the gravel-soil mixture from one of the bowls into the water
6. Wait 10 minutes and observe the appearance of the layer formed by the mixture
7. Sprinkle the gravel-soil mixture from one of the remaining bowls into the water
8. Again wait 10 minutes and observe the appearance of the materials into the dish
9. Add the last gravel soil mixture
10. After 10 minutes observe the contents of the dish