Shells on the Mountain Top?

Studying Fossils

Shells on the Mountain Top?

Author: Susan S. Plati
Woodrow Wilson Biology Institute

Target age or
ability group:
Middle and high school.
Class time
One or two 50-minute class periods.
Materials and equipment:
  • fossil containing sediments from two different rock formations
  • pictures or diagrams of some of the fossils that your students may find within the sediments
  • hand lenses or dissecting microscopes
  • blunt probes
  • forceps
  • small hammers
Summary of activity:
In this laboratory activity each group of four students will be given fossil material from a particular formation. Students will work in groups to remove fossils from the sediments, classifying as many organisms and parts of organisms as possible into major groups-mollusks, crustaceans, mammals, fish, etc. Students will then study the data from each formation and make conclusions about the types of organisms and relative age of the organisms in each formation.
Prior knowledge, concepts or vocabulary necessary to complete activity: Students should be familiar with the way in which sedimentary rocks are formed and the knowledge that the oldest rocks are at the bottom of a column of rock. It would be helpful for students to have some understanding of how fossils are formed.

Teacher Instructions

For schools located in areas in which fossil-containing sedimentary rock is available, the teacher can collect samples. Collect enough so that each lab group can have a sample. Where possible, collect samples from two or more strata so that students can compare their group's results with other groups in the class. If you have information about the geological history of the area from which the samples were taken, you may wish to make that available to the class. Another possibility to consider is taking the class on a fossil-collecting field trip to obtain the samples for this activity.

If you do not live in an area that has readily available fossil containing sediments, you can make "fossil sediments" by mixing a variety of shells, bones, and plant parts in sand. Use two different types of sand and vary the organisms found in each "sedimentary formation." Label the two different "formations" on a diagram that shows the strata.

Shells on the Mountain Top?


Charles Darwin was fascinated by some of the shells that he found on the tops of the mountains of South America during his trip aboard the H.M.S. Beagle. He wondered how they ended up so far away from the ocean in which they normally would be found. Ultimately the presence of these fossilized organisms provided Darwin with some of the evidence that helped him to formulate his theory of evolution by natural selection. In this activity, you will have an opportunity to ponder some fossilized organisms in much the same way that Darwin did. You will work in groups to examine some samples of sedimentary rock that contain fossils. You will attempt to separate some of these fossils from the rock in which they are contained by using some tools similar to those that paleontologists use. Finally, you will compare your data to that of other groups and try to reconstruct the environment in which these fossils were formed.

Procedure:(Working in groups of 4:)

1. Obtain a sample of sedimentary rock. Make note of the stratum from which it came. Describe the color, particle size, and any other characteristic features of the sediments that compose the rock sample. Record these data in your lab notebook.

2. Carefully work with the members of your lab group to remove the fossils from the sediments. Use the charts, diagrams, and books provided in an attempt to determine what kinds of organisms are represented by these fossils. Make sketches of the fossils that you find. Record this information in your lab book along with a written description of the fossils and any hypotheses that you may have about the particular identification of the fossil organisms.

3. Compare your data to that of other groups that are examining fossils from the same formation. Enter all these data in the appropriate space of a two column table on the blackboard similar to the one shown on the next page.


Rock Stratum

Description of Sediments
Fossils Observed

(sketches and/or descriptions)
Stratum # 1  
Stratum # 2  

Analysis and Conclusion

Write one or two paragraphs to answer the following questions:

A. What organisms exist in both strata? What is the significance of finding the same organism in both strata?

B. What must the area have been like at the time the various strata were laid down? What hypothetical food chain can you make for each of these times?

C. Which of the sediments is the oldest? Explain the basis for this answer.

D. How would these ancient environments have compared to the environment that exists at similar longitude and latitude today?

On to Studying Living Organisms/Introduction
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