Fossils and Relative Dating

Fossils and Relative Dating

Background Information

A fossil is the remains or evidence of an organism. Paleontologists are scientists who learn a lot by studying fossils. They learn (1) how life has changed over time, (2) how Earth’s surface has changed, and (3) what past environments were like. There are 4 types of fossils: petrified, molds and casts, carbon films, and trace fossils. Petrified fossils are fossils in which minerals replace all or part of an organism. Carbon film is an extremely thin coating of carbon on rock. Trace fossils preserve the shapes of part of plants and animals, like leaves or footprints. If the soft parts of the organism decay and the hard parts are dissolved by chemicals, an empty space, called a mold, has the same shape as the organism. Sometimes the mold is filled in by minerals in the sediment. The minerals harden to form a cast, or filled-in mold. The cast is in the same shape as the original organism

Procedure: Making a fossil

1. Each group needs to get a Petri dish. Label the dish with your group number at the side.

2. Grease the inside of the Petri dish with petroleum jelly.

3. Rub a coat of petroleum jelly over the object you are going to use.

4. When your group is ready have Mr. Fix pour plaster of paris to fill the Petri dish. This is simulating sediments burying the organism.

5. When the plaster of paris begins to harden, gently remove the object. You should be able to see the imprint of your object. Set your dish into the cupboard so that it can harden

Analysis/Conclusion Questions

1. What kind of fossil did you make? Explain how you know.

2. In real life, why was there only an imprint left? Explain.

Procedure: Determining the relative age of the fossils

1. According to your dish number, arrange all of the class’s dishes according to which sedimentary layers were deposited in what order. (Teacher will help out).

2. Make a detailed diagram of the layers and label each layer and what fossil organism was in each.

Analysis/Conclusion

1. Explain what the law of superposition is.

2. Based on the above concept, identify which dish represents the oldest strata and which layer the youngest strata. Explain your answers.

3. Identify which fossil was the oldest and which was the youngest. Explain your answers.

4. Explain how sedimentary rock forms. (page 162).

5. The law of superposition determines the relative age of rock layers and the fossils that are in them. Explain what relative age is and how it is different from absolute age. (page 169)

6. Look at figure 15 in your textbook. Explain what an index fossil is (pg 172). Draw the 2 index fossils that are found in only one rock layer each.