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Lesson 2- What are the different kinds of fossils?

Aims:

1. What is a mold fossil?

2. What is a trace fossil?

3. What is a cast fossil?

4. What is a true form fossil?

Motivation: Ask students if they know what the different types of fossils are. Can they describe different kinds of fossils? Show the following types of fossils, taken from http://enchantedlearning.com/subjects/dinosaurs/dinofossils/Fossiltypes.html and discuss each one. The first picture is a fossil in amber, the second one is a trace fossil, the third is a mold fossil, and the last one is a cast fossil.

Procedure:

1. Students are to go to http://zoomschool.com/subjects/dinosaurs/dinofossils/Fossiltypes.html and http://oum.ox.ac.uk/children/fossils/whatfos2.htm and read about the four types of fossils and fill in the following database. Students are to give a picture example of each as well. Click here for a student database.

Type of Fossil	How the Fossil Was Formed	Picture Example
Mold Fossil	a fossilized impression made in the substrate - a negative image of the organism
Cast Fossil	formed when a mold is filled in
Trace Fossil	fossilized nests, gastroliths, burrows, footprints, etc
True Form Fossil	fossils of the actual animal or animal part

Activities: Children are going to create models of the different types of fossils!

1. To create a mold and cast fossil go to http://zoomschool.com/subjects/dinosaurs/dinofossils/Fossiltypes.html. I have found a very easy way to get both fossils in the same lesson.

Problem: How can we make a mold and cast fossil?

Hypothesis: We think by making an imprint of an object and placing it in clay then we can make a mold fossil. We think if we fill the mold fossil with Plaster of Paris then we can make a cast fossil.

Materials: Different objects to make an imprint with, bowl, water, Plaster of Paris mix (available at all craft or hardware stores), mixing spoon, clay, cooking oil, small paintbrush, and sentence strips (for an oaktag ring).

Procedure:

1. Flatten and smooth the clay to about 1/2 inch thick and slightly larger than the object you wish to imprint.

2. Press the object firmly into the clay, then remove carefully. You have now created a mold fossil.

3. Brush the mold fossil lightly with cooking oil.

4. Using the sentence strip, encircle the imprint and press the strip into the clay. You should now have a ringed "cup" around the imprint.

5. Prepare the Plaster of Paris mix according to the package directions.

6. Pour mix into the "cup" about an inch thick. Shake to settle the mix and get a smooth top.

7. Let dry for about an hour.

8. Remove ring and hardened mix. The Plaster of Paris has now created a cast fossil.

9. Have students compare the two fossils. How are they different? Alike?

2. To create a trace fossil, have students log onto http://museum.vic.gov.au/dinosaurs/activ.html . I have reprinted the activity here:

How to Make a Trace Fossil

Objective: To determine what information can be found from trace fossils. To determine the motion of a person from his/her tracks.

Materials Needed: paint (finger or tempura), long sheets of butcher paper, a walking cane, volunteers, other props

Preparation: Have some brave souls volunteer to get a little messy. Each volunteer will have a certain way of moving across the length of the butcher paper. Some possibilities include: walking, running, walking with a cane, limping skipping, hopping on one foot, cartwheeling, walking in pairs, etc. Each volunteer needs to remove shoes and socks and dip feet into paint until the bottoms are well-covered. On the butcher paper, each person has to go across the length in a particular way chosen so that a nice trail of feet tracks are laid down.

Lesson Body: Have other students try to come up with ways of determining how the tracks were made. What observations/evidence can they provide to support their guesses? (They are not allowed to ask direct questions to either the teacher or volunteers.)

Bring out actual examples of trace fossils (books, Internet, pictures, or actual fossils if possible). Have students make hypotheses as to what organism made them and what the organism was doing.

Wrap Up: Review the relevance of trace fossils to understanding past organisms. Relate how their process of thinking and questioning during "paint tracks activity" is similar to the approach used on actual trace fossils.