Fossils: Cast and Mold Discovery Investigation
Learning Goals:
Students will:
1. Recognize that distinctive definitions on fossils make them easier to
discover
2. Draw the plaster layers they created and understand the difference
between a cast and a mold and that these layers represent layers of
the earth
3. Define what a fossil is
4. Explain how fossils provide evidence of prehistoric life
Day 1
Materials Needed:
 Half pint milk cartons
 Craft sticks for stirring
 Food coloring
 Plaster of paris
 Newspapers
 Fossil objects
 1 clear cup
 ½ cup
 Tablespoon
 Water
 Baby powder
Instructions:
1. Spread newspapers over group work area
2. In a milk carton, add ½ cup plaster of paris and 4 tbsp. water.
3. Stir with craft stick until smooth.
4. Let it sit for ONLY 5 minutes.
5. While you wait, answer questions in your journal.
6. At 5 minutes, sprinkle baby powder into the milk carton.
7. Gently press your “fossil” onto the powder and plaster.
8. Sprinkle more powder on the “fossil object” until it is covered.
9. Mix ½ cup of plaster with 4 tbsp. of water and a few drops of
food coloring in the clear cup.
10. Pour it over the mixture in the milk carton.
11. Set the carton in a safe place to dry.
12. Finish day 1 questions in your journal.
Day 1 Questions:
1. Draw and describe how you set up your fossil.
2. Why did we add baby powder and food coloring to our fossils?
3. What do you think will happen tomorrow when we break open our
fossils?
4. How is your fossil like a sedimentary rock?
Day 2: Fossil: Cast/Mold Investigation
Materials:
 Small hammer
 Nail
 Soft paint brush
 Newspapers
 Safety goggles
1. Instructions:
Tear the milk carton off of the plaster.
2. Put on safety goggles.
3. Hold your nail on the side of the plaster between the two
layers and gently tap with the hammer.
4. Use a soft, dry paint brush if necessary to clear out any extra
baby powder.
5. Complete the questions.
Questions:
1. Draw in detail what your fossil looks like now.
2. How are fossils formed?
3. Are all fossils discovered and how is this like paleontologists that
are excavating a real fossil?
4. Why is the discovery of fossils important?
5. What are you wondering about fossils now?
6. Which part of your fossil is the cast and which part is the mold?