Title:Formation of fossil molds and casts.
Description:Students will model in the lab, how fossil molds and fossil casts are formed.
Materials:Student lab sheet. ½ cup plaster of paris, plastic models of bones, teeth, and
sea shells, (plastic fossils kit),1 stick of modeling clay, 100 ml beaker, one stirring rod, scalpels or scissors, and a glue stick.
Time required: One half period for each part of lab. End of one class period and the beginning of next period is suggested. Plaster of paris must dry overnight.
Student background:Students should be familiar with the processes involved in the
formation of fossil molds and casts.
Notes to teacher:If the plaster of paris is too thin, the fossil casts produced will break apart as the student try to remove them from the clay. Clay must be soft for use in this lab.
Procedures: 1. Hand out worksheets and explain procedures and where material will be found.
2. Instruct students to label their materials for use the next day.
3. Allow students time to complete lab.
4. Summarize class results and ask students to make conclusions. (Data section).
Sample Scoring Guide
1. In the data-analysis section, each blank question is worth two points.
2. each sketch is worth five points.
Student Data SheetName ______
Period ______Score _____
Title:Formation of fossil molds and casts.
Purpose:In this lab activity, you will demonstrate how fossil molds and fossil casts are
formed.
Materials: ½ cup of plaster of paris per student, plastic models of sea shell, teeth, and small bones (plastic fossil kit), 1 stick of molding clay per student, 100 ml beaker, 1 stirring rod, scalpels or scissors, and glue sticks.
Procedures:
Day One......
1. Take the piece of clay and divide it into two equal pieces. Flatten each piece out like a pancake.
2. Pick out a plastic model of a fossil.
3. Place the fossil in between both pieces of clay and press down firmly from the top. As this is done, the bone, tooth, or sea shell will make deep impressions in the clay.
4. Pull the two pieces of clay apart and retrieve the plastic bone, tooth, or sea shell.
5. Fill in the information in Part A of the Data-Analysis section of the lab.
6. Fill you beaker approximately ½ full with plaster of paris. Add tap water slowly, while mixing, until the plaster of paris is the consistency of pancake batter.
7. Pour the plaster of paris into both fossil molds that you have previously made.
Fill each until they are level with the top of the clay.
8. Place your clay samples in the lab drawer, and allow to sit until the next day.
Day Two.
9. Remove your clay samples from the lab drawer.
10. Carefully remove the hardened plaster of paris from the clay. Cut off any jagged edges from the sides of both pieces.
11. Glue both pieces together.
12. Examine your hardened plaster of paris, and fill in the information on Part B on the data-analysis section.
Data-Analysis Section.
Part A.
1. After you removed the plastic bone, tooth, or sea shell from the clay, the deep impressions left behind in the clay, are examples of fossil ______.
2. In the boxes below, make sketches of both of your clay samples.
Top half of clayBottom half of clay
Bottom f
3. Upon examination of both the top and the bottom impressions in the clay, are they close to an exact replication of the original fossil model you pushed into the clay? ______
4. In nature, what originally happens to the real bone, tooth or sea shell that has been
buried in sediments? ______. What happens to the sediments over time? ______.
Part B.
5. The two pieces of plaster of paris that you glued together represent what type of fossil commonly found in fossil beds? ______
6. In the boxes below, make two sketches. One sketch is of the original plastic fossil model, while the other is your plaster of Paris cast.
Plastic modelPlaster of paris cast.
7. How closely does your plaster of paris cast, match the original plastic fossil you used? ______Explain______.
8. Using the information obtained while doing this lab, explain how fossil molds and casts form in nature.
A. Fossil molds
B. Fossil casts
Answers to questions in lab Activity.
Part A.
1. Fossil molds.
2. Sketches of top and bottom mold in clay.
3. Yes. (If student followed procedures).
4. A. Bone buried in sediments will dissolve away over time.
B. The sediments will turn to sedimentary rock.
Part B.
5. Yes (If students followed procedures).
6. Sketches of plastic fossil and plaster cast.
7. It matches if fairly closely. The detail is similar in both.
8. A. Bones, teeth, or sea shells are buried in sediments. With time, the sediments harden into sedimentary rock. The original fossil dissolves with time, leaving anempty cavity termed a fossil mold. The mold has the detail of the original fossilbone, tooth,
or sea shell.
B. If conditions are right, the fossil mold with fill with sediment. The sediment will
harden and create an image of the original fossil. This feature is termed a fossil cast and it will be a near copy of the original fossil.