Student Data Sheet
Name _____________________
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 clay
Bottom 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 model
Plaster 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 an empty cavity termed a fossil mold. The mold has the detail of the
original fossil bone, 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.