Name Period
CHAPTER 4 ADDITIONAL INVESTIGATION C
Date
CHALLENGE
After you have completed the investigation on fossils, make a "fossil" mold and cast of a small, complete chicken bone. You can "copy" the work of a paleontologist by comparing the actual chicken bone to its fossilized cast.
PROCEDURE
Use the figure on page 115 in your textbook to help you make the mold and cast.
 Coat the bone very lightly with petroleum jelly or cooking oil. Press the bone very gently into modeling clay and use another piece of clay to cover the top of the
 bone. Carefully peel the clay away from the bone. Fill both halves of the fossil mold with plaster of paris. When the plaster begins to harden, join the two halves of the mold to make a fossil cast. When the cast is completely dry, carefully chip away any excess plaster.
Use a balance and the water displacement method to determine the density of the actual bone and the "fossilized" bone. First, use a balance to find the mass of the actual bone and the "fossilized" bone. Record the mass in Table 1. Then, find the volume of the bone and the "fossilized" bone. To find the volume, fill the graduated cylinder partway with water. Record the volume. Next, place the bone in the graduated cylinder and record the volume. The difference, or the change in volume, is the volume of the bone. Remember that 1 mL of water is equal to 1 cm
3 of water. Repeat for the "fossilized" bone. Record your results.
Table 1: Density of Actual Organic Matter vs Its Fossilized Cast
Actual Chicken Bone Fossilized Cast of the Chicken
Bone
Mass (g)
Volume (cm
3
)
Density (g/cm
3
)
Mineral composition calcite (calcium carbonate)
(density ~ 2.7 g/cm
3
) gypsum (plaster of Paris)
(density ~ 2.0 g/cm
3
)

While you can easily tell the real bone from the "fossil," it is not always easy for scientists who find actual bones and fossils. How might a paleontologist in the field use a method similar to what you did to determine if fossil bones are actual organic matter or fossil casts?

Sample answer: If scientists know the density of a particular kind of rock, they can find the density of the fossil to determine whether the fossil is rock or organic material. The densities of the fossil and the organic material would differ.
 Clean chicken bones by boiling them for about five minutes. Then soak the bones in a dilute solution of water and household bleach for about 20 minutes.
Thoroughly rinse the bones with fresh water and allow them to dry completely
(usually overnight) before distributing them to students.
 Make sure students determine the mass of the bone and its "fossilized" counterpart before they attempt to determine volume. Any water that is absorbed by either will affect students' calculations.
 If you wish, allow students to use calculators to facilitate their making computations.