Solar System

Making a Fossil

What it does

This experiment shows how fossils are created.

What you need

• Paper plate
• Paper cup
• Plastic spoon
• Modeling clay
• Seashell or other object to imprint
• Petroleum jelly
• Plaster of Paris

What to do

1. Place a chunk of clay on the plate. Be sure it is bigger than the seashell you are imprinting.
2. Spread a thin layer of petroleum jelly on the outside of the seashell.
3. Press the seashell into the clay.
4. Carefully remove the seashell so that its imprint remains in the clay.
5. Mix 4 spoonfuls of plaster of Paris with 2 spoonfuls of water in the paper cup.
6. Pour this mixture into the imprint in the clay.
7. Wait about 15 minutes for the plaster to harden.
8. When the plaster is hard, carefully separate the clay from the plaster.

What it's all about

Both the clay and the plaster are types of fossils. In ancient times, living things made imprints in mud, which acted just like the clay in the experiment. This is called a cast fossil.

Sometimes sediments collect in the imprints, forming a sedimentary rock in the shape of the original organism. This rock is like the plaster in the experiment. This type of fossil is called a mold fossil.

Remember, be sure you have a parent, teacher, or other adult help you!

ASU geologist Jack Farmer finds cast fossils in the crystallized minerals of Mono Lake.
Read about it.