Homemade Fossils

What You Need:

• photographs of real fossils, from books or from the Internet
• large piece of recycled cardboard, plastic tarp (or other disposable work surface)
• modeling clay or play dough (homemade or store-bought)
• waxed paper
• small objects to turn into "fossils": seashells, fresh leaves, small plastic dinosaurs
• vegetable oil and brush (or non-stick cooking spray)
• plaster of Paris
• plastic mixing container that can be thrown out
• water
• plastic spoon

What to Do:

1. Ask your child if she knows how long ago dinosaurs like Tyrannosaurus rex and Triceratops lived. After considering some answers, explain that these animals lived a long, LONG time ago — millions of years ago — before there were any people around. Many children are surprised to learn that no person — not even cavemen ever saw a dinosaur. So, how do we know these large animals once lived on our planet? Answer: When these animals died, they left behind clues known as fossils. Your child may have heard the word fossil before, and some might have some idea of what they look like, but probably isn't sure of what fossils really are.
2. Show a photograph of a fossil. Explain that fossils are stones that look like plants or animals that lived long ago. When most living things die in the wild, some other animals survive by eating the dead animal's remains. But sometimes, rarely, when a plant or animal dies, and gets covered with mud, sand or soil. Over long periods of time (millions of years), the animals' bones turn into stone.
3. Show your child a video clip from "Fossil Fred" (above). Afterward, ask your child to discuss how fossils are made.
4. Tell your child that even though real fossils usually take millions of years to form—he is going to make models of homemade fossils in just one day.
5. Working on a large disposable work surface (cardboard or plastic), have your child press and roll around a large ball of clay or play dough on a large piece of waxed paper. The goal is to make the ball as smooth as possible.
6. Press some small objects (bones, shells etc.) deep into the surface of the clay or play dough. Then remove them to see their impressions.
7. If working with play dough instead of clay, let it dry overnight. If working with clay, continue to the next step.
8. Brush a small amount of vegetable oil into each impression (or apply small amount of cooking spray).
9. Prepare a batch of plaster of Paris according to the package directions. The goal is to make it smooth but thick. Help your child spoon the plaster into each impression until it is filled.
10. Wait about 30–60 minutes for the plaster to dry completely. Then peel away the clay or play dough to reveal the fossil.
11. IMPORTANT: For clean up, throw out the container used to mix the plaster. Do NOT rinse this container in the sink, as it can cause plaster to set in the pipes.

Extensions:

• To give your child the experience of excavating (digging out and removing) fossils from stone, they can first "bury" some bones and shells in a batch of plaster of Paris that is then allowed to harden inside a disposable container such as an old milk carton. Your child then can use simple (non–sharp) tools to scrape away the plaster until the hidden objects are revealed.
• Older children can use chicken bones to create complete skeletons. Use photographs of real fossil skeletons as a model.