Fake Fossil Casts
We can’t make a real fossil, because that would take millions of years and special conditions but we can make our own fake fossil casts.
Plaster of Paris is made from a rock material called "gypsum". It’s a special material that doctors once used to make casts when people broke their arms and legs. The strangest thing happens to plaster of paris when it begins drying. Do you know what that is? It gets hotter when it begins to dry. This is called an "exothermic" reaction.
Give each child a small disposable cup with his or her name on it that is ¼ full of sand. Have each child choose an item to fossilize – a leaf, a shell, the cleaned bones of a small fish, a chicken bone, or anything they want to bring in. Generously coat the object with petroleum jelly. Have the children place their items, bumpy side up, on the sand. Have paper towels or rags handy.
Make the plaster of paris. Pour the plaster of paris into the cups. Let the cups harden (one half hour to one hour). When hard, invert the cup over a waste can and remove the item from the plaster.