Fossil Preservation

This activity is from Step by Step Experiments in Earth Science by Janice Van Cleave


How were fossils preserved? This hands on experiment models the process.

Supplies Needed

  • paper plate

  • paper cup

  • modeling clay

  • seashell or other item

  • petroleum jelly

  • plaster of Paris

  • plastic spoon


  1. Place a piece of clay about the size of a lemon on the paper plate.

  2. Rub the outside of the seashell or item with petroleum jelly.

  3. Press the seashell or item into the clay.

  4. Remove the item and make sure a clear imprint of it remains in the clay.

  5. Mix four spoonfuls of plaster of Paris with two spoonfuls of water in the paper cup.

  6. Pour the plaster mixture into the imprint in the clay. Throw the spoon and cup away.

  7. Allow the plaster to harden for 15-20 minutes.

  8. Separate the clay from the plaster mold. Now you have a fossil!


How it Works

The layer of clay and the plaster are both examples of fossils. The clay represents the soft mud of ancient times. Organisms (living things) made imprints in the mud. If nothing collected in the prints, the mud dried, forming what is now called a cast fossil. When sediments filled the imprint, a sedimentary rock formed with the print of the organism on the outside. This type of fossil is called a mold fossil.