Fossil Casts, Molds, and Impressions

Want to explore fossils in a hands-on way but can’t break the bank with casts? Teach your students how to make their own fossil casts! These fossil casts, molds, and impressions use white glue to create these fun hands-on fossils.

This easy guide comes from the Kentucky Geological Survey so check out their post for more details!

Grades: 3-5

Introduction to the Activity

Kentucky Geological Survey

This activity gives you a great way to create “fossil” molds without using messy plaster. Here you can use white glue to demonstrate the processes that are used to create real fossil casts and molds every day.

The activity provided in the link says that the activity is appropriate for grades K-8, but I personally think this activity is best suited for grades 3-5. But don’t let that stop you if you want to do this activity with 8th graders.

Conceptual Background

Fossils are natural preservations that give scientists insight to the ecology and structures of ancient organisms. Fossils form over the process of millions of years and can only form under certain conditions. There are two common kinds of fossils that paleontologists encounter: body fossils and trace fossils. A body fossil is an exact replica of a living organism, and is what you often see in natural history museums. Trace fossils are like a footprint, and are often found in the form of tracks, trails, and burrows. In order for a fossil to form, an organism had to have been buried under a layer of sediment. When the organism slowly decomposes, the sediment hardens and leaves a hollow space to be filled with different material, like rock. If water filters through the sediment as the organism decomposes, it will leave behind a perfect impression, creating an external imprint.

Museums will most often display plaster casts of fossils in order to preserve and study the originals. In order to make these casts, scientists use plaster of Paris, fiberglass, clay, or other similar materials in order to create a perfect impression of a fossil. First, the mold needs to be formed that will be filled with materials. Once the mold is formed, liquid polyester or other materials are used to fill the mold and create a replica of the original.

NGSS Connections

Analyze and interpret data from fossils to provide evidence of the organisms and the environments in which they lived long ago.

Disciplinary Core Ideas

LS4.A: Evidence of Common Ancestry and Diversity

  • Some kinds of plants and animals that once lived on Earth are no longer found anywhere. (Note: moved from K-2)
  • Fossils provide evidence about the types of organisms that lived long ago and also about the nature of their environments.

 

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