August Moment of Science:
Impression Fossils

play-dough-bug-imprints-for-preschool-Put on your paleontology hat and get ready to make some fossils during this month’s Moment of Science! Scientists categorize fossils into three main groups –  impression fossils, trace fossils, and replacement fossils. Fossils are bits of plants or animals that have been preserved from the past. There are three types of fossils based on how they are formed. The three types of fossils are:

1. Impression Fossils
These fossils contain prints, or impressions, of plants or animals from long ago. The plant or animal lands in mud, silt, or sand and makes an impression. Over time, it disappears, but the impression remains. The mud, silt, or sand hardens into rock, and an impression fossil remains.

2. Trace Fossils
These types of fossils capture the activities of ancient animals. The animals leave its footprints or scat, which makes an impression in the soft mud, silt, or sand. Just like impression fossils, the soil hardens to form rock, preserving a trace of the animal.

3. Replacement Fossils
These fossils are replicas of things that were once alive, such as trees or sea creatures. These living things are trapped, die, and are covered by mineral-rich water. As they rot, the organic parts are replaced by a hard mineral called silica. The minerals fill in the spaces and create a replacement, or replica, fossil of the living thing.

Now that you know about the different fossils, it’s time to make your own!

playdough-bug-printing-First, gather your materials:
1 cutting board
Plastic dinosaurs/insect toys (the more detail the better!)


  1. Flatten Playdough into small disks or squares, large enough to fit one of the plastic figures or plants you will be fossilize
  2. Firmly press dinosaur/insect figures into the Playdough (you can press your figurine sideways, on its feet/hands, etc.)
  3. Carefully remove plastic figure to preserve the imprint
  4. Repeat steps 1-3 with a different figure or from a different angle

As each fossil is imprinting talk to your paleontologist about the fossil they are making. Which fossil are they creating, an impression fossil or a trace fossil? If they were looking for fossils, how could they use different parts of the imprint to identify what animal had been there? Can they think of anything else that could turn into a fossil? Try gathering leaves, plants, and flowers from the backyard and see how each one creates a different impression. Once they’ve created multiple fossils, can they pair up the original animal/plant to the fossil? Share photos of your experiment with us on social media by tagging @discoverycubeOC and @discoverycubela.

Don’t miss the Extreme Dinosaurs exhibit now open through September 5, 2016 at Discovery Cube OC to see real and replica fossils on display!

This blog post was inspired by and features images from