Lesson Plan

Make Your Own Fossils

Dried "coffee fossils" showing impressions of long sprigs of grass.
Grade Level:
Upper Elementary: Third Grade through Fifth Grade
Lesson Duration:
60 Minutes
State Standards:
Colorado Academic Standards for Science: 4th grade 2.2.a – Explain what fossils say, the similarities between fossil and living organisms. 2.2.b – Interpret evidence for past environments.
Thinking Skills:
Understanding: Understand the main idea of material heard, viewed, or read. Interpret or summarize the ideas in own words. Creating: Bring together parts (elements, compounds) of knowledge to form a whole and build relationships for NEW situations.

Essential Question

How are fossils made?


Students will learn to make the distinction between different fossil types. Students will also learn about the process of carbonization


Fossils are the remains of once living things and provide evidence to what past environments were probably like. Fossils are also useful in helping scientists to distinguish periods of geologic time. Without the presence of fossils in rock, it can be much more difficult to make inferences of what took place in the past.
How do fossils form? There are a variety of ways that fossils form and it usually depends on the characteristics of the organism. Some of the more common fossilization types are: 1) molds and casts, 2) permineralization, 3) replacement, 4) compressions, 5) trace fossils, and 6) freezing. In molds and casts, sediment deposits fill in the cavities of the organism and produce a 3D model. In the permineralization process, the organic matter (carbon) decays and is replaced by a mineral (e.g., silica) while retaining the most of the information of the organism. Replacement is when the organic matter decays and is completely replaced by mineral(s) leaving little to no information of the organism. Compressions are two-dimensional fossils that retain the organic matter of the organism. Trace fossils form when an organism moves over the surface of soft sediment (e.g., tracks), leaves excrement/vomit behind, coprolite/regurgitalite (e.g., feces/vomit). Although rare, freezing can produce fossils that preserve even internal organs (e.g., mammoths uncovered in permafrost).
At Florissant Fossil Beds National Monument, the delicate insects and plants that lived in Florissant valley during the Eocene are preserved as carbon compressions. Essentially, as the organisms decomposed, they left behind a thin carbon film of the original organism. This process is known as carbonization. We can think of this thin carbon film as a micro-cast of the organism. In some cases, sturdy plants, insects and mollusks (e.g., clams and snails) were hard enough to leave an impression behind in addition to the thin carbon film. On the other hand, the giant redwoods of Florissant valley were preserved as permineralized fossils. Lahars that covered the lowermost portions of the redwoods provide enough silica that eventually replaced the organic material of the trees. We also find trace fossils of organisms at Florissant Fossil Beds, such as bird tracks, regurgitalite (vomit) of fish and coprolite (feces).


You will need:

  • A large bowl

  • Spoon

  • Wax paper or foil

  • 1 cup of flour

  • ½ cup of salt

  • 1 cups of cold coffee or water

  • 1 cup of used coffee grounds (optional)

  • Leaves, sticks, etc. you want to make fossils of

  • Paint (optional)

Lesson Hook/Preview

Fossils are the remains of once living things and give scientists evidence of what environments were once like when those organisms were alive. Fossils are also helpful to scientists trying to distinguish periods of geologic time.


#1: Go over background information with the student(s).
There are a variety of ways that fossils can form that often depend on the characteristics of the organism. Some common types of fossilization include: molds and casts, permineralization, replacement, compression, trace fossils, and freezing.
In mold and cast fossils, sediment fills in the cavities of an organism producing a 3D model of it. In permineralization the organic material (such as carbon) is replaced by a mineral while retaining most of the information about the organism. The petrified redwood stumps at Florissant Fossil Beds National Monument were formed by permineralization. Volcanic mudflows called lahars had covered the bottoms of the redwood trees and provided enough silica that replaced the organic material of the wood.
Replacement is when the organic matter decays and is completely replaced by minerals. This leaves very little information about the original organism behind. Trace fossils are not usually an organism but are evidence that an organism had been there while it was still alive. Trace fossils include things such as tracks and footprints, and feces or vomit. There are some trace fossils found at Florissant Fossil Beds such as bird tracks and a coprolite (feces) and regugitite (vomit) from fish.
Fossils formed by freezing are more rare. But they can preserve even the internal organs normally lost in other fossils. Freezing has fossilized mammoths! Some even have hair still left!
#2: In the bowl mix 1 cup of flour and 1/2 cup of salt. Add 1 cup of used coffee grounds. Hint: Let the grounds dry out first or use a bit less liquid liquid later.
#3: Add 1 cup of cold coffee or water and mix well to create your "sediment".
During the Eocene there were many different organisms living in the Florissant Valley. The delicate plant and insect fossils in Florissant Fossil Beds National Monument were formed by compression. The plants and insects would fall into the ancient Lake Florissant and settle to the bottom. As the organisms were buried, more sediment was deposited on top and squished them.
#4: Lay out your leaves and sticks on a sheet of wax paper or tin foil. Make sure there is a bit of space between them all.
#5: Cover your leaves and sticks in the "sediment" mixture you made. It might help to use the spoon to spread it over them bit by bit. Leave some space as you do this to create separate fossils, or you'll get a huge sheet!
#6: Let your fossils dry completely. You can leave them in a window to let the sunlight help.
As the organisms decomposed they left behind a thin carbon film resulting in a dark stain from the organism. This is called carbonization. The carbon films can be thought of as a micro-cast of the organisms. Some of the more sturdy plants, insects, and even mollusks (such as snails or clams) were hard enough to leave behind an impression along with a carbon film.
#7: When your fossils are completely dry, flip them over and carefully remove the remaining leaves and sticks. You should be left with an imprint of them in your new fossils.
#8 (optional): If you want, you can use brown or tan paint to color the imprints of your fossils to look like carbon left behind by the leaves.


  • Fossil: noun; a trace or print or the remains of a plant or animal of a past age preserved in earth or rock

  • Cast: noun; the sediment that fills in a mold and takes the shape of the original organism

  • Mold: noun; the frame in which something is constructed or shaped; the sediment that formed around the organism and remains after the organism decays away retaining its form

  • Compression: noun; the act, process, or result of becoming pressed together or reduced in size, amount, or volume by pressure

  • Permineralization: noun; in which minerals are deposited by water and form internal casts of organisms by filling in the spaces inside the organic materials

  • Replacement: noun; the act of new minerals taking the place of the original materials or minerals

  • Trace Fossil: noun; the fossil of a footprint, trail, burrow, or other evidence left by a past organism while it was living

  • Carbonization: noun; the process of being changed into or becoming carbon

  • Regurgitalite: noun; fossilized vomit

  • Coprolite: noun; fossilized feces

  • Freezing: verb; to harden into or be hardened into a solid by the loss of heat; to become fixed or motionless

Assessment Materials


Review the different fossilization types.
Why aren't the trunks of the giant redwoods (Sequoia affinis) of the Eocene Florissant valley preserved as compressions?
Do you think the Palaeovespa florissantia (an ancient wasp) was hard enough to leave an impression in the shale? What about a compression? Why or why not?

Rubric/Answer Key

The trunks were sturdy and large enough to be permineralized by the minerals in the lahar that buried them.
The Palaeovespa florissantia wasp was too soft to leave an impression. But a compression fossil was formed as the carbon of the organism was preserved.

Additional Resources

Check out our other Make Your Own Fossils activity webpage for step by step instructions with pictures!

Contact Information

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Last updated: August 16, 2022