Make a Model Fossil

Anne E. Flynn
St. Charles Borromeo School
St. Anthony Village
Based on an original activity from Harcourt Science 2006. Page 215
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In this investigative activity, students will gather materials from their outdoor environment and work individually (or in pairs) to create a model of a fossil using primarily modeling clay and glue. Students will form and discuss the differences between a "mold" and a "cast" model fossil(s).

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Learning Goals

This activity is to show, in a concrete way, the different ways fossils can be formed. Students will discover the unique qualities of both a "cast" and a "mold" fossil. They will learn two ways of making fossils. A mold fossil, the clay imprint, takes the shape of the natural object. The cast fossil is a reproduction of the natural object. These will also be key vocabulary words built into this lesson: fossil, model, cast, mold, imprint, reproduction (copy), and formation.
Along with these basic concepts and vocabulary, students will be asked guided, critical thinking skill questions and will be learn to interpret different visual models. Further investigation will occur when students are asked to discuss the differences and similarities of fossil models when compared to real fossils.

Context for Use

Developing a working model of a fossil is structured for third grade level students of an average class size of 15-25 participants. However, this lesson can also be used for individual learning, or students can be put into pairs or small groups. Expect to take 2 days/sessions. One day to create the models and the other to investigate the outcomes.
This classroom/outdoor activity will take approximately 30-40 minutes depending on class size, materials available, and whether or not the classroom instructor takes class time to have students go out into the field to search for materials, or provide them to the class. The 'fossils' (glue) will need a minimum of overnight/24 hours to become hardened before being handled/removed by students.

Subject: Geoscience:Paleontology
Resource Type: Activities:Classroom Activity, Lab Activity, Field Activity
Special Interest: Field-Based Teaching and Learning
Grade Level: Intermediate (3-5)
Theme: Teach the Earth:Enhancing your Teaching:Teaching in the Field, Teach the Earth:Course Topics:Paleontology

Description and Teaching Materials

This lesson should be used in conjunction with discussion of Earth Science, rocks and minerals, types of rocks, etc. This lesson was designed to explain and answer the question, "What are fossils?" This lesson will also teach students how scientists use models to explain and help them to understand a physical representation of a structure or a process. Be sure to remind students prior to beginning this lesson of the factor of "time" that is not being represented during this investigation. Fossils form over millions of years...not overnight as these models will.


-Seashell (or other 'once-living,' natural material such as leaves, twigs, flower, etc.)
-Small plastic bowl
-Petroleum jelly
-White glue (not glue stick)
-Modeling clay


Coat outside of object with layer of petroleum jelly

2. Press the object into the clay to make a model
3. Remove object carefully from clay
4. Place the clay with the object's shape into the plastic bowl.
5. Slowly pour/drizzle white glue into the imprint. Fill it completely. This will also make a model of a fossil.
6. Let the glue harden (at minimum) overnight. When hardened, carefully separate the formed glue from the clay.

Answer questions from Investigate worksheet and then conclude lesson with having students compare/contrast their model with real fossils.

This activity is fully documented in the Harcourt Science, 2006 Teacher Edition on pgs. 214-221.

More source information and complete references can be found by going to the Harcourt Science website:

Teaching Notes and Tips

This activity is taken completely from Harcourt Science, 2006 as part of a comprehensive earth science curriculum. Within the teaching manual, many of the concepts and expected outcomes of this activity are covered more thoroughly. The only real change from within the Harcourt activity will be taking students out into their environment and having them select the 'natural' object that they will use to create their fossil model(s). The Harcourt version requires and provides for use of seashells during this project. Living in Minnesota, I believe these items should be more relevant to where the students live; so twigs, leaves, acorns, flowers, and other native-to-Minnesota items should be selected. This is a terrific method to clarify the differences between a cast and a mold. The concept of "deep time" is difficult to get across to the students. Use of analogies and a visual time line or a "living" time line (where students stand in various positions along a line in a long hallway or outdoors on a playground) to show how long it takes fossils to actually form, would be helpful as a pre-activity to this lesson.
Students may need to be reminded while searching for their objects about the differences between (once) living things and non-living things. For example, often students will select a rock, or a bottle cap, to use to create their fossil. Rocks cannot be used because they are non-living objects, etc.


Students will show their knowledge of the difference between a cast and a mold fossil by completing a written assessment tool. Performance assessment can be made of students' individual work of creating a visible model of their fossil and will be asked (orally) to explain which model represents a mold and which a cast.
Further assessment will be made by instructor observations during the fossil model selection and formation processes.
Students will have the opportunity to complete a self-assessment by reflecting on their work and completing a checklist of their progress during the lab. Students may also work in pairs of groups to check each others work/outcomes.


3.I.B.1-3 Questioning natural world, participation using appropriate tools (model), and differentiating kind of investigation depending on questions being answered.

References and Resources