7. Choose Your Own Fossil Adventure

Fossils are extremely rare but also extremely exciting and rich with information about past life on Earth. In this lesson, students learn about the major types of fossils and how they form. They complete the lesson by illustrating and creating a “Choose Your Own Adventure” type story in which a Tyrannosaurus rex dies with 7 different possible endings, only one of which results in the discovery of its fossilized skeleton.

T rex

Can list the different types of fossils and the way each forms.
Can describe and diagram the conditions required for the formation and discovery of fossils.
Can understand why fossils are so rare and why many forms of life that once existed on Earth have not yet, and may never be, discovered.

Body fossils
Trace fossils
Mold fossils
Cast fossils

Attachment Size
fossil_adventure_pages.doc 34.5 KB
7fossil_adventure_v2.doc 63 KB

7. Fossil Adventure - Logistics

20 minute class discussion on the types of fossils and how they form
30 minutes create the Choose Your Own Fossil Adventure book



  • Pictures of different types of fossils (see sources for some recommendations of great websites if you don’t have access to books on fossils)
  • Copy of Choose Your Own Fossil Adventure pages
  • Scissors
  • Stapler
  • Optional: 8.5 X 11 paper
  • Optional: colored pencils or markers
  • Optional: a chunk of modeling clay or Playdoh


7. Fossil Adventure - Background

Teacher Background
No exploration of the geologic time scale is complete without thinking about fossils. Fortunately, kids love fossils. However, there are many common misconceptions – that fossils are fairly common, that every species that once lived must have been preserved in some way, that fossilized skeletons are often found intact. What students rarely understand is that fossils are extraordinarily rare. In fact, the vast majority of species that once lived on the planet vanished without a trace. Each and every fossil is precious because there are so few of them and because each fossil can provide so much information about past life on this planet.

Fossils are the preserved remains of former life or traces of them such as molds, casts, and footprints. The main categories of fossils include:

  • Body fossils – mineralized or preserved remains of body parts such as teeth, shells, bones or claws. The most common way body fossils form is by an organism being covered in sediment soon after death. The sediment provides a shield from damage by scavengers, weathering, and decay. The amount of time that passes before the organism is covered determines how much is eventually fossilized – if covered quickly by a sandstorm or landslide, an entire skeleton and even scales or hair may remain, whereas if covered slowly, only the most easily preserved hard tissue such as teeth may remain. As the layers of sediment build over thousands of years, the sediment layers become rock through compaction and cementation. At the same time, the remains of the organism decays and is slowly replaced with minerals that seep through the sedimentary rock, such as calcite, silica, and iron. This process by which body parts are replaced with rock is called permineralization. Different tissues are permineralized at different rates so even the internal details of bones and teeth may be preserved. In addition to permineralization, an animal or plant may become preserved in tar (the La Brea Tar Pits), in ice (several wooly mammoths have been discovered encased in Siberian ice), or in amber (insects are commonly preserved in amber).
  • Trace fossils – fossilized evidence of the behavior of past life such as footprints, nests, burrows, eggs, and droppings. Trace fossils are extremely precious because they provide information about the lifestyle and behavior of past life. Do they take care of their young? Do they live singly or in groups? How do they walk? Where do they live?
  • Mold fossils – a negative imprint of an organism preserved in stone. While the organism itself may decay without being preserved, the imprint remains in the sedimentary layers that eventually become sedimentary rock.
  • Cast fossils – a positive imprint of an organism preserved in stone. If a mold fossil is filled in with additional sediment, this second layer becomes a cast fossil.

Due to the rarity of fossils, the buying and selling of fossils has become a highly controversial subject. Paleontologists are concerned that the commercial fossil trade is harmful to science. Scientists fear that if unique fossils with great scientific importance are purchased by private collectors, then these finds may not be available for scientists to study. On the other hand, private collectors insist that most fossils are being made available to researchers and many are ultimately donated to museums. For a great video discussing the subject, see “Curse of T Rex”, a 1997 Nova special about the discovery of an astonishingly complete T rex skeleton (Sue, now on display at the Field Museum (http://www.fieldmuseum.org/SUE/)) and the battle that ensued between scientists, commercial fossil hunters, the US government, and property owners.

Student Prerequisites
A good understanding of how sedimentary rocks form and of basic stratigraphy principles. Knowledge of the geologic time scale is helpful but not required.

7. Fossil Adventure - Getting Ready

Getting Ready

  1. Find good fossil pictures in each of the 4 categories to show students (body fossil, trace fossil, mold/cast fossil)
  2. Make copies of the Choose Your Own Fossil Adventure handout
  3. Set out scissors, staplers, and colored pencils for students to share

7. Fossil Adventure - Lesson Plan

Lesson Plan

  1. Have students write down on a piece of paper: what they know about fossils and what questions they have about fossils.
  2. Spend 5 minutes allowing students to share what they know and the questions they have. You may want to write up some of their questions and knowledge on the board.
  3. Summarize their responses into a general definition of “fossil” – the preserved remains of past life on earth or traces of their existence. Students may write this definition in their notes.
  4. Next, tell students about the different types of fossils that might form: body, trace, mold, and cast fossils. As you describe each type, show students pictures of fossils and describe how each are formed. This is also an opportunity to review how sedimentary rocks form and the similarities between sedimentary rock formation and permineralization. You can model the formation of cast and mold fossils using clay or Playdoh (make an imprint of your hand in clay or Playdoh and discuss how part of a plant or animal might create an imprint in mud or sediment).
  5. Discuss what different kinds of information one might learn from body fossils such as a bone, trace fossils such as footprints or a nest, and mold/cast fossils such as plants. Throughout this discussion answer relevant questions from the students’ list.
  6. Close this introductory portion by reviewing the process of permineralization and point out all the ways this process could be set off course – decomposed by bacteria, destroyed by scavengers, weathered to dust, crushed by too many layers of sediment, uncovered before fossilization, destroyed by earth forces, never uncovered by erosion, uncovered by erosion but washed away or eroded before being discovered, etc.
  7. Finally, tell students that they will now put together a “choose your own adventure story” about fossil formation. A T rex has died and many things can happen to the carcass, only one of which leads to becoming a fossil. To make a very simple book, students should cut out each page of the story, assemble it by the page numbers at the bottom of each page, and then staple the pages together. If you want your students to illustrate the book, they can draw a picture on the back of the page before. Alternatively, take 3 sheets of regular 8.5 X 11 paper and fold them in half “hamburger-style.” The text for each page can be cut from the templates and pasted on the pages of your booklet. The remaining portion of each page can be used for illustration. For an even greater challenge, have students add their own “extra credit” pages with additional scenarios for their T rex skeleton. Students can have the rest of the class period to create their books.

7. Fossil Adventure - Assessment


  1. As homework, I had my students share their book with someone else that didn’t take my class: a parent, sibling, or friend. They had to read the story to this person until he or she discovered the path to making a fossil and discovery by a scientist. My students also had to answer any questions their “someone else” had about fossils.
  2. Have students create a flow chart describing the process of permineralization.
  3. Have students put describing the steps in fossil formation in the correct order:

    ____    minerals in the ground water crystallize within the tiny crevices left behind as the muscle and bones decompose, slowly replacing the bones, teeth and claws with rock, turning the T rex into a fossil
    ____    a T rex dies near the edge of a river
    ____    T rex’s body gets covered in sediment and is protected from scavengers and from being destroyed by the weather
    ____    as millions of years pass, the layers of sedimentary rock that once surrounded the now fossilized T rex erode away
    ____    minerals in the ground water cement the sediment together to form sedimentary rock
    ____    a paleontologist discovers the fossils!

  4. Have students explain in a paragraph why most of the past life on Earth vanished without a trace.

Going Further

  1. Make your own fossils and have your students excavate them! Carol Mankiewicz and Carl V. Mendelson from Beloit College describe how to make trace fossils with plaster of paris and the footprints of a small classroom pet. Paul Belmas of Bannach Elementary describes how to make body fossils from chicken bones, sharks teeth, or other animal remains with plaster of paris and sand. Roger Evans creates a field trip experience with buried animal bones in an outdoor site.
  2. Study a specific fossil (or set of fossils) in detail, drawing connections to the geologic time scale and stratigraphy. One fantastic lesson of many is the in depth study of the Laetoli footprints with this lesson by Steve Randak. These footprints offer indisputable evidence that by 3.6 million years ago, our human ancestors were walking on 2 legs. Students can study these footprints to investigate the height, stride length and walking speed of our ancient ancestors.

7. Fossil Adventure - Sources and Standards

This lesson was adapted from the “Fossil Finding” lesson by the Museum of the Rockies by including multiple possible endings besides the formation and discovery of a fossil. This and other excellent lessons may be downloaded from their website.

Another great explanation of how fossils form, with good pictures, can be found on the Discovering Fossils website.

Other great K-12 paleontology lessons may be found at:

  • Paleontological Experiences for Science Teachers by the University of Wisconsin
  • Learning from the Fossil Record by the UC Museum of Paleontology
  • Earth Science Classroom Activities from the Kentucky Geological Survey

For pictures of fossils, see:

  • The UC Museum of Paleontology’s online collections
  • The Smithsonian Institute’s online resources on Evolution and Paleontology
  • The Royal Tyrell Museum has great information about its exhibits

Grade 7
Earth and Life History (Earth Sciences)
Evidence from rocks allows us to understand the evolution of life on Earth. As a basis for understanding this concept:
a.    Students know Earth processes today are similar to those that occurred in the past and slow geologic processes have large cumulative effects over long periods of time.
e.    Students know fossils provide evidence of how life and environmental conditions have changed.
g.    Students know how to explain significant developments and extinctions of plant and animal life on the geologic time scale.