Lesson Plan

A Fossil’s Journey

three dog skulls placed in a row
Grade Level:
Upper Elementary: Third Grade through Fifth Grade
Lesson Duration:
60 Minutes
Additional Standards:
3rd Grade:  3-LS4-1, 3-LS4-2, and 3-LS4-3
Thinking Skills:
Understanding: Understand the main idea of material heard, viewed, or read. Interpret or summarize the ideas in own words. Applying: Apply an abstract idea in a concrete situation to solve a problem or relate it to a prior experience.

Essential Question

1.  What is a fossil? 
2.  Are fossils rare? 
3.  Why are fossils important?


1.  Identify fossils and how they are formed.
2.  Distinguish between trace fossils and mere impressions.
3.  Recognize that because some plants’ and animals’ parts fossilize better than others this creates missing information in the fossil record.


Definition of a Fossil

A fossil can be defined as any naturally occurring evidence of past life. Fossils need not be mineralized (turned to rock) or even enclosed in rock. Many relatively young (10,000+ years old) Ice Age sedimentary deposits are un-cemented sand and gravel, but rich with true fossils. Ice Age mammoths that have been found preserved in permafrost are fossils, although their flesh is still mostly un-decayed. Ten thousand years is a lower limit often used for the age of organic remains that are considered fossils. There are three basic types of rocks: sedimentary, metamorphic, and igneous. With few exceptions, fossils occur in sediments or sedimentary rocks. Occasionally living things are preserved in lava flows or volcanic tuff deposits (igneous rocks), but these are relatively rare. Some metamorphic rocks (rocks changed by heat and pressure) contain fossils, but usually metamorphism destroys fossil details.  

The fossilization process is intimately connected with sedimentary processes. Thus, environments where sediments are being deposited (depositional settings) are places where plants and animals have the potential to be fossilized. Examples of depositional environments include a lake bottom, a river sandbar, a beach, ocean floor, or dune field. Sediments originate from a variety of different sources. Some sediments result from the breakdown, through weathering, of pre-existing rocks; these are called clastic sediments. Common clastic sediments are sand, gravel, silt, clay, and mud. The sedimentary rocks they turn into are sandstone, conglomerate, siltstone, claystone, and mudstone, respectively.  
Organic sediments originate as tissues of plants or animals. Leaf litter on a forest floor is an example of organic sediment. Much sand and mud in marine environments results from the break-down of shells or skeletons of animals (oysters and corals, for example) and plants (marine algae). This sediment is rich in calcium carbonate and forms the rock limestone. The organic sediment peat, usually deposited in a swampy environment, becomes, with heat and pressure, the sedimentary rock coal. Still other kinds of sediment are formed when certain chemicals in a body of water reach too high a concentration to remain in solution and precipitate out. An example is the evaporation of seawater to form salt. Some limestones also form this way.  


Regardless of the type of sediment or sedimentary environment in which an organism dies, fossilization is by no means guaranteed. There are several requirements that must be met before preservation of organic remains is assured. The difficulty of meeting all of these requirements is the reason that fossilization is a rare and chance occurrence. First, organisms that possess hard parts of some kind, such as bones, teeth or shells, stand a far better chance of fossilization than those that do not. Soft-bodied worms, for example, are extremely rare as fossils although they are common in marine and terrestrial settings. Absence of organisms with hard parts is the main reason that fossils from Precambrian time are so rare. The second requirement for fossilization is rapid burial in a protective medium. Upon death, the remains of most organisms are quickly acted on by scavengers and by microorganisms that promote decay. Physical action in the natural environment (e.g., currents, waves, wind, and rain) is also destructive. If the remains are to make it into the fossil record, they must be buried quickly in an oxygen-free environment before these processes have a chance to destroy them. The type of sediment also affects the quality of fossil preservation; fine-grained sediments are more likely to favor the preservation of small details.  
Examples of different kinds of fossilization include fish sinking to oxygen-free bottom of lake then buried in soft mud, herd of animals drowning in flood then buried in river sand, shell debris accumulating accumulates slowly on ocean floor, and animals grazing on plains which are then buried by sudden eruption of volcanic ash.

Conditions after burial are also important in aiding or hindering preservation of organic remains. This third stage in the process of fossilization is called diagenesis. Diagenesis refers to everything that happens to sediment after it is deposited. The effects of pressure, heat, and circulating fluids, that in time turn sediment into a sedimentary rock, also act on the organic contents of the sediment, altering their composition and appearance. Sometimes a potential fossil may be dissolved in the process of diagenesis. Other times it may become mineralized. Think of how hard water acts in a teapot or in water pipes overtime; deposition of minerals in those places is like the mineralization process that cements sediments into rock. Mineralization or petrification, a process in which a fossil effectively "turns to stone," may help preserve a fossil, but is not a requirement for fossilization. Many organic remains can be preserved essentially unaltered for millions of years and still be true fossils.  

Trace Fossils
Not all fossils are actual remains of living things. Sometimes only an impression of the animal or plant is left behind after its death, such as a natural mold of a shell. A trace fossil is evidence of some activity or behavior of an animal or plant while the organism was still alive. Some examples of trace fossils are footprints, burrows, coprolites, and root casts. Ancient ripple marks, mud cracks, or raindrops preserved in rock are called "sedimentary structures," but because they do not represent activities of living things, they are not trace fossils. Because actual remains of the organism that made a trace fossil are usually not preserved, the trace maker is often unknown.  Trace fossils are nevertheless strong and valuable evidence that certain kinds of activities occurred in a given environment. They are useful in learning about the types of animals and their interactions in ancient environments.   

Finding Fossils
How do paleontologists find fossils? The best way to find fossils is to look for them. Paleontologists often spend many days searching the ground for small fragments of fossilized shell or bone that might indicate that something worth digging up lies beneath. Fossils are not found everywhere, so scientists must use clues to help them narrow their search. The best way to start is by studying a geologic map. A geologic map shows the age and type of rocks at the surface. This method works because paleontologists generally know the age of fossils they want to find and whether they lived in a marine (saltwater) or non-marine (freshwater or dry land) environment. Studying a geologic map will often allow a paleontologist to narrow the search down to a few square miles.  
Two other factors that are important in deciding where to look for fossils are how well the rocks are exposed and who owns the land. Often, permits are required to enter and collect fossils on land owned by state or federal governments. These fossils are owned by the public. Only certain types of fossils on public land can be collected without a permit. If the land is privately owned, the fossils are the property of the landowner and he or she must give permission.  

Prospecting and Collecting
When a location has been chosen, the next step is to begin prospecting. Prospecting is searching the ground for fossils and deciding whether any important fossils lies underneath. Searching for fossils in most areas is very time consuming and often frustrating when, after many days of searching, nothing of interest turns up. But there is no better feeling of satisfaction than making a new find. When a paleontologist finds a fossil, they must be careful to plot its position on a map so the place can be found again. The fossil or its wrapping is also labeled and notes made so that it can be associated later with its location. 
In some areas fossils are collected from surface finds only. Elsewhere a surface find may indicate that digging could uncover more fossils. If fossils are small and relatively durable, they may be collected simply by putting them into a box or vial with a little padding. Large fossils, such as those of dinosaurs, may require large- scale excavation and sophisticated wrapping and reinforcement to keep the fragile specimens from breaking up. Paleontologists usually try to identify what they have found while still in the field. But dirt and rock covering a fossil may make identification difficult, and too much preparation (cleaning) under field conditions may damage the specimen. Thus, careful preparation and study are usually saved for the laboratory. Because of this, exciting discoveries are often made after specimens have been returned to the museum and prepared.
Collecting fossils usually involves collecting more than the fossils themselves. Fossils are useful only if details about where and how they were collected are also recorded. Field paleontologists take careful notes and record everything they find. They record the kind of rock and the position in the sequence of sedimentary rocks where the fossils were found. Knowing the kind of rock that fossils are preserved in helps put together the story of the environment in which the fossilized plant or animal lived and how it came to be a fossil. When the location of each fossil find and any other information the paleontologist thinks important have been recorded, then it is time to go to the museum.  

Museum Preparation
The first step on returning to the museum is to clean the remaining dirt off the fossil, and glue it together if it is broken so it can be handled and stored. This is called preparation. A preparator is a person trained in the techniques of excavating, cleaning, and strengthening fossils. A preparator also needs to have training in the anatomy of the creatures he or she is preparing, so that important details will not be overlooked or destroyed.  

After the fossil is clean and stabilized it can be studied, displayed, or stored for future use. Preparators quite often paint a permanent number on fossils similar to a library catalog number on a book so they can be found later. A collections manager is the person responsible for storing and keeping track of all the fossils in a museum collection.  There are several ways that a fossil can be useful once it is in a museum. Most fossils are part of research collections. Paleontologists use research collections to study the anatomy of the plants and animals they are interested in. A museum scientist, called a curator, specializes in the types of plants or animals in a collection. Curators often write books or shorter articles about their research interests. They often use the research collections of many museums to do their work. Public exhibits constitute another part of a museum's mission. Displays of fossils allow the museum curator's scientific findings to be made available to a wider audience than if they were only described in print. Displays allow fossils and other natural objects to serve an educational purpose for schools and the general public. This is important because museums depend on the general public, either directly, through museum memberships and contributions, or indirectly, through government grants, for the funding that allows them to do their work. Also, paleontologists are justifiably proud of their finds and are eager to share them with as many people as possible.  

Conservation of Paleontological Resources
Paleontologists have a code of ethics that guides them in their work and encourages the most efficient use of the resource. They are careful to get permission from the owner of the land on which they intend to work. If the land is owned by a state or federal government, they must apply for a permit to work there. Application for a permit requires describing what the paleontologist wants to look for and why, what kind of digging will be required, and how long the project will take. Paleontologists try to disturb the land only as much as necessary to extract the fossils. They also remember to close gates and not disturb livestock that may be present. Most paleontologists agree that vertebrate fossils, because of their rarity, should be collected and used primarily for scientific research and teaching. Generally, vertebrate fossils are not collected simply to be sold. Because of the quality of molding and casting today, high-quality plastic casts can take the place of actual fossils when it is necessary to share fossils with other museums, schools, or private individuals. 

Fossils are Nonrenewable Natural Resources
Fossils of all kinds are the only direct evidence we have of past life. As such they are irreplaceable natural resources for science. It is important for students to understand that fossils should be used wisely, and that they can participate in their conservation. Private collecting of fossils can be a good thing, but amateur paleontologists should always follow standards of professional ethics, including discussing their finds with experts in a position to recognize exceptional or valuable specimens. Good field records are necessary so that all finds can be exactly relocated. In addition, it is important for children to learn to respect public and private lands by not trespassing and by obtaining permission to dig or collect specimens.  

Protection of fossil resources is aided by public facilities such as the National Park System and on lands administered by other federal agencies. In national parks and monuments, fossils are protected from destruction and made available for educational and scientific use by the public. 


After reading the background information, gather the following materials

For How Living Things Become Fossils Lesson Plan 
Paper cups
Liquid mud or clay of two or more contrasting colors
Bones, shells, leaves, or other possible fossils  
Plastic spoons, toothpicks, or small nails

For Making a Trace Fossil Lesson Plan
Shallow trays or pie plates  
Modeling clay  
Carving tools such as plastic knives and spoons, popsicle sticks, etc.  
Specimen cards

For Some Parts Make Better Fossils than Others Lesson Plan
Horse skeleton diagram  
Stegosaurus skeleton diagram  
Drawing/coloring utensils


Step One: Teacher reads background material on A Fossil’s Journey found on this page.

Step Two: Complete How Living Things Become Fossils Lesson Plan.

Step Three: Complete Making a Trace Fossil Lesson Plan.

Step Four: Complete Some Parts Make Better Fossils than Others Lesson Plan.

Step Five: Complete the Post-Unit Questions found on this page.


Clastic Sediments: sediments result from the breakdown, through weathering, of pre-existing rocks.
Curator: a museum scientist. 
Diagenesis: everything that happens to sediment after it is deposited. A potential fossil may be dissolved in the process of diagenesis, and other times it may become mineralized.
Fossil: any naturally occurring evidence of past life. Fossils need not be mineralized or enclosed in rock.
Organic sediments:  pieces of tissues of plants or animals such as leaf litter on a forest floor.
Paleontologists:  scientists who study fossils to understand the history of life on Earth.
Preparation:  when paleontologist clean dirt and surrounding rocks off the fossil, glue it together (if broken) and store it. 
Prospecting:  to search the ground for fossils. 
Metamorphic rocks: rocks changed by heat and pressure.
Mineralization or Petrification:  the condition when a fossil has effectively turned to stone.
Trace Fossil:  an impression of the animal or plant after its death such as a natural mold of a shell.
Sedimentary Structures:  non-biological processes preserved in rocks like ancient ripple marks, mud cracks, or raindrops preserved in rock.  They do not represent activities of living things, and they are not trace fossils.

Assessment Materials

A Fossil’s Journey Post-Unit Questions

Students answer questions after completing all three activities: How Living Things Become Fossils, Making a Trace Fossil, and Some Parts Make Better Fossils than Others activity.

1. In what type of rock are fossils usually found? 

2. Where are some places that fossils are likely to be found? 

3. What are some requirements for fossilization? 

4. Is fossilization common or rare? 

5. Give an example of a trace fossil. 

6. How do paleontologists find fossils? 

7. What happens to a fossil after it has been excavated? 

Rubric/Answer Key

1. In what type of rock are fossils usually found? 
Sedimentary Rock. 
2. Where are some places that fossils are likely to be found? 
Lake bottom, river sandbar, beach, ocean floor, dune field. 
3. What are some requirements for fossilization? 
Hard parts, rapid burial, protective medium, diagenesis. 
4. Is fossilization common or rare? 
5. Give an example of a trace fossil. 
Footprints, burrows, coprolites. 
6. How do paleontologists find fossils? 
Geologic map, prospecting. 
7. What happens to a fossil after it has been excavated? 
It is taken to a lab where a lab preparator cleans it and then a curator displays it in a collection for public learning. 

Additional Resources

Audubon Society Field Guide to Rocks and Minerals
Introductory geology textbook 

Related Lessons or Education Materials

National Park Service Fossil Educational Activities Webpage
Fossil Butte National Monument: Making a Fossil Game

Contact Information

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Last updated: April 15, 2020