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11.1: Fossils

Difficulty Level: At Grade Created by: CK-12
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Lesson 11.1: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. Preserved traces can include burrows.

_____ 2. Scientists have discovered fossil footprints.

_____ 3. Complete preservation occurs only when remains are preserved in rock.

_____ 4. It is very likely that any given organism will become a fossil.

_____ 5. Fossils of ocean animals have been found at the top of Mt. Everest.

_____ 6. Fossils show that Antarctica once had a much warmer climate.

_____ 7. Index fossils are the first fossils ever discovered of an extinct species.

_____ 8. Teeth are more likely than feathers to be preserved as fossils.

_____ 9. People first started discovering fossils about 150 years ago.

_____ 10. All fossils form when remains of dead organisms are covered with sediments.

Lesson 11.1: Critical Reading

Name___________________ Class______________ Date________

Read this passage based on the text and answer the questions that follow.

How Fossils Form

The process by which remains or traces of once-living things become fossils is called fossilization. Most fossils form when a dead organism is buried by sediments. Layers of sediment slowly build up. Through time, the pressure of additional sediment layers turns the lower layers into sedimentary rock. The remains inside the rock layers also turn to rock. The remains are replaced by minerals, so they literally turn to stone.

There are several other ways in which fossils may form. Tree sap may cover an organism and then turn to amber. The organism encased in the amber is completely preserved. Scientists might even be able to study its DNA. Organisms can also be completely preserved in tar or ice. Molds and casts are other ways organisms can be fossilized. A mold is an imprint of an organism left in rock when the organism's remains break down completely. If rock fills in a mold, it forms a fossil called a cast. The cast resembles the original remains. Molds and casts usually form in sedimentary rock. Yet another way fossils form is by compression. Compression occurs when an organism's remains are put under great pressure inside rock layers. This leaves behind a dark stain in the rock. The stain is the same shape as the original remains.


  1. Define fossilization.
  2. Explain how most fossils form.
  3. Identify and describe three other ways in which fossils may form.

Lesson 11.1: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. Which of the following parts of organisms are most likely to be fossilized?
    1. skin
    2. hair
    3. shells
    4. internal organs
  2. Preserved traces of organisms might include
    1. casts.
    2. feces.
    3. molds.
    4. compressions.
  3. Preserved remains that have become fossils have turned to
    1. tar.
    2. rock.
    3. amber.
    4. none of the above
  4. Which type of organism’s remains are least likely to be preserved as fossils?
    1. jellyfish
    2. salmon
    3. shark
    4. tuna
  5. Fossils can show us
    1. how extinct organisms looked.
    2. what past environments were like.
    3. what geological processes occurred in the past.
    4. all of the above
  6. To be used as index fossils, fossils must represent an organism that
    1. lived in the water.
    2. lived over a wide area.
    3. lived for a long period of time.
    4. lived less than 5 million years ago.

Lesson 11.1: Matching

Name___________________ Class______________ Date________

Match each definition with the correct term.


_____ 1. dark stain in rock left by the remains of an organism

_____ 2. preserved tracks or other evidence of an organism that lived in the past

_____ 3. type of fossil that can be used to determine the age of rock layers

_____ 4. process by which remains or traces of living things become fossils

_____ 5. type of fossil that forms in a mold

_____ 6. any preserved remains or traces of an organism that lived in the past

_____ 7. imprint of an organism left in rock


a. fossil

b. mold

c. index fossil

d. cast

e. trace fossil

f. fossilization

g. compression

Lesson 11.1: Fill in the Blank

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

  1. Most fossils are preserved in __________ rock.
  2. As the remains of an organism change to a fossil, they are replaced by __________.
  3. An organism may be preserved if it is covered by tree sap that turns to __________.
  4. __________ provide the best clues about the history of life on Earth.
  5. A trilobite fossil is an example of a(n) __________ fossil.
  6. Most preserved remains are __________ parts of organisms such as bones.
  7. Most fossils form when a dead organism is buried by __________.

Lesson 11.1: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Explain how index fossils are used and what properties of fossils make them useful for this purpose.

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