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Lesson Plan: Evidence for Evolution

Overview

In this lesson, students learn about the fossil record, the primary type of evidence scientists use to piece together the history of life and to support and refine the theory of evolution. The lesson begins with an overview of the fossil formation process, then covers the evolution of land-dwelling animals from fish, and finally looks at how some mammals (whales) ended up back in the water.

Objectives

Suggested Time

Resources

Materials

Before the Lesson

The Lesson

Part I: Fossil Formation

1. Have students watch the Becoming a Fossil video. Then discuss the following:

  • Why do most living things not leave fossils behind?
  • How are fossils formed?
  • How are fossils uncovered?
  • How do scientists determine the age of fossils?

2. Have students watch the Laetoli Footprints video. Then discuss the following:

  • What was the unusual series of circumstances that caused the Laetoli footprints to be preserved? Does this combination of events say anything about why such footprints are a rare find?
  • What do the footprints at Laetoli tell scientists about the way the creatures that made them moved?

3. Have students watch the Radiometric Dating video. Then discuss the process of radiometric dating, as well as other methods of dating fossil finds.

Part II: Evidence of the Evolutionary Process

4. Have students watch the Fish with Fingers video. Then discuss the following:

  • What did old theories say about the evolution of land-dwelling animals, and why was paleontologist Jenny Clack dissatisfied with these explanations?
  • What evidence did Clack find to disprove old theories?
  • What explanation of the evolution of land animals can Clack give based on current fossil evidence?

5. Have students examine the Tetrapod Limbs image. Then discuss the image with students, focusing on these specific questions:

  • What are the similarities and differences among the seven limbs shown?
  • How would scientists explain why these very different species all have limbs with five digits?
  • What is the difference between a homologous structure and an analogous structure? Name some examples of each.

6. Show the Evolving Ideas: How Do We Know Evolution Happens? video and discuss the following:

  • What can we learn from fossil evidence?
  • What specific fossil evidence points to the whale's evolution from land to water?

Part III: Whale Evolution

7. Pass out copies of the Whales in the Making handout and the Whale Evolution Data Table Worksheet (PDF) worksheet. Have students work in teams of two. Ask them to cut out the six fossil boxes from the handout and gather information about each fossil from resources in the Evolution Library (http://www.pbs.org/wgbh/evolution/library) or in books from the school library.

8. Ask each team of two to prepare an Eocene epoch timeline on paper, using the same scale as the classroom model (one inch equals one million years). Their timelines should be twenty-one inches long. Each million years should be labeled, with 34 Mya at the top of the timeline and 55 Mya at the bottom.

9. Have teams mount fossil boxes 1 and 2 from the handout at the proper locations on their timelines. Point out the large gap between these two fossils. Then have students add the remaining fossils in order by the age of the fossil (from youngest to oldest).

10. Discuss the following:

  • What typical whalelike traits were apparently the earliest to appear? What apparently evolved much later?
  • As each "missing link" was found, how many new gaps were formed? What is the relationship between gaps and fossils?
  • To find fossil evidence to fill the largest remaining gap in whale evolution, what age sediments would you search?
  • What distinguishing traits would you expect to find in whale fossils of that age?

Check for Understanding

To help students synthesize what they've learned about evolution from these activities, ask them to discuss the following: