The next three lessons help students understand how scientists find evidence of evolution and piece together the history of life. In this lesson, students learn about the fossil record, the primary form of evidence. 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.
- Learn how scientists use fossil evidence to trace the evolution of various species
- Understand methods used to date fossils
- Two to three class periods
- Becoming a Fossil Video
- Radiometric Dating Video
- Record of Time PDF Document
- Mike Novacek: Fossils in the Gobi HTML Document
- Fish with Fingers QuickTime Video
- Ted Daeschler and Neil Shubin: Early Tetrapod Fossils HTML Document
- Evolving Ideas: How Do We Know Evolution Happens? Video
- Whales in the Making PDF Document
- Whale Evolution Data Table Worksheet PDF Document
Use these resources to create a simple assessment or video-based assignment with the Lesson Builder tool on PBS LearningMedia.
Before the Lesson
- Make copies of Whales in the Making handout and theWhale Evolution Data Table Worksheet (PDF) worksheet
After the Lesson
Discuss these general questions about fossil evidence:
- What are some key examples of fossil evidence that support the theory of evolution?
- Why are fossils so rare, and why is it difficult to find an evolutionary trail of fossil species leading from a common ancestor?
- What questions remain unanswered by relying solely on the fossil record?
Part I: Fossil Formation
1. Have your class watch the Becoming a Fossil video and read the backgrounder. Discuss the following questions with your class:
- Why do most living things not leave fossils behind?
- How are fossils formed?
- How are fossils found?
- How do scientists determine the age of fossils?
2. Have your students watch the Radiometric Dating video and take notes. Then discuss in class the process of radiometric dating.
3. Have students visit Record of Time Web site for more information on dating methods. Then divide the class into four groups and assign each group one of the following topics: fossil formation, relative dating methods, radiometric dating, and other chronometric techniques. Have each group collect information on their assigned topic from either Record of Time Web site or another source and make a worksheet for their classmates. The next day, ask the groups to exchange worksheets and complete them for homework. On the third day, discuss the results in class.
4. Have the class read the interview Mike Novacek: Fossils in the Gobi. This interview will give them a good sense of what it's like to be a paleontologist. It shows how an individual scientist contributes to the fossil record and our understanding of evolution. Discuss the following questions with your class:
- Who is Roy Chapman Andrews? (You may want to bring in some books about him, in case your students want to know more about this Indiana Jones-type character.)
- Why were Andrews's mammal fossil finds important?
- What did Novacek learn about mammals from the dinosaur age? What evidence did he find to draw these conclusions?
- What did Novacek learn about the transitions in mammalian evolution?
Part II: Fish with Fingers
5. Have students watch the Fish with Fingers video and read the backgrounder. Discuss the following questions in class:
- Why was Jenny Clack unsatisfied with the explanation of how land-dwelling animals evolved?
- What evidence did she find to disprove old theories?
- What explanation can Clack give based on her fossil evidence?
6. Ask students to read the interview with Ted Daeschler and Neil Shubin called Ted Daeschler and Neil Shubin: Early Tetrapod Fossils. Then have them draw a line down the center of a sheet of paper. In the left column have them list examples of types of fossil structures the scientists found. In the right column have them explain what the scientists learned from this evidence.
Part III: Whale Evolution
7. Show the Evolving Ideas: How Do We Know Evolution Happens? video. Ask students what types of evidence are used to learn about evolution (fossil, molecular, chemical, anatomical), and write the list on the board. Discuss what each term means. Then discuss the following questions with your class:
- What can we learn from fossil evidence?
- How do the transitional fossils of whales support the theory of evolution by natural selection?
- What specific fossil evidence points to whales' evolution from land to water?
8. Prepare a vertical classroom timeline of the Cenozoic era on paper. Make the timeline sixty-five inches tall, and label the topthe present and the bottom 65 million years ago (Mya). Label every million years, with one inch equal to one million years (My). Highlight the Eocene epoch (55-34 Mya). Display the timeline.
9. 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 the data about each fossil from resources in the Evolution Library, the school library, and the Web.
10. 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, with each million years labeled.
11. 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 date of discovery.
12. 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?
- Explain why the absence of transitional fossils does not mean that evolution didn't take place.