Many scientists study objects and events that they cannot observe directly. But through extensive sampling, observation, and analysis, scientists are able to construct a plausible series of explanations to describe subjects ranging from the birth of our solar system to the lives of extinct creatures. For example, paleontologists work to unravel the stories of our past through the collection and analysis of fossil evidence. In this lesson, students explore how they can learn about events that have occurred in the past by using the scientific process. They make observations, develop a hypothesis, and use evidence to test their hypothesis to see how well it holds up in light of the evidence they have.
- Make accurate observations of evidence and record data
- Use indirect evidence to make predictions
- Develop a plausible hypothesis to describe events that cannot be observed
- Practice analyzing evidence
- Use the scientific process to solve a mystery
Grade Level: 6-8
Two to three class periods
- Plate Tectonics: The Scientist Behind the Theory QuickTime Video
- Plate Tectonics: Further Evidence QuickTime Video
- What Killed the Dinosaurs? Shockwave Interactive
- When Did the First Americans Arrive? QuickTime Video
- Earthquakes: Los Angeles QuickTime Video
- Science journals for students to record their observations
- Observation Activity Image PDF Image
- Mystery Shopper Worksheet PDF Document
Before the Lesson
- Make copies of the worksheet.
- If possible, arrange computer access for all students to work individually or in pairs.
Part I: Making Observations and Gathering Evidence
1. Begin by explaining to students that the goal of this lesson is to construct a plausible series of hypotheses to describe events that they cannot observe and that they will use the scientific process to test those hypotheses. Then project the Observation Activity Image PDF Image in front of the class, but do not tell students anything about the content of the picture. Divide the class into small groups and ask them to answer the question, What happened here? Students should support their responses with any prior knowledge they have (e.g., "I've seen pictures of earthquake damage that look like this" or "There was an earthquake in my town that caused this kind of damage"). As the students work, circulate among the groups to push for additional details, such as any observations they make that suggest how strong the earthquake may have been. As a rule of thumb, observations made with a purpose are apt to be more productive than those made without.
2. Ask students to share their observations with the class, and make a list of all responses on the board. As students list their observations, help them distinguish between fact (e.g., part of the roof is missing...) and inference (e.g., something big knocked the wall...). Also, point out that a hypothesis is like an inference?
3. When the list is complete, tell students that their observations of the structure are clues to a past event. As scientists, their next step is to develop a hypothesis that explains what may have happened to the structure. Discuss the following:
- What is an observation? What is a hypothesis?
- What hypothesis might you make based on your observations? What might you do next to try to test your hypothesis?
- What branches of science use evidence to uncover the past?
4. One such branch of science is geology. Show the Plate Tectonics: The Scientist Behind the Theory QuickTime Video and the Plate Tectonics: Further Evidence QuickTime Video and discuss the types of evidence that have been collected to support the theory of plate tectonics. Ask students:
- What evidence did Wegener use to support his theory? What evidence was he unable to provide?
- Why did geologists hesitate to believe Wegener's theory?
- What evidence finally showed that plate tectonics was indeed a reliable theory?
Part II: Using Evidence to Support or Challenge a Hypothesis
5. Discuss the scientific process of gathering evidence to support a hypothesis. Then have students explore the What Killed the Dinosaurs? Shockwave Interactive in pairs. Ask them to discuss which hypothesis about dinosaur extinction appears to be the most probable and why.
6. Show the When Did the First Americans Arrive? QuickTime Video. Then discuss the following with the class:
- What older evidence supported the hypothesis that the Native Americans came to the continent over the Bering Strait from Asia 12,000 years ago?
- What newer evidence challenges this hypothesis?
- What is the new, or current, hypothesis?
- What do you think would be the next step for scientists studying the human population in North America?
7. Ask students to consider how evidence of past events can help scientists predict future events. Then show the Earthquakes: Los Angeles QuickTime Video and discuss the following:
- What evidence did scientists discover that shifted their thinking about the earthquake threat to Los Angeles?
- Why are there so many small, fractured thrust faults near Los Angeles? What are the implications for the city?
8. Tell students that they will now attempt to solve a mystery by making observations and developing a hypothesis.
- Have students work in pairs to study the grocery receipts on the Mystery Shopper Worksheet PDF Document. Each pair should make a list of observations about the items they see on each receipt.
- Students should begin to develop a profile of the mystery shopper(s). Ask each pair to write a short description of the shopper(s) based on the information in each receipt.
- When they are ready, have each pair share their hypothesis with the class. Then discuss in a large group which hypothesis is most plausible based on the information in the receipts? The following questions can help get the discussion started:
- Are the receipts from one shopper or two?
- Are the shoppers male or female?
- Do they live with other people or alone?
- What type of food do they eat?
- What time of year is it?
- How old are the shoppers and (if appropriate) the members of their households?
Check for Understanding
- What is important to consider when making observations?
- How does a scientist develop a hypothesis?
- Name some significant hypotheses that scientists have developed?
- How does your experience doing the Mystery Shopper activity (in which you interpreted the evidence without seeing anyone else's interpretation first) compare with your experience doing the video-viewing activities (in which you made sense of other scientists' interpretations of the events)? What is the same? What is different?
The Digital Library for Earth System Education (www.dlese.org) offers access to additional resources on this topic.