1. Introduce the concept of land use by looking at global land use history.

Show the A Tale of Two Planets image. (Download the image by clicking on the down arrow in the lower right corner of the media carousel window.) These maps illustrate which land areas have been changed by humans over time. Tell students that humans have changed Earth's landscapes greatly over time. Have students study the evidence of change illustrated on the map models. Then ask:

• Which areas have been changed by humans for the longest period? (Europe, Central America, the Middle East, India, and eastern Asia have been used intensively for thousands of years, along with some areas along the Andes Mountains in South America, northeastern North America, and parts of sub-Saharan Africa. The orange to red coloration on the map shows this.)

• How do you think humans changed the land? (Humans have used the land for farming as well as housing.)

2. Discuss the role of uncertainty in the scientific process.

Tell students that science is a process of learning how the world works and that scientists do not know the “right” answers when they start to investigate a question. Students can see examples of scientists' uncertainty in forecasting crop yields. Show the Projection of Maize Crop Yields in France image from the media carousel above. (Download the image by clicking on the down arrow in the lower right corner of the carousel window.) Tell students that the graphs in this image show the projection of maize crop yields in France over this time period—the average daily precipitation, number of hot days, and yield of maize. The gray line shows the predictions for crop yield based on technological improvements. The pink shading shows the expected yield based on temperature and precipitation influences. The red lines outside the pink shading show the total uncertainty. Ask:

• Does the technology trend (gray line) accurately predict crop yields? (No, the technology trend does not accurately predict crop yields. This is because crop yields are dependent on temperature and precipitation as well as technological improvements.)

• Why do you think the crop models still have uncertainty even after accounting for precipitation and temperature differences year to year? (Student answers will vary. The crop yield could be affected by a pest infestation.)

Tell students they will be asked questions about the certainty of their predictions and that they should think about what scientific data is available as they assess their certainty with their answers. Encourage students to discuss the scientific evidence with each other to better assess their level of certainty with their predictions.

3. Introduce the concept of stocks and flows in a system.

Tell students that materials flow into and out of systems. The flow of the materials over time can change and can be influenced by many different factors and interacting parts.

Scientists think about how one part of the system can affect other parts of the system. Give students a simple example of a stock and flow in a system, as described in the scenario below.

There is a bathtub with water flowing in from the faucet and water leaving through the drain. Ask:

• When the drain is plugged, what happens to the level of water in the bathtub? (The water level will increase because the outflow of water is stopped, but water keeps coming in from the faucet.)

• When the faucet is turned off, what happens to the level of water in the bathtub? (The water level will decrease because the inflow of water is stopped, but the water keeps leaving through the drain.)

• How can the level of water in the bathtub be kept at the same level? (The water in the bathtub can be kept at the same level by making the inflow equal to the outflow. Then the water that comes in through the faucet will be offset by the water that leaves through the drain.)

4. Implement the Using the Land interactive.

Provide students with the link to the Using the Land interactive. Divide students into groups of two or three, with two being the ideal grouping to allow groups to share a computer workstation. Tell students they will be working through a series of pages of questions related to the data in the interactive. Ask students to work through the interactive in their groups, discussing and responding to questions as they go.

NOTE: You can access the Answer Key for students' questions—and save students' data for online grading—through a free registration on the High-Adventure Science portal page.

Tell students that this is Activity 2 of the Can We Feed the Growing Population? lesson.

5. Discuss the issues.

After students have completed the activity, bring the groups back together and lead a discussion focusing on these questions:

• How have humans changed Earth's natural landscape? (Humans have cut down forests and plowed up prairies for farming and housing. Waterways have been changed for irrigation and to prevent seasonal flooding. Other areas have been less affected by human actions, but there are few places on Earth that have not been affected by human actions.)

• What is a consequence of turning forested land into farmland or residential land? (The forests provide homes for many organisms. Many forest lands are sloped, which may not be good for either farming or housing. Forests provide oxygen, prevent water runoff and erosion, and store carbon dioxide.)

• How has the proportion of agricultural land in the United States changed since 1950? (Agricultural land has decreased. Urban areas have increased, as have special use areas [parks, wilderness areas, defense/industrial lands]).

• Why isn't agricultural land spread evenly around the world? (Agricultural land needs to have good soil, adequate precipitation, and moderate temperature. These features aren't found evenly across Earth.)