Directions

4. Have children apply their understanding of habitability factors by using the craft materials to construct or draw a cross-section of a planet that can support life at the surface.

• Distribute the "What Makes a World Habitable" sheet.
• Review the sheet to show how it can help children develop their habitable planet.
• Have children reform the teams they were in when playing the board game.
• Define cross-section. Give them 10–15 minutes to create their cross-sectional view.

Because Earth is a natural model for children to use, most will depict an Earth-like planet. This outcome is fine because it puts the habitability factors in a familiar context and reinforces the idea that they are inter-related. Earth is the only planet we know of with life, and much of it is at the surface. Point out how the “What Makes a World Habitable” sheet summarizes the information on the game cards and game board. The sheet will help them include all the factors at levels just right for supporting life.

5. Reconvene the group. To process Step 4, call out a habitability factor and have children point to where this factor is found on their models/drawings. Do this with all five factors. After reviewing all five factors, ask teams to share any special features of their worlds.

Avoid over-processing these models/drawings. These same themes will be discussed again in Part C when children create a planet with habitable conditions beneath the surface.

6. Discuss the following questions:

• Which of the five habitability factors are found far beneath the surface?
• What might be some of the characteristics of organisms that live beneath the surface?

Children may mention life, such as worms, insects, fish, and burrowing animals. Although such creatures have underground homes, they are still considered surface life because their lives depend entirely on surface processes (rain, food, warmth). Conversely, subterranean life gets its energy, nutrients, and water from subterranean sources. Bacteria have been found deep in the crust, around volcanic vents on the ocean floor, and in caves.May 11, 2005o miles below the surface. The crucial point is that when we talk about life beneath a planet's surface, we are talking about microbial life. Subterranean life is single-celled, microbial life, not, as Hollywood might have you believe, an advanced civilization of humanoid creatures living vast subterranean cities!