Academic standards correlations on Teachers' Domain use the Achievement Standards Network (ASN) database of state and national standards, provided to NSDL projects courtesy of JES & Co.
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Water is a crucial ingredient for life on Earth: It nourishes people, plants, and animals and plays a major role in the planet's weather and climate. The water cycle is Earth's natural mechanism for transporting, cleansing, and recycling water between the surface and the atmosphere. In this lesson, students recognize the different forms that water takes and learn about where it exists in the environment. Through class discussion and experiments, students model the water cycle and explore how it can be used to create fresh water.
Two to three class periods
Familiarize yourself with the videos so that you will know when to pause them. Organize the materials into kits for each pair/team. Prepare a small dish of salt solution a few days in advance so that it has time to evaporate and leave behind salt crystals.
1. Begin by asking the class, "What is water?" Record their responses on the board. Then ask:
2. Show the Water Phases Flash Image. Discuss the three phases of water. Allow students to handle some liquid water and ice. Explain that water vapor is invisible but present in the air. Then ask:
3. Discuss where each form of water is found on Earth. Ask:
4. Show the Global Water Distribution Flash Interactive. Discuss the main difference between water in lakes and rivers (fresh water) and water in the ocean (salt water).
5. Discuss what precipitation is and the different kinds of precipitation. Show the Observe Precipitation QuickTime Video. Ask:
6. Discuss how water is continuously cycled between Earth's surface and the atmosphere. Show the Water Cycle Animation QuickTime Video once in its entirety. Play the animation again, pausing at each transition to have students explain what is happening to the water in each stage.
(Optional) For older students, discuss the steps of the water cycle in more detail by going through The Hydrologic Cycle Flash Interactive together.
7. Show the first segment of the Biome in a Baggie QuickTime Video. (Stop before the host starts assembling the biome.) Ask students what they think she is making. After the class has discussed the project, continue to play the video to show the assembly instructions. Stop before the explanation about how the biome works.
8. Have students work in pairs to create their own biome in a baggie. Distribute the supplies and lead the class through the steps. After the biomes are assembled, discuss how the water will move and if this is similar to the way water behaves on Earth. Ask:
9. Show the rest of the Biome in a Baggie QuickTime Video and compare your class discussion with the explanation given.
10. Optional) Have students make observations of their biomes over the next few days. Ask:
11. Review the major steps in the water cycle: evaporation, condensation, and precipitation. Have students discuss the importance of the water cycle in maintaining fresh water on Earth. Ask:
12. Explain that the class is going to conduct a second experiment related to the water cycle. Remind students that water exists on Earth in both salt and fresh water forms, but that the fresh water supply is very limited. The task here is to find a way to make salt water into drinkable fresh water. Break the class into teams to brainstorm solutions. Show, but do not distribute, the supplies that are available to them.
13. Discuss the ideas that the groups come up with. Show the first two minutes of the [Solar Still Part I: Salt Water video], stopping before the explanation of how the still works. Distribute the supplies and have the teams assemble their own solar stills. Note: Remind students to keep the cups clean to avoid contaminating the experiment.
14. Discuss how the solar stills will purify the salty water. Students should recognize that when water evaporates from a solution, the solute stays behind. As an example, show them your prepared dish of salt crystals left behind after a salt solution has had time to evaporate. Show the end of the Solar Still Part I: Salt Water QuickTime Video, and compare your class discussion with the explanation given.
15. Place the stills in a sunny location and check on them in a few hours. If you are comfortable with it, allow students to taste their distilled water. Discuss how the distillation process of the solar stills is related to the water cycle. Note: There probably won't be much water distilled in just a few hours -- let the stills work for a few days to produce more fresh water.
Have students discuss the following:
The Digital Library for Earth System Education (www.dlese.org) offers access to additional resources on this topic.