Engage (15 minutes):
Divide the class into groups of 4-5 students. Each group needs a piece of chart paper and markers. Give each group five minutes to list all the places water is found on Earth. Tell students to circle the source on their list that they think contains the most water, and have groups discuss what type of water is found in this location and why they think it has the most water.
Have students create a pie chart that shows what they think is on the earth’s surface in terms of land and water. (If students are not familiar with pie charts, explain that the entire circle is the whole pie or 100%. Put a dot in the center of the circle and divide the circle in half. Each half represents 50%. Divide each half into five equal slices. Each slice then represents 10% of the total pie. Have students color the slices that represent land green and the slices that represent the water blue.) Students should label the pie chart and write the percentages of their predictions in a key. Hang charts around the room. Discuss the similarities and differences in groups’ predictions.
Explore (30 minutes):
Show students pictures of Earth (p. 3-5 of NASA Mission Geography handouts) Discuss why Earth is often called “the blue planet.” Identify what the different colors in the pictures represent.
Give each group of students an inflatable globe and a copy of p. 1 of NASA Mission Geography handouts. Have students find the oceans and continents on the globe. Have students roll or toss the inflatable globe 100 times and tally where the student’s pointer finger touches on each catch. (Have students rotate the recording job every 10 tosses so each student in the groups has a turn to record and toss.)
After 100 tosses, have students find the total number of water catches by adding up the ocean tallies. Find the total number of land catches by adding up the continent tallies. Convert these totals into percentages of the entire Earth’s surface. Discuss: Did every group get the same percentages? Why or why not? Were the groups’ results close? What does this tell us about Earth’s surface?
Give each student p.2 of NASA Mission Geography handouts. Have students answer the questions and make a pie chart of their data. Compare it to the groups’ original graphs to determine whether their predictions were accurate. A full description of this activity can be found at http://missiongeography.org/I-2-1.pdf.
Explain (30 minutes):
Explain that even though most of Earth is covered by water, only a small part of it is freshwater. We know saw that most of Earth’s water is in oceans, which is saltwater. Pour 100 ML water into a graduated cylinder. This represents all Earth’s water (100%). Pour 3 ML of that water into a second graduated cylinder. This represents Earth’s freshwater. The remaining 97% (97 ML) is saltwater. (Add a pinch of salt to that water.) Have students discuss the implications of such as small percentage of water available for drinking, farming, washing, and all other human uses. Have students make a bar graph representing this distribution on the handout in the attachments section.
Use Wiki How tutorial to explain how to create a pie chart of the same information or use this procedure: Draw a radius in the circle. Ask students how many degrees are in a full circle (360). Tell them to multiply the percentage (expressed as a decimal) by the number of degrees in a circle (360) using the calculators to see how many degrees of the circle represent fresh and salt water. Model how to measure the number of degrees for each slice of the pie. Have students color in and label sections for freshwater and saltwater.
Watch NASA “Show Me the Water” video.
Use a gallon of colored water to represent all the water in the world. Divide the class into 6 groups with each group representing one source of water: ice, groundwater, lakes, swamps, rivers, and oceans. Divide water among groups based on each source (ice: 20.6 mL, groundwater: 9.0 mL, lakes: 0.08 mL, swamps: 0.01 mL - roughly 5 drops, rivers: 0.002 mL - roughly 1 drop, and the rest stays in the jug to represent oceans). For a full description of this activity, see “A Drop of Water in Your Cup” from the California Academy of Sciences. Have students discuss anything that is surprising about the distribution.
Elaborate (30 minutes):
Read One Well: The Story of Water on Earth. Discuss how the percentage of freshwater on Earth is so small that water is a scarce resource in some areas. Have students create a model of where Earth’s freshwater is using colored water graduated cylinders. Explain that the lakes, swamps, and rivers are all surface water, so pour the liquid from those cups in the previous demonstration into one cup. Explain that the students will use 100 ML of water to show where all this freshwater is on Earth.
Each group needs a 100 mL graduated cylinder, three clear plastic cups, colored water, three index cards, and a graphing sheet (from the Attachments section).
- Measure 12 mL water into a clear plastic cup. This will represent the amount of available surface water. Write “Surface Water” on an index card and place it next to this cup.
- Measure 27 mL water into a second cup and label it “Ground Water.”
- The remaining water (61 mL) represents water in glaciers and ice caps.
Have students graph data (bar graph and pie chart form) and use their graphs as evidence to construct an argument that water should be conserved.
