Ask the students these questions and record responses in a location that will be visible throughout the lesson:
1. What do you know about water?
2. Why is water important to life on Earth?
Have students stand in a circle and softly toss the inflatable globe to one another. Have each student remember if their thumb landed on land or water. The majority should have landed on water.
Ask the students: Why do you think so many of us landed on water?
Students should express the idea that our Earth is covered mostly by water.
Ask the students: What percentage of the Earth's surface is covered by water?
Allow them to guess or predict what they think.
Tell students that 70-75% of Earth's surface is covered by water.
Teacher: So if 70-75% of Earth is covered by water, then we should have plenty of water, right? Let's find out.
Tell each group that the 5-gallon container represents all of the water on Earth. Have the students use their plastic syringes to remove the following amounts of water from the large container and then place those amounts into the individual cups. Each portion measured should be placed in a separate cup.
Have the groups label their cups by placing a sticky note beside each cup with the following information:
0.2 mL= fresh water as water vapor
0.9 mL= fresh water in soil
1.7 mL= fresh water in rivers, streams, lakes
118 mL (1/2 C)= fresh water in groundwater
414 mL (1 3/4 C)= fresh water in polar caps and glaciers
Ask the students:
What is left in the large container?
What does this represent?
Be sure that students understand that the water remaining in the large container represents salt water and that salt water cannot be consumed by plants and animals on Earth because of its salt content.
Have students calculate the percentage that each amount represents out of all the water on Earth.
The total amount in the bucket was 18,927 mL before any water was removed.
The bucket now contains 18,394.7 mL To find the percentages, students should use the calculator and divide the amount in each cup by the total amount in the bucket.
Freshwater rivers, streams, lakes=0.009%
Polar Ice Caps and Glaciers=2.2%
Oceans and other saltwater sources=97.2%
Now since students have calculated the percentages, have each student record them on one side of an index card. Have students turn and talk to a partner and discuss why they think this is significant/important.
Show the video: Why Care About Water? (National Geographic)
As a formative assessment, students should write these percentages on one side of an index card. On the opposite side, students should explain why this is important for us to understand.