Lesson 2 What Happens When Soil Gets Wet?

STUDENT SKILLS: observing, analyzing, classifying, inferring, communicating, comparing,

Lesson 2: What Happens When Soil Gets Wet?

Activity 2A:

What Happens to Water in Soil? SUMMARY: Students will make sedimentators to observe that water behaves differently in various samples. Teacher will demonstrate what happens to water in different types of soil.

KIT MATERIALS: For each group of four students: Plastic cups Bag of premixed soil sample Samples of sand, clay, and humus Plastic spoon Eyedroppers Small paper cups Popsicle sticks Hand lens

TEACHER TO PROVIDE: Copies of MySci™ Journal pages Water Plastic container Paper towels

ENGAGE Ask the children what happens to soil when it rains. How does mud look and feel? Does it feel different from wet sand at the beach or in a sandbox? When you make something out of clay, how does it feel? Divide the class into groups of four. Give each group three paper cups. Fill one with sand, one with clay, and one with humus. Place a small amount of water in each cup. Have the students observe closely and describe how each soil mixture feels. Have the students share their observations with the group, then with the class.

NOTE TO TEACHER: You may want to build a larger sedimentator for the class. Include various rock sizes and sand types.

EXPLORE In their groups, have students create a sedimentator using a plastic cup. Have them predict what they think will happen when water is added to the mixture and it is stirred up. Have them put the premixed soil sample in first, then add water to within one inch of the top. Stir vigorously and set aside undisturbed for at least two minutes. Allow students to make frequent observations. Next, have students examine “sedimentators” that have been sitting undisturbed long enough to have clear water. Encourage them to describe the different particle size (big, medium, and

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Lesson 2: What Happens When Soil Gets Wet?

small) and their arrangement and the clear water.

EXPLAIN Ask the students what they think is happening in their sedimentators. A sedimentator is a device that shows what happens when the components of soil separate out by weight. However it also represents what happens to eroded materials that are transported by water in streams and rivers. Some particles are so small that they are held in suspension permanently; they only settle when the water disappears. Other particles are bigger and are carried along by the velocity of the water. They bounce and somersault along until the velocity diminishes enough for them to settle permanently. The heavier particles are dropped first and then the others are deposited until the finest, lightest ones are finally dropped.

ELABORATE Have the students use their plastic spoons to scoop off the floating materials on the top of their cups. The students will place the material on a paper towel and, using their hand lenses, observe it. Allow students to share their findings with the group.

EVALUATE Have students draw what they noticed with their sedimentators in their MySci™ Journal and give a reason for what they think happened.

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Lesson 2: What Happens When Soil Gets Wet?

Activity 2B:

How Can Water Make a Cave? SUMMARY: Students will observe how water can dissolve some kinds of rock.

KIT MATERIALS: For each group of four students: Modeling clay Sugar cubes (about 30) Toothpicks Clear plastic cups Food coloring (mix with water) Eye droppers Cave diagram Cave video Cave formation pictures Cave brochures Caves and Caverns by Gail Gibbons

TEACHER TO PROVIDE: Copies of MySci™ Journal pages Water

ENGAGE Ask students what they know about caves. What words do they think of? Have any of them ever been in a cave? What was it like? Could they describe it for their classmates? Where are caves found? Does anything live in caves? How are caves formed? How do people use them?

EXPLORE Divide the students into groups of four. Give each group a golf ball-size ball of clay, some sugar cubes (around 30), a clear plastic cup, a toothpick, and some water colored with the food coloring. They should pack the sugar cubes tightly into the cup, about three cubes high (see illustration).

Clay (“ground”) Sugar Cubes (“rocks”)

One student in each group should work the clay until it softens and then should flatten it out. Put the slab of clay in the cup so that it covers the sugar cubes and touches the sides of the cup all the way around.

NOTE TO TEACHER: Drop water in increments of ten drops at a time. Adding too much water will allow the sugar to dissolve without seeing any results.

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Lesson 2: What Happens When Soil Gets Wet?

With the toothpick, poke big holes in the clay. The holes should go all the way through to the sugar cubes. Using the eyedropper, drop the colored water on top of the clay near the holes so that it can drip through them onto the sugar cubes. When the cubes are pretty well colored, tell students to stop adding water and observe their cup. It should take about five to ten minutes to see results.

EXPLAIN Ask the students what they observe happening in their cups. The water will dissolve the sugar in much the same way that groundwater dissolves the bedrock below ground. Explain to the students that the clay represents the surface of the earth and the sugar cubes are the rocks beneath the surface. Explain how the water moves downward and when other substances mix with it, it can make rocks dissolve just like the sugar dissolves. Show the cave diagram and point out the path of the water. The columns, stalactites, and stalagmites grow over the centuries as lime is dissolved out of the ground by rainwater, then slowly deposited again by the water as it drips into a cave. Remember stalactites grow from the ceiling of the cave, and stalagmites grow up from the ground. When they meet, a column is formed. Cave formation is a two-step process that takes place over millions of years. The first step is the process of rain making its way through the layers of leaves, humus, and soil, changing the rain into a weak acid. This solution slowly dissolves the limestone, making holes under the earth. The second part occurs after air pockets are formed in the holes under the earth. As the weak acid drips through the earth and the ceiling of the hole, it leaves a tiny bit of minerals. Drop after drop, fantastic formations begin to form. It may be helpful to draw this process on the board. Read Caves and Caverns by Gail Gibbons and discuss.

ELABORATE Have students watch the cave video and discuss. Students should also look at the cave brochures and cave formation pictures.

EVALUATE Encourage students to write/draw a story in their MySci™ Journal about how rain makes a cave.

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Lesson 2: What Happens When Soil Gets Wet?

NOTE TO TEACHER: Students may make rock candy. The children can record their observations of the rock candy formations in their MySci™ Journal daily. Make the connection to real speleothems. (Refer to background information if needed.) Features such as stalactites and stalagmites are technically called speleothems. Speleothems, sometimes referred to as formations or decorations, are cave features formed by the deposition of minerals. It takes 100 years to make one inch of a stalactite! Have the class together create a graph comparing the growth of their rock candy “stalactites” in one week with a stalactite found in a cave (one inch= 100 years). How old would their “stalactite” be? Rock Candy Ingredients: 1 ½ cups water 6 cups sugar 3 6-inch lengths of string 3 pencils Food coloring Flavoring Directions: 1. Bring water to a boil in saucepan. 2. Remove from heat and add 3 cups of sugar, stirring until dissolved. Slowly add the remaining sugar, reheating the water if necessary. 3. When all the sugar is dissolved, pour the mixture into 3 heat-proof jars or glasses. 4. Stir 3 drops of liquid food coloring and ½ teaspoon of flavoring into each jar. 5. Tie each length of string around the middle of a pencil. Lay the pencils on top of the jars with the string hanging into the liquid. 6. Crystals will begin to form in one hour, and continue to solidify for several days. If a layer forms on the surface of the jar, break it. 7. When the liquid completely evaporates, the candy is ready.

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MySci™ Journal Writing and Drawing Page Name

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