Body : [ Background Knowledge: One of the unique features of Earth is its water. In both liquid and frozen forms, water covers approximately two-thirds of the Earth's surface. Geologic evidence suggests that large amounts of water have likely flowed on Earth for the past 3.8 billion years -- most of its existence. Water is necessary for the development and nourishment of life.]
Show students a vase of blue water, a rock, and a ball. The water in the vase represents the water on the Earth's surface, and the rock represents the land on the Earth's surface. The ball gives students a visual image of the shape of the Earth. Ask students, "Where do we find water? Where do we find land?"
Give each student a Prediction Sheet (see Materials ). The handout shows a blank Earth, with the words Land and Water printed at the bottom of the page. Students are instructed to draw in the amount of land and water that they believe is on Earth. Then students decide if the land area they drew is greater, equal, or less than the area of water they drew. Students will indicate this by placing a greater than sign, an equal sign, or a less than sign between the two words.
Next, divide students into three groups of eight, including one recorder and seven globe tossers (these numbers will vary depending on the size of the class). Give each recorder a Data Sheet (see Materials ). The rest of the students in the group will stand in a circle and take turns tossing the globe across the circle to another student. When a student catches the globe, the student will look at the area surrounding his/her right thumb. If the thumb is pointing to land, the student reports, land ; if the thumb is touching water, then water is reported. The recorder writes land or water on the spaces provided on the Data Sheet.
After 35 trials in small groups, the students will come together in a large group to compile their data. Ask the recorders to share their data and list the results on the board. The three numbers generated from the land trials are added together and written on the board, and the same is done for the water trials. Ask students which number is greater -- the data they retrieved for land or the data they retrieved for water. (Students should find that their fingers pointed to areas of water at least two times out of three.) Ask students how the results compare to their earlier predictions.
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