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13.2: Lesson 13.1: Water on Earth

Difficulty Level: At Grade Created by: CK-12
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Key Concepts

  • Description of water
  • Distribution of Earth’s water
  • The water cycle

Lesson Objectives

  • Describe water and where it occurs on Earth.
  • Give an overview of the water cycle.

Lesson Vocabulary

  • condensation: process in which a gas changes to a liquid
  • evaporation: process in which a liquid changes to a gas
  • fresh water: water that contains little or no dissolved salts and is found in streams, lakes, ice, the ground, and the atmosphere
  • infiltration: process in which water seeps into the ground
  • precipitation: water that falls from clouds to the ground as rain, snow, sleet, or hail
  • runoff: precipitation that flows over the surface of the land
  • transpiration: release of water vapor into the atmosphere from the leaves of plants
  • water: simple chemical compound, each molecule of which contains two atoms of hydrogen and one atom of oxygen (H2O)
  • water cycle: continuous movement of water through the oceans, atmosphere, ground, and living things

Teaching Strategies

Introducing the Lesson

Students are likely to have prior knowledge of the water cycle from earlier science classes. Help them recall this prior knowledge. Call on students to state what they already know about the water cycle. Ask a volunteer to record their statements on the board. Tell students they will learn more about the water cycle when they read this lesson.


Use the aquarium demonstration at the following URL to show students how Earth’s water is distributed. The demonstration will impress upon them how little fresh water is available for human use. The demonstration procedure is followed by a handout worksheet and discussion questions.


Using Visuals

Have students look at the figure in the FlexBook® lesson that shows the distribution of the world’s water. Make sure they realize that fresh water accounts for only 3 percent of all water on Earth. Discuss how the fresh water is distributed so they understand how to read the diagram.

Question: In what state is most of the fresh water on Earth?
Answer: Most (79%) of the fresh water on Earth is in the solid state as ice in ice caps and glaciers.
Question: Of all the fresh water on Earth, what percent is liquid water on Earth’s surface or water vapor?
Answer: Only 1 percent of all fresh water is liquid surface water or water vapor.
Question: Where is the majority of fresh surface water found?
Answer: The majority (52%) of fresh surface water is found in lakes.
Question: Where is more of Earth’s fresh water located: under the ground or in the atmosphere?
Answer: Much more is located under the ground than in the atmosphere.


Demonstrate the water cycle to the class by playing the water cycle animation at this URL: http://www.epa.gov/safewater/kids/flash/flash_watercycle.html.

Differentiated Instruction

Give students copies of an unlabeled water cycle diagram, such as the diagram at the URL below. Tell students to label the diagram with the correct processes. They can refer to the water cycle diagram in the FlexBook® lesson if they need help with any of the processes.



Ask one or more students to make a crossword puzzle using all of the lesson’s vocabulary terms. They can create their puzzle by hand or use a free online puzzle maker (see URL below). Distribute copies of their puzzle for the rest of the class to solve as a review of lesson vocabulary.


Science Inquiry

Have students model the water cycle in a closed environment. This will give them a better understanding of the processes involved. You can use the activity at this URL:


Common Misconceptions

Students tend to have a number of misconceptions about the water cycle. For example, they may think that the water cycle involves freezing and melting of water. Make sure they understand that the water cycle involves evaporation of liquid water, condensation of water vapor, and precipitation (rain, sleet, hail, or snow). You can find other misconceptions about the water cycle at the following URL. The Web site also explains how the misconceptions develop and how to correct them.


Language Arts Connection

Using the activity at the URL below, students will create the life story of a single drop of water. This will reinforce their understanding of the water cycle and the processes it includes.


Reinforce and Review

Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Earth Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.

Lesson Review Questions

Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.

Lesson Quiz

Check students’ mastery of the lesson with Lesson 13.1 Quiz in CK–12 MS Earth Science Assessments.

Points to Consider

As water moves through the water cycle, it spends some time on Earth’s surface as fresh water. Where is fresh water found on Earth’s surface?

How do people use fresh water on Earth’s surface?

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