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6-8 > Earth Science
Grade level: 6-8 Subject: Earth Science Duration: Two class periods
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Students will understand the following:
1. All the oceans on Earth are really one “world ocean.”
2. Warmer water from the oceans around the equator rises to the top, while colder water from the oceans around the poles sinks to the bottom.
3. Ocean currents are caused by the rising and sinking of warmer and colder water.
4. Ocean currents affect weather and life all over the globe.

For the whole class, you will need a globe, research materials, a computer with Internet access, and access to a freezer. Each group will need the following materials:
Pitcher or container
Tap water
Food dye (dark color)
Ice cube tray
Glass baking dish

1. Divide your class into groups, and have each group prepare for the activity by mixing food dye into water, pouring the water into an ice cube tray, and freezing it.
2. Display a globe and have your students observe that all the oceans on Earth are connected to form one “world ocean.” Ask them where they think the water would be warmer—near the equator or near the poles. Then tell students that they are going to perform an experiment to demonstrate how the colder waters nearer the poles and the warmer waters nearer the equator mix together and move to create ocean currents.
3. The students in each group should fill a clear baking dish with warm tap water to represent the warm water near the equator.
4. Instruct students to place one ice cube at each end of the baking dish, representing the cold water near the poles. Invite them to predict what will happen as the ice cubes melt.
5. Students will observe that the cold (colored) water sinks and moves along the bottom of the baking dish toward the warmer water in the middle; the warmer water moves toward the ends of the baking dish; as the cold water begins to warm, it begins to rise.
6. Students should record the results of their experiment, accompanying their reports with labeled diagrams and an explanation of how differences in water temperature in different parts of the “world ocean” cause ocean currents.
7. Have students use research materials and the Internet to find out more about ocean currents and how they affect our weather and life on Earth.
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Adaptations for Older Students:
Suggest students readKon-Tikiby Thor Heyerdahl to find out how the author replicated the voyage that ancient mariners may have made from Peru to Indonesia on primitive balsa rafts, guided only by ocean currents on which they floated.
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Discussion Questions

1. Explain why the oceans affect Earth’s weather. Consider the weather at the equator in comparison to the weather at the poles. How do the oceans affect the weather in your immediate community?
2. How do oceans deal with the large amount of carbon dioxide produced by humans? What are some ideas that scientists have about the ways global warming will affect the oceans? Should shoreline communities be taking any actions regarding global warming?
3. Discuss why it is important to study ocean currents. Include in your discussion ways that plants, animals, and humans use ocean currents. Are there historical events that were shaped by ocean currents? Are there present-day events that have been impacted by ocean currents?
4. All the water on land eventually reaches the ocean. Discuss how the area you live in impacts the environmental quality of the ocean. Can you describe areas that might add toxic material to the ocean? Are there ways in which your community works to protect the ocean?
5. Debate whether more money should be spent to explore space or to explore the ocean floor.
6. The United Nations has established the Law of the Sea. Discuss how this policy supports the idea that the ocean remains sustainable for the society, culture, and environment of a particular area.
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You can evaluate your students on their reports and diagrams using the following three-point rubric:
  • Three points:reports clear, accurate, and complete; diagrams carefully drawn and labeled

  • Two points:reports accurate and complete, but lacking in clarity; diagrams adequate

  • One point:reports inaccurate, unclear, and incomplete; diagrams carelessly executed

    You can ask your students to contribute to the assessment rubric by determining what information should be included in the reports and which labels should be included in the diagrams.
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“Current Events”
Throughout human history, ocean currents have been crucial in such diverse realms as planetary exploration, garbage dispersal, and the spreading of ocean seeds. From ancient Polynesians floating on a raft between Peru and Indonesia, to ocean-spilled oil soiling remote shorelines, currents have been responsible for taking adventurers, toxins, and sea beans all over the planet. Have your students research either a historical or recent event that in some way involves ocean currents. Each student should prepare a brief report for the class explaining the significance of the event and detailing how ocean currents were involved. Each student may also create an accompanying poster. Conclude by charting each student’s findings on a classwide world ocean map, complete with labels indicating ocean currents.

Ocean Activists
Have students investigate environmental issues concerning the ocean. Examples might include overfishing of Atlantic swordfish; the protection of sea turtles; killer whales attacking sea otters; oil spills; dolphin-safe tuna nets; legal limits to lobster fishing off the coast of Maine; the 200-mile fishing limit; and ocean drilling on the Georges Bank. Let students choose their issues and research the Web and recent articles to gather information that examines these issues from differing perspectives. Once they have collected their information, ask them to write letters to an editor of a journal or to one of their political representatives to express their views on the issues they researched. Make sure their letters include hard scientific figures where applicable. In addition, students could work in groups to design public relations campaigns to increase their community’s awareness of the importance of the ocean. The campaigns could include video spots, posters, advertisements, and leaflets.

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Suggested Readings

An Introduction to the World's Oceans
Alison B. Duxbury. McGraw-Hill, 1996
What affects the flow of the tides? What are ocean currents? How do waves form? This compelling text - designed for students without a background in mathematics, chemistry, physics, geology, or biology - offers answers to these and other basic ocean questions. It emphasizes the role of scientific principles in those processes that govern the seas.

Seas and Oceans
Felicity Brooks, Peter Dennis, and Chris Lyon. EDC Publications, 1994.
This interesting book presents the basic principles of physical geography and the latest scientific research in an exciting and accessible way. Large, detailed diagrams, realistic illustrations, photographs, and maps combine with clear, concise text to make this book a fascinating introduction.

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Ocean Planet Smithsonian Exhibition
This site provides a topic outline, tours of the exhibits and excellent educational materials of the Smithsonian’s exhibit on the world’s oceans and their environmental problems.

Sea World
Although a commercial page, Sea World has an excellent database on marine animals with good links and teacher activities.

The Jason Project
The Jason Project was founded by Dr. Robert Ballard and has teacher materials to support the ongoing Jason Expeditions, which includes marine research.

NOAA Ocean Photo Collection
An excellent collection of marine and ocean photographs maintained by National Oceanic and Atmosphere Administration.

Secrets of the Ocean Realm
Developed by PBS Online, the site has a good collection of lesson plans and a data base of marine animals for student research.

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Click on any of the vocabulary words below to hear them pronounced and used in a sentence.

speaker    bioluminescence
Definition:The emission of light from living organisms as the result of internal chemical changes.
Context:Organisms in deep ocean water produce light and explosions of light by bioluminescence.

speaker    Coriolis effect
Definition:The result of a force in mechanics that deflects the motion of a body as it moves in a rotating system, influencing prevailing winds and ocean currents and named after French physicist Gaspard de Coriolis.
Context:The Coriolis effect causes moving air to bend along the surface as it flows.

speaker    echolocation
Definition:The process of using the speed at which signals travel to determine distance.
Context:Scientists found the Challenger Deep by using echolocation.

speaker    tide
Definition:The alternate rising and falling of the surface of the ocean that occurs twice a day.
Context:The ebb and flow of water due to the tug of the moon and the sun on Earth’s water creates tides.

speaker    wave
Definition:A ridge or swell on the surface of a liquid that normally moves in a forward motion.
Context:A wave is a pattern of flowing water molecules; the water does not move forward with the wave.

speaker    wind
Definition:A natural movement of air.
Context:The movement of air as hot air rises and cold air flows in to take its place is how winds are created on Earth’s surface.

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This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of theMid-continent Research for Education and Learningin Aurora, Colorado.
Grade level:6-8, 9-12
Subject area:science
Understands basic features of Earth.
Benchmark 6-8:
Knows factors that can impact Earth’s climate (e.g., changes in the composition of the atmosphere; changes in ocean temperature; geological shifts, such as meteor impacts, the advance or retreat of glaciers, or a series of volcanic eruptions).

Benchmark 9-12:
Knows how winds and ocean currents are produced on Earth’s surface (e.g., effects of unequal heating of Earth’s land masses, oceans, and air by the sun; effects of gravitational forces acting on layers of different temperatures and densities in the oceans and air; effects of the rotation of Earth).

Grade level:6-8
Subject area:science
Understands energy types, sources, and conversions, and their relationship to heat and temperature.
Knows that heat can be transferred through conduction, convection, and radiation; heat flows from warmer objects to cooler ones until both objects reach the same temperature.

Grade level:6-8, 9-12
Subject area:geography
Knows the physical processes that shape patterns on Earth’s surface.
Benchmark 6-8:
Knows the major processes that shape patterns in the physical environment (e.g., the erosional agents, such as water and ice; earthquake zones and volcanic activity; the ocean circulation system).

Benchmark 6-8:
Understands the effects of different physical cycles (e.g., world atmospheric circulation, ocean circulation) on the physical environment of Earth.

Benchmark 9-12:
Understands the effects of different physical cycles (e.g., world atmospheric circulation, ocean circulation) on the physical environment of Earth.

Grade level:9-12
Subject area:science
Understands how species depend on one another and on the environment for survival.
Knows ways in which humans can modify ecosystems and cause irreversible effects (e.g., human population growth, technology, and consumption; human destruction of habitats through direct harvesting, pollution, and atmospheric changes).

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Mary C. Cahill, middle school science coordinator, Potomac School, McLean, Virginia.
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