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6.4: Lesson 6.3: Seafloor Spreading

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

  • Seafloor bathymetry and seafloor features
  • Seafloor magnetism
  • Seafloor spreading hypothesis

Lesson Objectives

  • List the main features of the seafloor: mid-ocean ridges, deep-sea trenches, and abyssal plains.
  • Describe what seafloor magnetism tells scientists about the seafloor.
  • Describe the process of seafloor spreading.

Lesson Vocabulary

  • echo sounder: device that uses sound waves to calculate distances to underwater objects and the seafloor
  • seafloor spreading: hypothesis explaining how the ocean floor forms and how continents can drift
  • trench: deep crack in the ocean floor

Teaching Strategies

Introducing the Lesson

Introduce seafloor spreading by showing students the animation at the following URL. Challenge students to describe what they are observing. (Magma is erupting onto the ocean floor, and the ocean floor is moving away from both sides of the eruption.) Tell students they will learn more about seafloor spreading and how scientists learned about it when they read this lesson.



You may want to use the excellent PowerPoint presentation at the URL below when you teach this lesson. It provides a concise, logical overview of lesson content.



Use the simple demonstration “Seafloor Spreading Made Easy,” which is described at the URL below, to show students how seafloor spreading occurs. Student volunteers will be actively involved in the classroom demonstration, which could be done as a student activity instead. The demonstration takes about 30 minutes.


Differentiated Instruction

Do a think-pair-share activity for seafloor spreading. Ask students to think about the following questions:

  1. What is seafloor spreading?
  2. What evidence is there for seafloor spreading?
  3. How is seafloor spreading related to continental drift?

After students have had time to consider the questions, divide the class into pairs, and ask partners to share their ideas about the answers to the questions. Be sure to pair any less proficient readers and English language learners with other students in the class.


Ask a student who needs enrichment to make a diagram representing seafloor spreading and the magnetic stripes on the seafloor. Then ask the student to use the diagram to explain the magnetic evidence for seafloor spreading to the rest of the class. A sample diagram can be found at this URL: http://ase.tufts.edu/cosmos/print_images.asp?id=4.

Science Inquiry

With the inquiry activity at the URL below, students will make a paper model illustrating the concept of sea-floor spreading and the development of symmetrical magnetic stripes on either side of a mid-ocean ridge. The Web site provides teacher information as well as a student procedure.


History Connection

Share with students the importance of the American geologist Harry Hess in our understanding of seafloor spreading and its contribution to the theory of plate tectonics. You can find details at this URL: http://pubs.usgs.gov/gip/dynamic/HHH.html.

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 6.3 Quiz in CK-12 Earth Science for Middle School Quizzes and Tests.

Points to Consider

How were the technologies that were developed during World War II used by scientists for the development of the seafloor-spreading hypothesis?

In what two ways did magnetic data lead scientists to understand more about plate tectonics?

How does seafloor spreading provide a mechanism for continental drift?

Describe the features of the North Pacific Ocean basin described in terms of seafloor spreading.

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