Unveiling Earth's Layers: Discovering the Mohorovičić Discontinuity

Earth & Space Science Grades High School 6:13 Video
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Lesson Description

Explore the groundbreaking discovery of the Mohorovičić Discontinuity (Moho) and how it revealed the layered structure of our planet through seismic wave analysis.

Video Resource

The mohorovicic seismic discontinuity | Cosmology & Astronomy | Khan Academy

Khan Academy

Duration: 6:13
Watch on YouTube

Key Concepts

  • Seismic waves and their behavior
  • Refraction of seismic waves at boundaries
  • The Mohorovičić Discontinuity (Moho) as the boundary between the crust and the mantle
  • Earth's layered structure
  • Using seismic data to infer Earth's internal composition

Learning Objectives

  • Explain how the analysis of seismic waves led to the discovery of the Moho.
  • Describe the difference in density between the Earth's crust and mantle.
  • Define the Mohorovičić Discontinuity and its significance.
  • Illustrate how seismic wave refraction provides evidence for Earth's layered structure.
  • Apply the concept of seismic wave velocity to infer the composition of Earth's interior.

Educator Instructions

  • Introduction (5 mins)
    Begin by discussing the structure of Earth and what students already know. Ask if anyone knows how we know about the layers within Earth, since we can't directly observe them. Briefly introduce Andrija Mohorovičić and the puzzle he solved.
  • Video Viewing (7 mins)
    Play the Khan Academy video: 'The mohorovicic seismic discontinuity | Cosmology & Astronomy | Khan Academy'. Instruct students to take notes on key terms, the experiment, and the conclusions.
  • Discussion (8 mins)
    Lead a class discussion based on the discussion questions. Encourage students to share their thoughts and interpretations of the video. Focus on understanding the relationship between seismic wave velocity and density.
  • Interactive Exercise: Modeling Seismic Wave Refraction (10 mins)
    Complete the interactive exercise. Have the students work in pairs.
  • Wrap-up & Assessment (5 mins)
    Summarize the main points of the lesson. Administer the multiple-choice and fill-in-the-blank quizzes to assess student understanding.

Interactive Exercises

  • Seismic Wave Simulation
    Use a simulation (if available, otherwise, a drawing exercise) to model the refraction of seismic waves at the crust-mantle boundary. Students can adjust the density of the layers and observe the changes in wave behavior. Have them draw the path of P and S waves.

Discussion Questions

  • How did Andrija Mohorovičić use seismic waves to determine that the Earth has layers?
  • Why do seismic waves travel faster in the mantle than in the crust?
  • What does the Mohorovičić Discontinuity represent?
  • How does the study of earthquakes help us understand the Earth's internal structure?
  • Why is the discovery of the Moho so important?

Skills Developed

  • Scientific Inquiry
  • Data Interpretation
  • Critical Thinking
  • Model Building
  • Problem-Solving

Multiple Choice Questions

Question 1:

The Mohorovičić Discontinuity marks the boundary between which two layers of the Earth?

Correct Answer: Crust and Mantle

Question 2:

Who discovered the Mohorovičić Discontinuity?

Correct Answer: Andrija Mohorovičić

Question 3:

What evidence did Mohorovičić use to identify the discontinuity?

Correct Answer: Changes in seismic wave velocity

Question 4:

Seismic waves travel faster in the mantle compared to the crust because the mantle is:

Correct Answer: More dense

Question 5:

The bending of seismic waves as they pass from one layer to another is called:

Correct Answer: Refraction

Question 6:

Why were seismographic stations important to Mohorovičić's discovery?

Correct Answer: They recorded the arrival times of seismic waves

Question 7:

Approximately how far away from the earthquake did Mohorovičić observe the change in seismic wave velocity?

Correct Answer: 200 kilometers

Question 8:

What type of wave does the video describe in relation to discovering the Moho?

Correct Answer: Body waves

Question 9:

Which of these statements is true about Earth's crust?

Correct Answer: It is the thinnest layer

Question 10:

Why is the mantle denser than the crust?

Correct Answer: Because it is made up of heavier elements

Fill in the Blank Questions

Question 1:

The boundary between the Earth's crust and mantle is called the _______________ Discontinuity.

Correct Answer: Mohorovičić

Question 2:

Seismic waves change _______ as they pass from one layer to another because of density differences.

Correct Answer: velocity

Question 3:

The Moho was discovered by analyzing data from a(n) _______________ in Croatia.

Correct Answer: earthquake

Question 4:

The bending of seismic waves as they pass through different materials is called _______________.

Correct Answer: refraction

Question 5:

The layer of Earth that is directly below the crust is the _______________.

Correct Answer: mantle

Question 6:

Seismic waves that travel through the Earth's interior are called _______________ waves.

Correct Answer: body

Question 7:

The Earth's _______________ is composed of both oceanic and continental types.

Correct Answer: crust

Question 8:

Mohorovičić noticed that at distances greater than 200 km, seismic waves arrived _______________ than expected.

Correct Answer: faster

Question 9:

The difference in seismic wave speed led Mohorovičić to conclude that the mantle is _______________ than the crust.

Correct Answer: denser

Question 10:

The Mohorovičić discontinuity is also known as the _______________ for short.

Correct Answer: Moho

Educational Standards

ES.ESS2.1:[Standard] Develop a model to illustrate how Earth’s internal and surface processes operate at different scales of space and time to form continental and ocean-floor features. ES.ESS1.6:[Standard] Apply scientific reasoning and evidence from ancient Earth materials, meteorites, and other planetary surfaces to construct an account of changes in Earth’s formation and early history. ES.ESS2.3:[Standard] Develop a model based on evidence of Earth’s interior to describe the cycling of matter by thermal convection.

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