Grade: Grade 6 Subject: Science Unit: Plate Tectonics Lesson: 3 of 6 ACT: Science

Investigation Lab: Plate Boundaries

Learn

In this investigation lab, you will model the three types of plate boundaries and observe how tectonic forces shape Earth's surface. Scientists use models to understand processes that occur over millions of years or deep within Earth where direct observation is impossible.

Types of Plate Boundaries

Earth's lithosphere is divided into approximately 15 major tectonic plates that interact at their edges. These interactions create three distinct boundary types:

  • Divergent boundaries: Plates move apart from each other. Magma rises to fill the gap, creating new oceanic crust. Example: Mid-Atlantic Ridge.
  • Convergent boundaries: Plates move toward each other. One plate may subduct (dive beneath) the other, or both may crumple upward. Example: Himalayan Mountains, Cascadia Subduction Zone.
  • Transform boundaries: Plates slide horizontally past each other. No crust is created or destroyed, but earthquakes are common. Example: San Andreas Fault.

Investigation Question

How do different plate boundary interactions affect Earth's surface features?

Materials Needed

  • Graham crackers (2 per station)
  • Frosting or cool whip (represents asthenosphere)
  • Wax paper or plastic plate
  • Small cup of water
  • Paper towels
  • Lab notebook

Safety Considerations

  • Do not eat lab materials unless instructed by your teacher
  • Clean up all materials after the investigation
  • Wash hands before and after the lab

Examples

Modeling Divergent Boundaries

Procedure:

  1. Spread a thin layer of frosting on your plate (this represents the asthenosphere).
  2. Place two graham cracker halves side by side on the frosting.
  3. Slowly push down and pull the crackers apart.

Expected observation: The frosting rises up between the crackers, modeling how magma rises at mid-ocean ridges to form new seafloor.

Modeling Convergent Boundaries (Ocean-Ocean)

Procedure:

  1. Dip one edge of a graham cracker in water for 10 seconds (this makes it denser, like older oceanic crust).
  2. Place both crackers on fresh frosting.
  3. Slowly push them together.

Expected observation: The wet (denser) cracker slides beneath the dry one, modeling subduction. The frosting may bulge up, representing volcanic activity.

Modeling Transform Boundaries

Procedure:

  1. Place two crackers side by side touching each other.
  2. Press down gently while sliding one cracker forward and the other backward.

Expected observation: The crackers catch and release, sometimes breaking at the edges. This models how faults build up stress and release it suddenly as earthquakes.

Practice

Complete these practice questions based on the investigation concepts.

1. In the divergent boundary model, what does the frosting rising between the graham crackers represent?

Think about what happens at mid-ocean ridges.

2. Why did we make one graham cracker wet before modeling the convergent boundary?

Consider how density affects subduction.

3. What real-world feature would form at a divergent plate boundary in the ocean?

New crust is being created here.

4. Explain why transform boundaries cause earthquakes but do not create mountains or volcanoes.

Think about the direction of plate movement.

5. A scientist observes a deep ocean trench next to a chain of volcanic islands. What type of plate boundary is likely present? Explain your reasoning.

6. Compare and contrast what happens to Earth's crust at divergent versus convergent boundaries.

7. The Himalayan Mountains formed when the Indian plate collided with the Eurasian plate. Both plates contain continental crust. Why do mountains form instead of subduction in this case?

Consider the density of continental versus oceanic crust.

8. Identify one limitation of using graham crackers and frosting to model plate tectonics. How does this limitation affect what we can learn from the model?

9. Based on the investigation, predict what surface features you would expect to find along the boundary between the Pacific Plate and the North American Plate near California.

10. Design a simple test you could add to this investigation to model what happens when two continental plates converge. What materials would you use and why?

Check Your Understanding

Reflect on these questions to assess your learning from this investigation.

  1. Can you identify all three types of plate boundaries and describe the motion at each?
  2. Can you explain why different boundary types create different geological features?
  3. Can you connect your model observations to real-world examples?
  4. Can you identify strengths and limitations of the graham cracker model?

Next Steps

  • Complete your lab report with detailed observations and analysis
  • Research a specific plate boundary and create a diagram showing its features
  • Continue to the next lesson on analyzing plate tectonics data and graphs