Unit 3.6 Why do plates "tectonic"?

By the end of this unit, students will be able to:

• Use density of materials to explain lithosphere-mantle structure
• Use mechanical behavior of materials to explain lithosphere-mantle relationship
• Design a physical model that represents the structure of Earth's lithosphere and mantle to use for experiments that model convergent plate boundary interactions
• Apply density and mechanical behavior of Earth materials to explain why different types of convergent plate boundaries exist

Following the density of solid materials and layered structure of the Earth, this module is designed to facilitate students experimentally investigating how and why different convergent plate boundary types exist based on the density and mechanical behavior of Earth materials. The lab activity is intended to provide real-world context for the students to apply their density measurements and their scaled drawing of Earth's layers. Students will use the knowledge gained from prior modules to design a model for observing how density contrasts drive convergent plate boundary interactions.

These materials build a foundation for understanding the unit's motivating question, but also function well as a standalone module or they can be used as extension materials for classes with labs (while omitted from curriculum for classes without labs). The materials in this unit should take 140 min of class time. This lab relies on small group work and experimentation with tubs of liquid, so it is best suited to a lab meet-up outside of a traditional lecture room.

In this course, plate tectonics is implicitly or explicitly a theme in three of the main overarching units: Unit 2.5 about the Hunga Tonga Volcano's energy, this unit on density and layering (Units 3.5 & 3.6), and Unit 4.3 on Forces. Complete all of these parts so that your students can build a deep understanding by viewing this topic through different lenses.

Teaching Materials:

All Slides: Unit 3.6 All Slides (PowerPoint 2007 (.pptx) 4.8MB Aug28 24)

Tectonic Drivers Video: A_002_TectonicDrivers.mp4 (MP4 Video 28.2MB Jul11 24)

Demonstration spring to show 3 regimes of elastic, plastic deformation, and fracture. Note: be prepared to damage this spring by showing plastic deformation. A homemade spring can be made by wrapping a metal clothes hanger around a paper towel tube.

Modeling Convergent Boundaries Activity materials needed for each group:

• Transparent tubs
• Fluid(s) to represent the mantle (preferably viscous and transparent, like glycerine, gelatin, water thickened with cornstarch to make gravy, or agar-agar. In piloting, water worked well as well)
  • Recipe to make cornstarch "gravy": boil 2.5 gallons of water, turn off the heat, slowly stir in a 16oz box of cornstarch with a whisk until fully thickened. Note: left sitting at room temperature for days, this will mold.)
• Solids to represent the crust (ex: Cork sheets, Foam sheets (various thicknesses), styrofoam sheets, sponges, plexible plastic sheets/cutting boards)

Reflection Assignment: Unit3.6_reflection.docx (Microsoft Word 2007 (.docx) 68kB Jul11 24)

Sample Student Reflections (this is Reflection 11): Reflection Examples Redacted.pdf (Acrobat (PDF) 1.8MB Jul8 24)

The Lab(s) is/are assessed as a Science Journal, as always. Science Journal TIDeS Instructions (Microsoft Word 2007 (.docx) 2.9MB Aug30 24)

Scientist Spotlight Full Resource (In this unit: Marie Tharp): Scientist Spotlight Slides (PowerPoint 2007 (.pptx) 4.6MB Jul8 24)

Other Materials: computer and projector, white board or chalk board with markers/chalk.

Pre-Class Assignment(s):

Pre-class reading: Scientist Spotlight Marie Tharp

• Spend a few minutes online doing additional research on Marie Tharp and be prepared to share something surprising or interesting that you learned about her.

Watch this 7-minute video: What are the forces that drive plate tectonics? A_002_TectonicDrivers.mp4 (MP4 Video 28.2MB Jul11 24) Discuss at least three interesting observations or questions you have from watching the video.

In Class, Class Discussion and Lab Activity: Modeling Convergent Boundaries (140 min)

Whole-Class Introduction (30 min): Intro to geologic structures, plate boundaries, and landforms

• Begin by showing IRIS video (what are the forces that drive plate tectonics?) to remind students about plate motions and ask for their observations from before class.
• Think-pair-share to recall previous unit content (the plan for this module is to integrate the previous unit content with the application of plate motions).
  • Consider the uppermost 250 km of the Earth
  • Describe the differences and relationships between the materials that comprise Earth's "thin outer skin"
• Introduce the concept of geologic structures: faults and folds result from the movement of tectonic plates and the mechanical properties of the crust.
• Showing photos of folded and faulted rock (and folded ice), think-pair-share:
  • Explain how you think these different structures result based on your understanding of Earth materials and their mechanical behavior
• Explain brittle and ductile deformation resulting from different stresses and resulting in different geologic structures, then connect these different stresses to the different plate motions and types of boundaries
• Showing the basic three plate boundaries, think-pair-share:
  • What landforms do you expect to find at the different types of plate boundaries and why?
  • Explain how you think these different landforms result based on your understanding of Earth materials mechanical behavior and density
• Leads into activity: Modeling plate tectonics through a "lens of density"

Lab exercise Modeling Convergent Boundaries (90 min)

• In small groups, students will design models based on density contrasts to show how plates "tectonic".
• Students will choose materials to represent the asthenosphere and the lithospheric plates and design experiments to model convergent boundary interactions (subduction and collision).
• Students must sketch their plan first, identifying what materials they intend to use and why, then build and test their design to explore what is working and what isn't working.
• Groups will then collaborate with neighboring groups to show their work and discuss their issues. Groups will peer-review each other, then set off to make revisions to materials, design, or both.
• Upon revision and testing, groups now consider if and how their revision impacted their model.
• Following revision, all groups share out to the class with demonstrations and discussion of what they felt worked best in their model.
• Think-pair-share:
  • Given what you know about density of Earth materials & Earth's layers, can you hypothesize why subduction and collision happens?
  • Can you hypothesize why magma upwelling occurs at divergent boundaries?
• Final lab reflection questions are:
  • What materials (and why) did you choose to represent which Earth layers?
  • Were you able to represent the functions due to density that you hoped for with your model?
  • How did you use the revision and class sharing process to modify your model and your understanding of plate tectonic processes?

Whole-class Wrap Up (20 min): Plate boundaries, volcanoes, and density

• Showing a map of plate boundaries and volcano locations to start class, ask if they notice any pattern
• Open questions: what is the liquid form of rock? How do you make a rock liquid? (remind them to think in terms of density)
  • Rock (solid) is more dense. Lava/magma (liquid) is less dense. How do we convert a solid to a liquid? 1) Heat to melt it. 2) Pressure... LESS pressure – depressurize it – to move the atoms farther apart from each other. Examples for pressure: dry ice (sold) vs CO₂ gas. High pressure to make CO₂ into solid. Liquid nitrogen vs N₂ gas, again, requires high pressure to convert gas to liquid. The same thing works for volcanism at divergent boundaries: decompression melting.
• Now show volcano examples, one from a subduction zone and one from a rift zone to represent this concept in the real world.
• Final wrap up discussion for the unit: What questions do you have about plate tectonic processes that remain unanswered after this examination through the "lens of density"?

This unit includes one of many Scientist Spotlights. The goal of these is to showcase an array of scientists in fields relevant to the topics of the day, some from long ago and others young and active today, together representing a diversity of people who have all overcome some challenge in pursuit of their scientific passion.

A pre-class assignment (described above) is graded for completion only, not correctness. Administer using the same format throughout your course (through the LMS, turn in paper copies, guided discussion/participation in class, etc.). Consider setting the due date an hour or so before your class begins to give you time to summarize where your students sit with these concepts (this is a form of Just in Time Teaching).

The Lab is assessed as a Science Journal, as always. Science/Lab Journals General Instructions/Rubric (Microsoft Word 2007 (.docx) 2.9MB Aug30 24)

The reflection assignment in this unit asks students to reflect on a reading assignment plate boundaries and forces. Reflections ask students to put their learning in their own words and also to apply their knowledge in a new and novel situation. As always, reflections should be about 500 words and they should both discuss content that reflects understanding and thoughtfully reflect on the materials.

• Read Plate boundaries and forces and reflect on the following questions:
  • What information and/or concepts do you understand that help you explain how plate tectonics works?
  • What information and/or concepts are missing from your learning so far to complete your understanding of plate tectonics?
  • Explain using specific examples that showcase your understanding!

Video introducing plate motions is from IRIS here. The video can be downloaded and embedded or played online.

End unit reading from Vision Learning

• Plate boundaries and forces

There are a handful of references and resources that are relevant to plate tectonics and specific to the Hunga Tonga volcanic eruption in the References and Resources section of Unit 2.5: System Mapping.