Modelling Earth’s Inner Structure

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The purpose of the following lessons is to build on the reasoning behind the rejection of Wegener’s Continental Drift Theory. Most students are convinced that the continents have moved over time. Now the goal is to try and uncover how that is possible by examining what scientists have learned about Earth’s inner structure–something that Wegener was unable to do. The scientific and engineering practices I have chosen to teach about Earth’s layers are for students to use mathematics to develop a scale model of Earth’s layers and to use it to communicate information and also make predictions about how Earth’s structure affects how it functions (specifically related to earthquakes, volcanoes, the continental drift theory, mountain building..).

There are several reasons why creating a scale model is an effective strategy for teaching about Earth’s inner structure. The 6th and 7th  grade Common Core math curriculum has a heavy focus on Ratios and Proportional Relationships.  Creating scale models in science class is one way to reinforce those math skills. But even more powerful is when students begin to understand just how small we are compared to the Earth and how much there is left to explore. It deepens their sense of awe about the tremendous forces that we will learn about that shape our Earth. Scaling Earth’s layers lets us see the big picture and enables us to make predictions on how the parts work together (structure and function). It also helps to expose misconceptions: especially the notion that we are floating on a layer of magma. I hang up a few scale models in the classroom to refer to for the rest of the unit(for example: identifying where plates are located, or how deep magma chambers are, or how deep the focus of specific earthquakes are located…)

Key Ideas From the Lessons
  • Use mathematics to develop a scale model of Earth’s interior layers. For each layer, use symbols to communicate important facts about that layer. Use the scale model to make predictions about how Earth’s structure affects how it functions specifically related to earthquakes, volcanoes, the continental drift theory, mountain building…
  • Within a natural or designed system the transfer of energy drives the motion and/or cycling of matter.
  • An object will sink if its density is greater than the density of the fluid it is in; it will float if its density is less than the fluid it is in.
  • Rocks can be solid, liquid, or in a slightly softened form.
  • The Earth is divided into 3 main layers: crust, mantle, and core. The top part of the mantle, along with the crust, forms structures know as tectonic or lithospheric plates.
  • The interior of the earth is hot.
  • Seismic waves transfer energy through the layers of the Earth and across its surface
Summary of lessons: 

Lesson 1: Ask students if it is hard to imagine the size of Mt. Everest or T-Rex? What would help clarify?  Begin a discussion about the importance of scale models. The first lesson focuses on exploring how to set up proportional relationships to determine the scale model’s measurements. Students watch this video and then explore the interactive. I ask them to come up with a formula that solves each of the scenarios given. It takes a while but when it starts to click, they get real excited. The formula should some version of A/B=C/D. I do not let the students use cross-multiplication to solve for the unknown variable since it is “illegal” algebra. Instead, we analyze how their proportion was set up to make sure it is telling the story of how the variables are related and then use inverse operations to find the unknown. I like this book to help me make sure that I’m teaching mathematics and not “tricks”. Nix the Tricks: A guide to avoiding shortcuts that cut out math concept development. Then, I challenge the class to “shrink” Mt. Everest so that it would fit in the length of the hallway (2 dimensionally). We will then shrink ourselves the same proportion and draw mini-me (stick figures) to get an idea of  height of the tallest mountain on Earth (at sea level and not at the equator) Mount Everest.  The mini me’s are going to be very small!! We then go in the hallway. One end is the imaginary base of Everest and the other end is the top. I have the students line up their mini me’s at the base and imagine they are now going to climb up Mt. Everest. We come back to the classroom and discuss the power of scaling. How did it change their perspective of Mt. Everest? How does scaling make big numbers such as 8, 848 meters (the height of Everest) more meaningful?

These are the students’ pages I created to help them with the task for lesson 1 and lesson 2. Feel free to download and modify for your needs. Creating scale models

Lesson 2: Introduce the project of creating a scale model of Earth’s interior. Go over instructions. After calculations are done every group (groups of 3) draw the layer lines together. I needed to tape two pieces of 11 X 17 construction paper to be able to fit the model.  Begin by everyone completing the 63 cm and 52 cm lines together (these are horizontal lines). Have students label the boundary line AND the actual layer–inner core. Have students label the surface/sky. Point out that further down in the data table you will be creating holes, mountains, and aircraft- not layers. Once layers are complete students spend one day researching the layers, using their book, notes, and internet and developing symbols to represent the facts. Students have been very clever when choosing symbols such as making solid layers look like bricks.; drawing an ice-cream cone becoming more melted as it gets deeper to show temperature difference; drawing a person become more crushed as they get deeper to represent pressure change. Thinking of symbols “force” students to understand what the facts mean. Make sure they symbolize convection currents in the asthenosphere and outer core and that the only layer that is liquid is the outer core. Also, symbols that show the lithosphere is broken into pieces.

Lesson 3: Students will have many questions after the models. For example: If we humans have only explored a tiny sliver of the crust, how do scientists “know” what’s all the way at the core? I have some videos in resource section below that address that question. They also might not understand how the asthenosphere is solid but can flow. Use silly putty to model the asthenosphere: (Pass out silly putty to each group). Let students explore the silly putty-ask guiding questions–What layer do you think this represents and why? How is it like a solid and how is it like a liquid? What would happen if i poured water on your desk? Would it flow? What about this silly putty? Do you think it would flow? Have students roll the silly putty into a ball and place it on the center of a paper and trace around it. Make predictions. Leave it alone for 30 minutes. Then retrace the silly putty. Observe how it has flowed. Compare that to the asthenosphere. Do you remember how thermal energy in  fluids are transferred? (Convection currents) There are convection currents in this layer because it can flow. Ask students to analyze their scale models and make predictions of how Earth’s structure helps explain earthquakes, volcanoes, the continental drift theory, mountain building.  They WILL NOT have all the answers based on the model–the idea is to get them starting to think about what causes these phenomena.



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