According to the theory of plate tectonics, Earth's crust is composed of a number of individual plates that change shape and position over time. Geophysical evidence indicates that the face of Earth's surface has changed significantly since its initial formation and that the plates on which the continents are located are in constant motion. The movement of the plates is responsible for the formation of ocean basins, mountain ranges, islands, volcanoes, and earthquakes. Important concepts in the theory of plate tectonics include the following:
- The ocean floors are continually moving — spreading from the center, sinking at the edges, and being regenerated.
- Convection currents beneath the plates are responsible for plate movement.
- The source of energy responsible for generating the heat and convection currents that move the plates is most likely radioactivity deep in Earth's mantle.
In this lesson, students are introduced to the theory of plate tectonics and explore how the theory was developed and supported by evidence. Through class discussion, videos, and activities, students seek connections between tectonic activity and geologic features and investigate how the theory of plate tectonics evolved.
- Understand how Earth is dynamic and how moving plates form ocean basins, mountain ranges, islands, volcanoes, and earthquakes
- Identify the three general categories of plate boundaries recognized by scientists: convergent, divergent, and transform
- Understand how the theory of plate tectonics was developed and supported
Grade Level: 6-8
Two class periods
Use these resources to create a simple assessment or video-based assignment with the Lesson Builder tool on PBS LearningMedia.
Before the Lesson
If possible, arrange computer access for all students to work in pairs. Make copies of the World Map With Shorelines and Continental Shelf Boundaries PDF Image to distribute to students. Just before class, have the first two media resources ready: Tectonic Plates, Earthquakes, and Volcanoes Flash Interactive and Plate Tectonics: An Introduction QuickTime Video.
Part I: Introduction to the Theory of Plate Tectonics
1. Discuss how Earth is physically changing and ask students for their ideas about why it changes. Write the term plate tectonics on the board and ask if anyone has heard of this theory. Record class comments on the board and save for later.
2. Show students the locations of earthquakes around the world using the Tectonic Plates, Earthquakes, and Volcanoes Flash Interactive. Switch to the display of volcanoes. Do not show the plate boundaries at this point. Then ask:
- What do you notice about the distribution of earthquakes?
- What do you notice about the distribution of volcanoes?
- Do you see any correlations or patterns?
- Can you think of a possible explanation for the patterns you see?
3. Show the Plate Tectonics: An Introduction QuickTime Video. After viewing the video, return to the Tectonic Plates, Earthquakes, and Volcanoes Flash Interactive and now show the overlay of all three views: earthquakes, volcanoes, and plate boundaries. Point out the Ring of Fire. Ask students to interpret why the active areas are located where they are and to relate their interpretations to their previous comments and possible explanations.
4. Allow time for students to further explore the subject individually or in pairs. Distribute copies of the World Map With Shorelines and Continental Shelf Boundaries PDF Image and have students cut out the continents (following the continental shelf lines) to see how they fit together. At the same time, have students work with the Mountain Maker, Earth Shaker Flash Interactive to learn about the different types of boundaries. During this activity, have students write a list of relevant vocabulary words in their science journal. Encourage students to write the definitions in their own words, but to use the textbooks/computer to verify them.
5. Show the Plate Tectonics: The Scientist Behind the Theory QuickTime Video. Ask:
- Why was Wegener's original idea about continental drift referred to as intuition and not science?
- What did Wegener find that he believed was evidence to support his theory?
- Why didn't others think that his findings constituted evidence?
Part II: Evidence for Plate Tectonics
6. Remind students about the scientific process and discuss the importance of evidence for a scientific theory. Show the Plate Tectonics: Further Evidence QuickTime Video and the Plate Tectonics: Lake Mead, Nevada QuickTime Video. Ask:
- How did the new information about the ocean floor support Wegener's theory?
- How do the rocks at Lake Mead support the theory of plate tectonics?
- What other evidence would help convince you that the theory of plate tectonics was real?
7. The discovery that the ocean floor has a massive ridge running down the middle, that the oldest rocks are farthest from the ridge, and that the banded rock has preserved a record of periodic magnetic reversals are key pieces of evidence for plate tectonics. Have students work in groups to devise a demonstration of how the Atlantic Ocean was formed by sea-floor spreading. You may want to help students get started by discussing ways to represent the spreading apart of the ocean floor and the resulting appearance of the new sea floor. After the students have shown their demos, you may wish to show this effective demonstration:
- Align two desks with their edges just touching — the gap is your mid-ocean ridge.
- Place two pieces of paper vertically into the gap between the desks. Leave just enough of the papers sticking out so that there is something to hold onto.
- Slowly pull the papers out from the gap, spreading the papers apart onto the desks as you go. Make sure that both papers are pulled at the same rate.
- Have a student use a marker to draw a stripe of color on both pieces of paper at the ridge. This stripe of color represents the new rock that is formed at the ridge. As you continue to pull the papers, have the student draw more stripes in alternating colors to represent subsequent time periods. Just make sure each new stripe extends on both sides of the ridge (on both pieces of paper).
- The result should be a mirror-image set of colored stripes, representing how the new ocean floor spreads from the ridge. The discovery of symmetrical rock formations on the Atlantic floor provided strong evidence for the sea-floor spreading theory - the identical patterns showed younger rock near the ridge and contained a record of Earth's changing magnetic polarity through time.
8. Check students' understanding of plate motions by showing the Tectonic Plates and Plate Boundaries Flash Interactive with the color-coded and defined boundaries. Have students indicate which direction the plates are moving at the different types of boundaries. What geologic features could be seen at each boundary?
9. Have students watch the Plate Tectonics: The Hawaiian Archipelago QuickTime Video. Discuss the following:
- What is a hot spot?
- What does it mean to say that a volcano is dormant?
10. Have students work in small groups to simulate the formation of the Hawaiʻian Islands. Distribute the following materials to each group:
- An aluminum pan with about an inch of cornstarch covering the bottom.
- A candle or some other heat source
Have students add small amounts of water to the pan until the cornstarch reaches a pasty consistency. Instruct students to hold one edge of the pan over the candle until bubbles form in the cornstarch. Then tell them to very slowly move the pan across the flame. As the pan moves, they should notice the row of bubbles that is created. Discuss the following:
- What does the candle represent?
- What does the pan represent?
- What does the cornstarch represent?
- What do the bubbles represent?
- The bubbles are similar to a volcano that forms over a hot spot. How do volcanoes form islands?
- Which islands are the oldest?
- Why aren't all of Hawaiʻi's volcanoes active?
11. Revisit the information about plate tectonics that you recorded on the board in Step 1, and update it as needed.
Check for Understanding
Have students discuss the following:
- Why do we call Earth an "active" planet? What does this mean?
- How does the theory of plate tectonics account for earthquakes? Volcanoes? Mountains?
- Hawaiʻi's hot spot doesn't display the typical relationship between volcanoes and plate boundaries, yet it does provide evidence of plate tectonics. How?
- Why was Wegener's theory of continental drift not accepted when he first proposed it? What evidence revealed to scientists that continents could be moving apart from each other?
The Digital Library for Earth System Education (www.dlese.org) offers access to additional resources on this topic.
Grade 6 Earth Science
With input from:
Developed in Conjunction with K-12 Alliance/WestEd
All 6th Grade Earth Science Plate Tectonics Lessons and Literature can be Downloaded hereDownload Complete Grade 6 Earth Science Plate Tectonics
Download Earth Science: Plate Tectonics and Conceptual Flow Narrative PDF
Earth Science: Plate Tectonics
Introduction and Conceptual Flow Narrative
Introduction: This Grade 6 Earth Science Plate Tectonics Unit focuses on plate tectonics and addresses the California Science Standards for 6th grade for the topic of plate tectonics and Investigation and Experimentation. By the end of the unit students will know: Plate tectonics accounts for important features of the Earth’s surface and major geological events. Evidence for plate tectonics is derived from the fit of continents; the location of earthquakes, and midocean ridges; and distribution of fossils, rock types, and ancient climatic zones. The Earth is composed of several layers: a cold, brittle lithosphere, a hot, convecting mantle; and a dense, metallic core. These layers have different densities, compositions and temperatures (energy). Lithospheric plates the size of continents and oceans move at rates of centimeters per year responding to convection currents in the mantle. Geologic events, such as earthquakes and mountain building, result from movement of the plates. Earthquakes are sudden motions along the breaks in the crust called faults and that volcanoes and fissures are locations where magma reaches the surface. Epicenters of earthquake can be determined. The effects of the earthquake on any region varies, depends on the size of the earthquake, the distance of the region from the epicenter, the local geology, and the type of construction in the region. Every plate boundary is a dynamic place resulting in changes to the earth’s surface. Mountains and sea floor trenches can be explained if you understand the possible combinations of crust movement at the boundaries. When two continental plates collide, large mountain ranges (like the Himilaya) are formed. Because an oceanic plate will subduct, deep sea trenches result. Even transform boundaries involve great pressure that can alter land formations and result in small mountain ranges. Major features of California geology, including the Channel Islands, are the result of plate tectonics.
The Grade 6 Earth Science Unit on Plate Tectonics is presented to students through a series of investigations using indirect evidence (models) and direct evidence, experiments, active learning experiences, researching using a variety of sources, questions, and assessments. Assessments include: pre-, post- and 4 formative assessments.
Conceptual Flow Narrative: The Grade 6 Conceptual Flow Narrative for Earth Science: Plate Tectonics builds on the concepts presented on the conceptual flow graphic by describing the concept(s) addressed in each lesson and the links that connect each lesson to the next. Lessons are linked to the previous lesson and the lesson that follows via a conceptual storyline to enable the development of student understanding as they progress from one concept to the next.
After students have completed the Pre-Assessment, they begin their exploration of plate tectonics with Lesson 1, “Densities’ Effect on Layers” which includes three linked sessions building the concept that density determines the order of layering of earth materials. During the first session, students study pictures of the Grand Canyon to raise the question of why Earth materials are in layers on canyon walls. Students observe a model with sediments sinking, floating, or suspending in a liquid. The second session deepens the exploration of how different materials sink or float using the model of diet and regular coke. The third session focuses on relative density through a student exploration of building models with different densities. Students apply concepts of density to explain the layers of Earth materials visible in the Grand Canyon pictures.
In the previous lesson students learned that density of materials determines order of layers. Lesson 2, “Layers of the Earth” includes six sessions establishing how indirect (models) and direct lines of evidence are used to understand that different layers have different densities, compositions, and temperatures (energy). The first session begins with a video exploration showing different layers of the Earth. During session two, students explore how two different models of the Earth represent layers (M&M) and scale (playground). Session three develops an understanding of how indirect evidence is used to build accurate models of the interior of the Earth. Session four demonstrates using a cupcake model of core samples how direct evidence builds knowledge of the top of the crust. Session five uses cooperative groups to research text information about layers of the Earth. The densest layer, the core, is at the center. It is solid on the inside and liquid on the outside. This layer is so dense it produces intense heat. The next middle layer, the mantle, also has two parts like the core. Its outer layer the asthenosphere (mantle) can flow like a liquid. The least dense layer, the lithosphere, floats on the asthenosphere (mantle). The lithosphere is not all one piece. It is composed of large sections called plates that are continually moving. The top of the lithosphere is the crust where we live. In session six, students summarize their learning about Earth layers in a “layer book”.
Formative Assessment #1 is aligned to the concepts in Lessons 1 & 2. As a formative assessment, student answers provide feedback to the teacher and student for any adjustments in the learning. In Formative Assessment #1 students demonstrate their understanding that direct evidence and indirect evidence from models are used to explain how density of materials affects the layering of the Earth. Students are asked to explain how “models of layering” relate to the actual earth layers
Lesson 3, “Convection Currents in the Mantle,” links the exploration of Earth layers from lesson 2 to what causes movement in the layers. Students use convection models to explore how fluids or semi-fluids such as the mantle transfer heat. The model is used to show how the hotter, less dense mantle rises towards the surface where it cools, becomes more dense and sinks back toward the center of the Earth. These convection currents in the mantle constantly and slowly move the plates around.
Formative Assessment #2 is adding the explanation that convection causes movement of the upper level of the mantle and the lower level of the crust. This continuous movement within the mantle causes changes in the crust.
In Lesson 4, “Continental Drift,” students link lesson 3 concept of convection current to changes in the Earth’s crust from one super-continent to present day forms. Evidence on different continents including similar land forms, fossils from similar geologic periods and climatic features such as evidence from glaciers pointed to the super continent Pangaea, followed by millions of years of “Drifting Continents”. Students explore with a newspaper puzzle model explaining how scientists piece together evidence showing continental movement. Wegener’s multiple lines of evidence for continental drift is explored through a “readers theater” bringing a voice to the developing theory. The culminating exploration develops a prediction of where plates will be in 50 million years based on the plate movement from the past 200 million years.
Having learned that continents have moved and are continuing to move in Lesson 4, students in Lesson 5 “Seismic News” explore evidence that years of earthquake records started to give shape to plate boundaries. Students use Internet data to plot current earthquake activity discovering patterns of seismic activity at plate boundaries. Discussions of current earthquakes leads to understanding varying factors that cause damage to structures.
Lesson 6 “Sea Floor Spread” deepens understanding that the evidence from the sea floor- including drilling samples, molten materials and the age of the rock itself, provided the final piece of the puzzle explaining the guiding theory of earth sciences: Plate Tectonics. Students build sea floor models showing ages of the rock combined with a written assignment explaining sea floor spread to parents.
Formative Assessment #3: “Continental Drift and Sea Floor Spread” assesses concepts in lessons 4,5, and 6 that link Wegener’s evidence for continental drift with added evidence of sea floor spread to the growing support for Plate Tectonic theory. Sea floor evidence provided the final data needed to explain plate movement.
While lesson 6 established the final piece of evidence (sea floor spread) for continental drift, Lesson 7, “ Plate Tectonics” includes explorations of different types of movement depending on the density of materials at plate boundaries. Types of boundaries include transform, transverse, and convergent boundaries and result in different landforms. Students map plates and demonstrate understanding of different types of boundaries.
Identifying different types of movements at plate boundaries in the previous lesson are linked to measuring plate movement in Lesson 8 “Dynamic Planet”. Students become experts at the speed and velocity of one piece of 18 individual pieces of the planet (crust). All students in the class collaborate using a process to assemble 18 pieces of the crust into a whole. Arrows and velocities are used to indicate speed and direction of movement.
Having experienced the world view of plate movement in lesson 8, students are able to bring plate movement connections to how local land was formed in Lesson 9, “Channel Island Tectonics” Students use a combination of video explanations and evidence from types of rocks and magnetic direction to construct a model of the Channel Islands’ movement.
Understanding the formation of the Channel Islands in lesson 9 leads to explorations of mountain formation in Lesson 10, “Mountain Building”. When two continental plates converge or collide (convergent boundary), large mountain ranges form (Himalaya). Transform boundaries do not collide but involve great pressure that can alter land formations and result in small mountain ranges. Divergent plates on land result in rift valleys and in the ocean become a mid- oceanic ridge with new sea floor. The lesson continues to use models to explore different land formations at plate boundaries.
Formative Assessment #4: “Fault Line Performance Assessment” provides an opportunity for students to explain what they know about California landforms and movement along plates. The assessment includes; directions, task, and rubric for scoring.
In the previous lesson and performance assessment, students learned that different landforms develop on plate boundaries. Lesson 11 “Density of Granite and Basalt” returns students to how relative density of material (rocks) can predict how a dense oceanic plate will subduct under a less dense continental plate. Students explore the relative density of granite and basalt. When the two rock forms meet at a boundary the more dense basalt subducts.
Upon completion of the 11 lessons, students take a Post-Assessment to determine their overall understanding of the concepts presented in the unit.
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