Evidence for Plate Tectonics
In this lesson, students will attempt to piece together cut-outs of the present-day continents based on ‘dinosaur fossil’ clues to recreate Pangaea. The students will then color and order a series of pictures to create a flip book of the probable course the continents drifted in the past to illustrate continental drift. The teacher will also demonstrate the mechanism of seafloor spreading. These ideas (continental drift and seafloor spreading) will provide background knowledge for the theory of plate tectonics.
The theory of plate tectonics states that the Earth’s crust and part of the upper mantle (together, the lithosphere) are broken into sections called plates which move on the plastic-like layer known as the asthenosphere. Convection currents in the mantle are thought to be the cause of plate movement. The movement of Earth’s lithospheric plates causes major geological events like earthquakes, volcanic eruptions, and mountain building (GLCEs, pp. 69)
To develop the theory of plate tectonics, the ideas of continental drift and seafloor spreading were combined. Alfred Wegener first suggested that the present-day continents were joined into a super continent known as Pangaea, and that they moved over millions of years into their current positions. Fossils, climatic evidence, similar rock structures, and the way the continents fit together like a puzzle support the idea of continental drift. Despite the fact that Wegener could not explain how the continents moved at that time, later mapping of the ocean floor and magnetic evidence supported the idea that the seafloor was spreading, which was the method by which the Earth’s crust, and thus continents, could move (Earth Materials and Processes, pp. 98-119).
- E.SE.06.51 Explain plate tectonic movement and how the lithospheric plates move centimeters each year.
- Explain how continental drift and seafloor spreading support tectonic plate theory.
Presentation materials (Overhead transparencies or PowerPoint presentations, etc):
Copied materials (Handouts, worksheets, tests, lab directions, etc.):
- Pangaea puzzle handout (per pair)
- Pangaea flip book worksheet (per student)
- Developing a Theory worksheet (per student)
Pages in textbook: Book: Glencoe Science: Earth Materials and Processes Pages: 98-105
For the teacher or the class as a whole:
- Colored pencils/markers
- Paper for seafloor demonstration
For each laboratory station:
- One envelope containing a Pangaea puzzle
INTRODUCTION (5-10 MINUTES)
- (3 min) Students will have previously read the first two sections of Chapter 4 about continental drift and seafloor spreading (pp. 98-105), and recorded three things they learned from each section. When they enter, the students will pull out the facts they recorded and share them with their seat partner.
- The teacher will have several students share what they learned from each section with the class which will be recorded on the overhead.
- The teacher will explain that the class will be completing several activities to illustrate the ideas that they read about.
MAIN TEACHING ACTIVITIES (35 MINUTES)
- (3 min) Students will complete the Pangaea puzzle (handout attached) with their seat partner using the dinosaur fossil clues. The teacher will assist the students and monitor their progress. Assistance questions could be:
- What clues did you use/are you using to put the continents together?
- How did Alfred Wegner put the continents together using clues? Did he find patterns or match anything?
- Show me how you pieced together the puzzle. Are your fossil clues matching?
- The pieces fit, but the dinosaur and plant fossils on these two continents are not matching. How could you make them match?
- The teacher will lead a short class discussion, asking students to volunteer how they arranged the continents and how/why they arranged them that way.
- Once the discussion is over, the students will be instructed to return their Pangaea puzzle pieces to the envelope and turn it in at the front of the class.
- Each student will receive a Pangaea flip book worksheet. They will then color each continent a different color across every frame, each of which shows the probable position of the continents at some number of millions of years ago. After coloring, they will determine the order of the frames, starting at Pangaea and ending at the present day, based on the positions of the continents in each frame. Once the pages are in order, the students will bind the pages together to create a Pangaea flip book. At this time, the teachers will be moving around the classroom and assisting the students as needed. The teachers can assess the students’ understanding of continental drift and how the Earth’s surface has changed by monitoring the students’ efforts to create the Pangaea flip books and by asking them questions like:
- Getting started: What is Pangaea? If the continents started as the supercontinent Pangaea, how do you think they must have moved to become spread out like they are today?
- How are you figuring out the order of the frames?/Why did you decide to put the frames in that order?
- How does your flip book show continental drift?
- What do you think caused the continents to move?
- After the students have spent approximately 10-15 minutes on the Pangaea flip book, half the class will be gathered to look at another piece of evidence for the theory of plate tectonics: seafloor spreading.
- The teacher will explain seafloor spreading and demonstrate one “round” of expansion, before calling up students to color in the subsequent “rounds” via the following:
- Magma from inside the Earth’s crust rises up through cracks in the ocean floor (four strips of paper spread out from a center point).
- The metal in the magma aligns with the Earth’s magnetic pole (draw colored arrows going the same direction on the four strips of paper).
- Many, many years later, more magma rises up from inside the Earth and creates new crust on the seafloor, again the metal aligns with Earth’s magnetic field (show how this pushes the other floor out – it spreads – and draw in arrows).
- Then, the magnetic pole of the Earth changes, so when the magma rises up again, the metal changes how it aligns (draw colored arrows going the opposite way on the strips).
- The other half of the class will be invited to watch the demonstration while the first half returns to working on their Pangaea flip book.
CONCLUSION (5 MINUTES)
- Any Pangaea flip books not finished will be finished for homework. The students will be given a worksheet with three questions about continental drift, seafloor spreading, and how these ideas support the theory of plate tectonics.
Explain how continental drift and seafloor spreading support tectonic plate theory.
RUBRIC FOR GRADING
An excellent response to the embedded assessments would be a Pangaea puzzle pieced together correctly using fossil clues, and a Pangaea flip book in the right order with the continents colored-coded correctly across all frames.
An excellent response to the formal assessment questions would be:
1. What is continental drift? Give two types of evidence that support it.
Continental drift is the idea that the continents have moved over time. Fossil clues of plants and animals; climate clues (warm-weather fossils, glacier evidence); rock structures/clues; puzzle-like fit of the continents are types of supporting evidence.
2. Earth’s magnetic pole changes throughout history. What evidence supports this?
Rocks on the seafloor by mid-ocean ridges have switching magnetic fields/readings (“magnetic reversal”).
3. According to tectonic plate theory, the Earth’s crust and upper mantle are broken into sections that can move. What two ideas support this theory?
Continental drift and seafloor spreading.
Created together with Elizabeth Cusick.