Using Student-Generated Models to Understand Plate Tectonics BY RON GRAY, ALLYSON ROGAN-KLYVE, AND BRITTEN CLARK-HUYCK
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he importance of engaging students in scientific modeling has been well established and features prominently in the Next Generation Science Standards (NGSS Lead States 2013). Engaging students in this practice provides an authentic science experience; it also helps students make sense of the world around them (Krajick and Merritt 2012). We view scientific models as more than just representations of a natural phenomenon; they are tools with which students make sense of phenomena (Passmore, Svoboda, and Giere 2014). In this unit, we wanted students to be able to use their own models as tools for constructing a scientific explanation of a particu-
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lar phenomenon, rather than as simple representations of the phenomenon. A key step in designing these learning experiences was selecting an appropriate natural event that could serve as the anchoring phenomenon for the unit. We selected a puzzling phenomenon that would necessitate students gaining a strong understanding of the theory of plate tectonics and associated concepts and that would be engaging and relevant to their lives. Our location in the Pacific Northwest and proximity to the “ring of fire” gave us a number of options to consider. However, in an effort to connect with ongoing and current scientific work, we selected Axial Seamount as our anchoring phenomenon.
CONTENT AREA Earth science; integrated science
GRADE LEVEL 6–8
BIG IDEA/UNIT Plate tectonics ESSENTIAL PRE-EXISTING KNOWLEDGE Continental drift
TIME REQUIRED 11 (55-minute) class periods
COST None
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Scientific background
| FIGURE 1: Position of Axial Seamount
WIKIMEDIA COMMONS
Axial Seamount is an underwater volcano located on the boundary of the Juan de Fuca and Pacific plates, about 300 miles off the coast of Oregon (see Figure 1). It is very active and well-studied, with documented eruptions in 1998, 2011, and 2015. Axial Seamount is located along a divergent boundary, which is why the volcano is so active. Given Axial’s proximity to our geographic location, the availability of rich and current scientific content about the volcano, and the likely interest of our students in this phenomenon, Axial seemed to be an excellent topic to anchor our unit.
Lesson sequence The main goal of this unit was to engage students in the practice of modeling to construct a valid scientific explanation of the existence of Axial Seamount through the theory of plate tectonics. We introduced Axial Seamount through a video news clip about the recent eruption and a series of datarich activities developed by the New Millennium Observatory (NeMO) project, which reveal the volcanic nature of the seamount (see Resources). The four NeMO activities were conducted using a group jigsaw approach over two class periods. Although these activities are engaging, it is possible to begin the unit as we do below without using them by simply starting with the concept that Axial is a volcano. After completing these activities, students were ready to begin creating explanatory models that would help them make sense of this natural phenomenon. The following provides a day-by-day overview of the activities we used with students to help them co-construct models with their peers to understand the cause of the underwater volcano.
Day 1 Having introduced Axial, we began by asking the driving question: How did Axial Seamount come to be where it is today? Through facilitated discussion, we elic-
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ited students’ initial ideas (e.g., “What do you see going on here?” and “What do you think caused the volcano to form here?”) on poster paper in the front of the room. We then broke students into small groups of three or four to co-construct initial conceptual models to answer the driving question. Each
Exaggerated swatch bathymetry of Axial Seamount. NOAA
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group drew a conceptual model on poster paper and presented its model to the class through a facilitated share-out session (see Figure 2a for an example of a student group’s initial model). By the end of the first day, students’ ideas had been elicited and were active resources (Campbell, Schwarz, and Windschitl 2015) for the class to reason with as we transitioned to the data-rich activities that would build their understanding of plate tectonics in relation to Axial Seamount.
examining patterns in earthquake data, groups were able to outline Earth’s tectonic plates and look specifically at the area of Axial Seamount to discover that it sits on a plate boundary. We then examined the various types of plate boundaries that exist and their associated geologic effects. Building on the previous earthquake map, groups added major mountain ranges and volcanoes to their world maps and placed arrows along boundary lines to predict the direction of plate motion.
Days 2 and 3
Days 4 and 5
After reviewing their initial models and the driving question, student groups investigated the relationship between earthquakes and plate boundaries by mapping recent data on a world-map handout (see Resources for source of recent earthquakes). Through
To determine the type of fault at Axial Seamount, we discussed Earth’s magnetic-field reversals and the ways in which they affected seafloor rock formation. We also talked about the role of radiometric dating. Students examined paleomagnetic
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| FIGURE 2: Examples of initial (a), revised (b), and final (c) student models a
b
c
data sets (see Resources) across the globe and then specifically at the Juan de Fuca and Pacific plate boundary. By examining these data, students were able to uncover patterns of geologic features based on the plate boundary type (e.g., terrestrial volcanic ranges occur at convergent boundaries). Most importantly, the ages of rocks increase as they move away from the boundary, revealing that Axial Seamount lies at a divergent plate boundary. Using their previous understandings of plate boundary types, students were able to label the boundary as divergent.)
Days 6 and 7 To provide students with a more complete understanding of plate tectonics, we asked groups to zoom out from our focus on Axial Seamount and investigate the boundary on the other side of the Juan de Fuca plate, where it meets the North American plate. To investigate the boundary, we provided paleomagnetic data (see Resources) and earthquake depth data. Using their previous understandings of plate boundary types, students were able to label
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the boundary as convergent (student’s notes available with this article’s online supplements; see Resources). Further, the earthquake depth data (available with this article’s online supplements), when graphed by students with longitude on the x axis and depth on the y axis, revealed the angle of subduction at the continental margin, or the Cascadia subduction zone. After this series of activities, groups were able to complete their first model revision with their new understanding: Axial is at a divergent plate boundary (see Figure 2b).
Days 8 and 9 Through a discussion reviewing the evidence so far, students realized that they still lacked a sufficient mechanism to explain plate movements. During a
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class brainstorming session, we collected a number of possible causes for plate movement, which we used as keywords to guide student internet research to support or refute these explanations. Through this activity and facilitated small- and wholegroup discussion, students were able to identify the process of convection, driven by energy from radioactive decay of elements in the Earth’s core, as a primary mechanism. Students further revised their previous models to include their new understandings of subduction and convection (see Figure 2c).
Days 10 and 11
| FIGURE 3: Checklist for final explanation Evidence
Checklist
NeMo data
Axial is a volcano.
Earthquake data and magnetic data
It’s at a divergent plate boundary (Juan de Fuca and Pacific).
Earthquake depth data
There is a subduction zone on the other side of the plate.
Earthquake data
Subduction zone causes earthquakes and volcanoes (e.g., Mt. St. Helens).
Cascade volcanoes Earthquake data
Earth’s crust is broken into plates that “float” on magma.
Web hunt Web hunt
Decay of radioactive material in the core causes convection currents to move the plates.
Students now had a complete model that helped them underincluded in the final explanation and the evidence stand why Axial Seamount is located where it is. supporting it (see Figure 3). With this support, most We facilitated groups in devising a testable hystudents were able to create a final, written explapothesis based on their model, and they searched nation that drew upon their understanding of plate for evidence to support or refute their hypothesis. tectonics to account for the presence and location of For example, some students thought, “If Axial SeaAxial Seamount (an explanation rubric is available mount is formed at a divergent boundary, then we with this article’s online supplements) with some should see the same pattern of rock ages and magsupport (as described below). netic reversals at other underwater seamounts.” This hypothesis can be tested using the available evidence and by examining the Supporting student geologic features of other seasense-making mounts in Google Earth. throughout the unit We concluded this unit by reThe sequence of activities quiring that each student write From the variety of initial stuwas designed a final, evidence-based expladent models, it was clear that to help students develop nation for why Axial is located students had a number of difa more robust scientific where it is, based on the final ferent explanations for why explanation that models their groups had creatAxial is in its current location. they could support ed (see an example explanation The sequence of activities was with multiple types of with this article’s online suppledesigned to help students dements). We chose first to cogenvelop a more robust scientific evidence. erate with students a checklist explanation that they could with the key elements to be support with multiple types of
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| FIGURE 4: Summary table, formed intermittently during the unit Activity
What we learned
Mapping earthquakes
The crust is broken into plates. Earthquakes occur at the edges of the plates and show us where they are.
Axial is on a plate boundary!
Magnetic and radiometric data
The Earth’s magnetic field reverses, which affects rocks that are newly formed. By looking at the ages and magnetic direction of the rocks at a plate boundary, we can tell which way they are moving (divergent, convergent, transform).
Axial is at the boundary of the Pacific and Juan de Fuca plates. Data shows they are diverging (moving apart), lifting magma up to the surface to form Axial.
Earthquake depths activity
Juan de Fuca plate is converging with the North American plate. Juan de Fuca is subducting under the North American plate, causing earthquakes and volcanoes on land. The subducting plate is melted in the mantle.
The seafloor created at Axial is eventually “recycled” at the Cascadia subduction zone.
Mechanism web hunt
The magma in the mantle slowly flows in convection currents under the plates, causing them to move. The energy for this is from the decay of radioactive elements in the core.
Convection currents are causing the Juan de Fuca and Pacific plates to diverge, releasing the magma that formed Axial.
evidence. This proved to be a fairly complex task for most students, and we found that a number of strategies to support them in this work were needed. A key strategy was having students work together in small groups of three or four. Such groups allowed students to negotiate ideas with their peers and provided an opportunity to use new information to revise their previous models. This led to a general class structure of working on activities or problems in small groups before coming back to whole-group discussions for consensus building. We found this pattern helpful for promoting student understanding. Working in small groups also allowed us to better under-
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How it helps us explain Axial Seamount
stand what sense students were making of the phenomenon. Throughout the unit, the scientific models were developed, revised, and tested in these small groups. They were readily available to groups each day of the unit and were often referenced by the teacher. This allowed the models to be used as tools for group sense-making about the phenomenon. Once the model was revised and tested, they were vital resources for students as they constructed their individual evidence-based explanations. Additionally, class share-out sessions, during which we facilitated small groups’ presentation of their models and follow-up questions and discussion, were fruitful for students’ learning from each
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other and our ongoing formative assessment of student understanding. We also used these sessions to talk explicitly about scientific modeling and the role it plays in science, further helping students understand the work they were doing and why it is an authentic practice of science. Although making use of small groups was helpful, we also found it necessary to create a number of scaffolds for students to successfully engage in this complex task. For example, we used a whole-class summary table after each activity (see Figure 4). This allowed the class to come to a consensus on what they learned and how their new knowledge added to their explanation of the Axial Seamount phenomenon. As a whole-class public record, the summary table remained visible throughout the unit as a resource for students. These scaffolds, along with probing questions, and exit passes, served as formative assessments throughout the unit. Additionally, scaffolding students’ final, written explanations was essential. Precisely how you go about scaffolding your students’ writing depends on their familiarity with writing evidence-based explanations. We also supported their writing by examining with students examples of other evidence-based explanations we had created about topics of previous units.
Conclusion Using a local geological feature likely to be of interest to our students allowed us to introduce a puzzling phenomenon that could be the basis of the construction of explanatory models. We suggest finding a local geologic phenomenon (e.g., the Hawaiian archipelago, the Yellowstone caldera) to increase this unit’s relevance to your students. By engaging students in scientific modeling, we
helped students not only make sense of the specific phenomenon of Axial Seamount but also develop a robust understanding of the theory of plate tectonics and its related concepts.
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REFERENCES Campbell, T., C. Schwarz, and M. Windschitl. 2016. What we call misconceptions may be necessary stepping-stones on a path toward making sense of the world. Science Scope 39 (7): 19–24. Krajcik, J., and J. Merritt. 2012. Engaging students in scientific practices: What does constructing and revising models look like in the science classroom? Science Scope 35 (7): 6–10. National Governors Association Center for Best Practices and Council of Chief State School Officers (NGAC and CCSSO). 2010. Common core state standards. Washington, DC: NGAC and CCSSO. NGSS Lead States. 2013. Next Generation Science Standards: For states, by states. Washington, DC: National Academies Press. Passmore, C., J.S. Gouvea, and R. Giere. 2014. Models in science and in learning science: Focusing scientific practice on sense-making. In International Handbook of Research in History, Philosophy and Science Teaching, ed. M.R. Matthews, 1171–202. Netherlands: Springer.
RESOURCES Axial Seamount blog—http://bit.ly/1JfAgVo Cosmos News report on Axial Seamount eruption—http://bit. ly/295IUcL New Millennium Observatory (NeMO)—http://bit.ly/2agm5J3 New Millennium Observatory (NeMO) Curriculum—http://bit. ly/29Tvenv NOAA: Axial Seamount—http://bit.ly/29Tw1Vi Online supplemental files for this article—www.nsta.org/ scope1609 Paleomagnetic data—http://bit.ly/29THOXI Subduction zone earthquake data—http://bit.ly/29efvRo USGS Earthquake Hazards Program: Recent Earthquakes (change settings to: 30 Days, Magnitude 2.5+ Worldwide)—http://on.doi.gov/1GhKUIj
Ron Gray (
[email protected]) is an assistant professor of science education in the Center for Science Teaching and Learning at Northern Arizona University in Flagstaff, Arizona. Allyson Rogan-Klyve is an assistant professor of science education in the Department of Science Education at Central Washington University in Ellensburg, Washington. Britten Clark-Huyck is a science teacher at Corvallis High School in Corvallis, Oregon.
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Connecting to the Next Generation Science Standards (NGSS Lead States 2013) • The chart below makes one set of connections between the instruction outlined in this article and the NGSS. Other valid connections are likely; however, space restrictions prevent us from listing all possibilities.
• The materials, lessons, and activities outlined in the article are just one step toward reaching the performance expectations listed below.
Standard MS-ESS2: Earth’s Systems www.nextgenscience.org/dci-arrangement/ms-ess2-earths-systems
Performance Expectation MS-ESS2-2. Construct an explanation based on evidence for how geoscience processes have changed Earth’s surface at varying time and spatial scales.
DIMENSIONS
CLASSROOM CONNECTIONS
Science and Engineering Practices Developing and Using Models
Students construct initial, revised, and final models to show how Axial Seamount was formed.
Analyzing and Interpreting Data
Students analyze and interpret multiple data sets, including earthquake and radiometric data. They also determine which data to collect and analyze as they test their final models.
Disciplinary Core Idea ESS2-A. Earth Materials and Systems
• The planet’s systems interact over scales that range from microscopic to global in size, and they operate over fractions of a second to billions of years. These interactions have shaped Earth’s history and will determine its future.
Students discover the cycling of oceanic crust through mapping the Cascadia subduction zone and examining patterns in radiometric dating of the seafloor.
Crosscutting Concept Patterns
Students discover plate boundaries through mapping recent earthquakes.
Connections to the Common Core State Standards (NGAC and CCSSO 2010) ELA CCSS.ELA-LITERACY.WHST.6-8.2: Write informative/explanatory texts, including the narration of historical events, scientific procedures/experiments, or technical processes.
Mathematics CCSS.Math.MP.2: Reason abstractly and quantitatively.
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