Grand Canyon Cross Section Lab

High school Earth Science class

This exercise assumes no prior knowledge or skills. The tutorial slides (see below) explain the concepts of geologic maps, cross sections, and core samples.

This is a stand-alone exercise.

The goal of the this activity is to activate students' spatial thinking in order to facilitate deeper understanding of the structure of Earth's shallow subsurface.

Students will make a spatial prediction, receive feedback, and modify their prediction based on the feedback.

This activity is not necessarily expected to solve students' problems with spatial thinking about subsurface patterns. Rather, it is a tool for teachers to identify students' misconceptions and begin to discuss and address concepts related to the Laws of Original Horizontality and Lateral Continuity.

Not applicable.

Science of Learning: Why It Works

Despite the importance of spatial understanding in geoscience and other STEM disciplines, it is a skill that is not often directly addressed in schools. However, there is abundant evidence that spatial understanding can be taught and retained (e.g., Newcombe and Shipley, 2015, Baenninger and Newcombe 1989, Ben-Chaim, Lappan, and Houang, 1988, Lord, 1985, Smith and Litman, 1979) and that practicing spatial skills leads to improvement in STEM fields (McGee, 1979, Cohen and Hegarty, 2012). It has also been shown that spatial visualization activities soften the gender difference in ability (Newcombe, 2013, Newcombe and Shipley, 2015, Baenninger and Newcombe 1989, Ben-Chaim, Lappan, and Houang, 1988, Lord, 1987, Smith and Litman, 1979).

Extensive research has focused on the benefits of sketching as a way of learning about 3D spatial concepts and diagrams (Gagnier et al., 2017, Yin et al., 2010). We designed this Project Based Learning (PBL) lesson based on the assumption that improving understanding about subsurface features engenders "penetrative thinking," which is a useful spatial skill in STEM disciplines. In fact, although there are strong theoretical and empirical foundations supporting this activity, it is also an interesting PBL lesson (Hmelo-Silver, Golan-Duncan, & Chinn, 2007). Our classroom implementations of this activity suggest it promotes appreciable improvement of penetrative thinking in high school Earth science students.

When students engage in predictive sketching, they create an external representation of their conceptual model which can be used to evaluate student's conceptual understanding and aid in determining what students might be struggling with as a class or individually. Importantly, this activity provides students with a way to correct their conceptual model. It is also worth noting, drawing increases motivation and engagement (Ainsworth et al., 2011). Feedback can further improve student's understanding by providing information that can be used to check correctness of the sketch (Hattie & Timperley, 2007). This allows students to analyze where they went wrong and understand how to fix their model.

In Part 1 of the activity, question prompts ask students to determine what the colors represent in the map provided. The students then draw their initial interpretation of the subsurface cross-section using a topographic and geologic map of part of the Grand Canyon tilted so North is clear and towards the right of the page, and coordinates are provided to show the location. Students also answer questions about what the colors represent with reference to specific layers and where the highest and lowest points are. These questions are asked for every cross-section sketch.

In Part 2, question prompts ask students to compare their original cross-section to the core samples provided before sketching the cross-section again, and how these new data influenced their revisions. The core samples provide data on depth and thickness of each rock layer for students to use to revise their cross-section sketch. The cores come from the cross-section, one on each side of the river, to compare and revise their cross section. Ideally, students would mark the depths of the layers in their cross section at the approximate location of the core sample, keeping the relative thickness in mind when marking off where each bed starts and ends. This data should provide a larger and more accurate 3D view of the cross section.

In Part 3, students mark where gold is exposed on the surface of the canyon based on the location of the layer it is found in. Ideally, by the time students reach Part 3, they will have sketched horizontal layers. Here we check students understanding of the 3D nature of the layers after having provided information about the depth and orientation of the layers. Students also explain their reasoning for where they expect gold to be found at the surface. They should mark the space where the layers of the Supai Group and the Redwall Limestone meet are exposed at the surface of the canyon. If a student colored the whole cross-section where these two layers meet, it would be incorrect because the inner parts of the cross section are not exposed and the instructions state that students need to mark where it is exposed at Earth's surface. Additionally, students should only mark the left side as there was only gold observed in Core Sample 1. Any other location identifications are incorrect.

Part 4 is broken down into Part A and B. In Part 4A, students are asked to compare an image of the Grand Canyon to our sketches. In comparing their understanding with what the region actually looks like and seeing the depth of the Grand Canyon and the layers from a cross-section outcrop perspective can encourage a deeper understanding of penetrative thinking, one of the spatial skills supported in this project-based lesson. In Part 4B, students are asked to draw a connection between a fundamental law of geology, The Law of Original Horizontality, and their cross sections. This law states that the rock layers we see today were originally deposited horizontally and any deformation must have occurred at a later point in the rock forming process. This connection is meant to highlight the reason behind why all these layers are meant to be drawn horizontally stacked on each other. Furthermore, this is a real law of geology that experts consider and therefore it is important for novices to be introduced to this in a setting where it clearly applies. Additionally, and based on the universal nature of this law, students would take a step back from the sketching to realize this occurs globally and realize that it does not just apply to this cross section, but also the layers currently below them, which would further connect the activity to their everyday life.

Teaching materials:

• Grand Canyon Cross Section Tutorial slides (PowerPoint 2007 (.pptx) 16.2MB May29 19)
• Grand Canyon Cross Section Lab - student handout (Acrobat (PDF) 3.6MB May29 19)
• Grand Canyon Cross Section Lab - notes on PlayDoh models (Microsoft Word 2007 (.docx) 2.8MB May29 19)
• Grand Canyon Cross Section Lab - example of answers with vertical layers (Acrobat (PDF) 4.7MB May29 19)
• Grand Canyon Cross Section Lab - example of answers with horizontal layers (Acrobat (PDF) 4.8MB May29 19)

The lesson duration over the entire four parts is about 50-60-minutes. In Parts 1 and 2, where students draw their initial interpretation of the subsurface and reflect on this interpretation via new data, teachers should attend to how students are using this data as feedback to revise their understanding. Teachers should also be mindful that by the time students reach Part 3, they should have the subsurface represented as horizontal layers. Part 4 is the final opportunity for students to use additional feedback to construct an explanation of the subsurface and connect their understanding to the Law of Original Horizontality. Teachers should prompt students to reflect carefully about their final explanations in order to promote a more scientifically-accurate understanding.

The activity provides many formative assessment opportunities for teachers, including drawings that reveal students' thinking about the subsurface, as well as open-ended questions that prompt students to construct explanations about the subsurface. In both cases, teachers can compare students' responses to scientifically accurate modes of thinking and explanation to evaluate their understanding.

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