How Students and Field Geologists Reason in Integrating Spatial Observations from Outcrops to Visualize a 3‐D Geological Structure

Abstract

Geologists and undergraduate students observed eight artificial “rock outcrops” in a realistically scaled field area, and then tried to envision a geological structure that might plausibly be formed by the layered rocks in the set of outcrops. Students were videotaped as they selected which of fourteen 3‐D models they thought best represented the geological structure and then explained their choice. The focus of this paper is on how students reasoned from observations to inferences. Students used observations of outcrops’ location, steepness (dip), orientation (strike), stratigraphy, and placement relative to topography to infer whether the structure was convex or concave, deep or shallow, symmetrical or asymmetrical, open or closed, and elongate or circular. On average, science majors produced more than twice as many evidence‐supported claims than did non‐science majors. Science majors produced more valid lines of reasoning than did non‐science majors, and students who selected a correct model produced more valid lines of reasoning than students who selected an erroneous model. Apparent challenges included identifying appropriate observational evidence, combining multiple lines of reasoning, and understanding the scale relationship between candidate models and the full‐scale structure.

Keywords:

• Argumentation
• Earth science education
• Geology
• Spatial learning
• Visual evidence

Acknowledgements

The authors thank the study participants for their thoughts and actions, G. Michael Purdy for permission to use the grounds of Lamont‐Doherty Earth Observatory, M. Turrin and L. Pistolesi for assistance with data acquisition, L. Pistolesi for preparing the illustrations, and the National Science Foundation (NSF) for support through grants REC04‐11823 to Kastens and REC04‐11686 to Liben. The opinions are those of the authors and no endorsement by NSF is implied. This is Lamont‐Doherty Earth Observatory contribution number 7230.

Notes

1. The word “visualization” in the context of science education has been used for several related concepts. Among the definitions that have been offered are: “a representation that has been placed in the public realm, in either a material object, visual, verbal, or symbolic form,” (Gilbert et al., 2008, p. 2), “a physical representation designed to make an abstract concept visible” (Reiner, 2008, p. 25), “the understanding of, the meaning attributed to, an internal representation” (Gilbert et al., 2008), and “the cognitive and brain processes associated with the act of visualizing” (Reiner, 2008, p. 25). To avoid ambiguity while remaining consistent with the other papers in this series, we will use the noun form “external visualization” to refer to a physical representation placed in the public realm, and the verb form “visualize” to refer to the process of forming a mental image. “External visualization” as we use it here is similar in meaning to “visual display” of Lynch (1990) and “external spatial representation” of Liben (2006, and references therein).

2. “Outcrop” is a place where solid rock is exposed at the Earth’s surface, emerging from beneath soil, loose sediment and vegetation.

3. “Strike” is the compass direction of the horizontal line that marks the intersection of an inclined plane with the horizontal plane. “Dip” is the angle in degrees between a horizontal plane and an inclined plane, measured down from the horizontal in a plane perpendicular to the strike.

4. In this paper, we use the geological terms “block diagram,” “strike/dip,” “antiform/synform,” and “stratigraphic/stratigraphy” for clarity of communication with the reader. None of these specialized terms was used with the participants.

5. “Stratigraphy” refers to the study of layered rocks, usually sedimentary rocks that were deposited flat lying at the Earth’s surface. A “stratigraphically lower” rock layer was deposited before a stratigraphically higher rock layer.

6. In examples cited from the participant’s protocols italics font represents participant’s gestures or actions; [square brackets] represent analyst’s explanation of the participant’s words; {curly brackets} represents analyst’s interpretation of participant’s reasoning.

7. In this paper, “concave” and “convex” refer to downward and upward departures relative to the Earth’s surface, i.e. relative to a local horizontal plane. Other reference surfaces are possible, for example, a cave is concave relative to the side of a mountain; the armpit is concave relative to the surface of the human body.

8. “Synform” is the geological term for structures that are concave upward, typically basins or parts of folds. “Antiform” is the corresponding term for structures that are convex upward, typically domes or parts of folds.

9. A “syncline” is a concave upward part of a fold in layered rocks. An “anticline” is a convex upward part of a fold. A syncline or anticline is described as “plunging” if the rock layers deepen along the axis of the fold. A well‐installed roof gutter is like a plunging syncline, plunging gently towards the downspout. Model M could be the “nose” of a plunging syncline and model N could be the nose of a plunging anticline.

10. During the pilot stage of this study, we asked participants to show us the shape of the geological structure by shaping a model from play‐doh or clay. The resulting models were crude, and unsatisfying to the participants themselves.

11. American Girl dolls 1:3; Barbie doll 1:6; Steiff classic Teddy Bear 1:6; Breyer model horses traditional series 1:9, classic series 1:12; Dollhouse standard scale 1:12; sandbox construction vehicles 1:16; toy soldiers standard scales 1:28 to 1:35; model airplanes, most common scale 1:72; model railroads HO scale 1:87; N scale 1:160 (Sources: Wikipedia articles on “Dolls,” “American Girl,” “Barbie Doll,” “Scale Model,” “Toy Soldier,” and “Brown Bear”; http://www.scalemodeltoys.com; www.steiffteddybears.co.uk; www.modelhorseguide.com).