VISUALIZING A 3-D GEOLOGICAL STRUCTURE FROM OUTCROP OBSERVATIONS: STRATEGIES USED BY GEOSCIENCE EXPERTS, STUDENTS AND NOVICES

We have investigated how people with a range of expertise (undergraduate non-science and science majors, geoscience graduate students, and structural geologists) observe a set of scattered outcrops, and then visualize a 3-D structure that could plausibly be formed by those outcrops. We used 8 plywood “artificial outcrops,” positioned so as to form a 200m long elongate basin. After brief instruction, we led individual participants to each outcrop in a predetermined order. Participants had blank paper, pencil, and clipboard, but no map or compass. After observing the outcrops, participants chose which of 14 scale models they thought best represented the shape of the structure, oriented the model to align with the full-scale structure, and explained their reasoning. Choices and explanations were videotaped for later coding.

All experts and most advanced students recorded their observations onto the blank paper in the form of a map or map-like representation. As they observed each outcrop, they scanned their surroundings for landmarks and observed spatial relationships among outcrops. In contrast, most novices did not approach this task spatially. They focused on only the single outcrop in front of them at the moment, did not look back or around, and recorded their observations on the paper in the top-to-bottom order that is conventional for text. Less experienced students generally made accurate observations, but these were imperfectly matched to the needs of the task: they painstakingly recorded irrelevant information (e.g. presence of bushes), while failing to note essential information (e.g. which way the layers were slanting). Experts began to develop a spatial hypothesis about the shape of the structure after observing the first few outcrops, which they then tested at subsequent outcrops; inexperienced students did not express a spatial hypothesis until confronted with the scale models. At all levels of expertise, participants neglected the interaction between topography and structure, which led them to incorrectly dismiss one plausible model. In summary, many participants' difficulties with the task seem rooted in their failure to perceive or record the kinds of spatial information necessary to solve the posed problem, rather than in their difficulty integrating the spatial information in hand.