Plate Tectonics in Three Dimensions: Lessons Learned

Plate tectonics is the foundational organizing paradigm of modern geology, and the backbone of most introductory college-level courses. It provides context for understanding geological features and processes across diverse topics, yet deep knowledge of plate tectonics comes from multiple scientific fields, making it a key example of convergent science. Instruction in plate tectonics thus provides challenges in helping students navigate complex intellectual territory. Many tectonic phenomena occur at plate boundaries, making them an obvious focus for instruction. We implemented Discovering Plate Boundaries as the first lab activity in undergraduate Physical Geology (required for engineering and Earth science programs), supported it with class lectures, and assessed its effectiveness through short-essay exam questions and problem sets with authentic data on earthquake and volcano locations. We find that the vast majority of students can define the surface expressions of plate boundaries, confirming that the activity addresses that learning goal. In contrast, the three-dimensional nature of subduction boundaries proved elusive to almost all students: they did not recognize that a slab was part of a plate with boundaries that could be drawn in the subsurface. These college-level results mirror our findings from middle-school classrooms, where a focus on plate boundaries at the surface in one school hindered students' three-dimensional thinking compared to a classroom that focused on convective movements. Despite the greater experience of our college students in calculus and physics, both of which employ three dimensional phenomena, the learning barriers were the same. We recognize that three-dimensional plate movement is particularly challenging to novice learners and is made even more difficult because the plate boundaries do not persist throughout the deep mantle. Our results show that additional attention must be paid to upper and lower plate boundaries in order for students to conceptualize them in totality.