VISUALIZING EARTH’S INACCESSIBLE INTERIOR – WHAT WORKS FOR STUDENTS?

Whether a novice or expert in the geosciences, we are frequently challenged to visualize and mentally manipulate portions of Earth we cannot touch or examine first hand. Our knowledge of the details of the Earth’s interior is based on indirect evidence. Much of this evidence is based on seismic waves, invisible to our eyes and magnetic and gravitational fields imperceptible to our touch. On rare occasions, experts have an opportunity to study rocks that provide a view into Earth but these same rocks often have little meaning for the novice learner in geosciences. So how do we help students learn about Earth’s interior? Analogies, simulations and animations are commonly used tools in teaching geosciences. However, we have little evidence of how well these techniques work in the classroom and anecdotal evidence suggests that these techniques can be problematic.

Students often enter an introductory geology course with misconceptions of how Earth works and unfortunately, all too often, they leave with these same ideas firmly in place. Many of the common analogies propagate alternative conceptions such as the mantle is molten. We tell students that the rigid plates ‘float’ like rafts on the asthenosphere and that the mantle convects like a pot of boiling liquid. We often use the color of red – like hot molten lava – in cross sections showing seismic velocity variations in the mantle. The students know that the magma forming volcanoes comes from melting of the mantle but they do not know how little of the mantle is actually melted. While expert instructors qualify these analogies telling students that these processes occur over millions of years, and that the melt percent in the mantle is extremely small, the novice geoscience student often does not build these constraints into their mental models of Earth’s interior.

In seismology, we have the challenge of teaching the basics of seismic waves, something very abstract. Rocks breaking generate seismic waves, but why and how do they travel in solid rock? One of the most common visualization tools used to demonstrate wave propagation in the Earth is a computer simulation by Alan Jones called Seismic Waves. In my presentation, I will discuss the challenges of using simulations like this to help students dispel alternative conceptions about Earth and how waves propagate.