BUILDING INSIGHTS INTO EARLY EARTH HISTORY AND DEEP PROCESSES WITH A HANDS-ON EXPERIMENT

Geology students are often confused by concepts like magma oceans, density layering, convection versus mantle plumes, and debates about the depth of penetration of subducting slabs because they are difficult to visualize. However, those concepts are key to understanding the early history of the earth and ongoing deep earth processes. Thus, we describe, here, a relatively simple experiment that lends itself well to building understanding of some deep earth processes. This experiment was developed by Nararro and Pena as part of an earth science class for high school science teachers who were instructed to develop lessons on density and viscosity that they could use in their classrooms. They created a density column with corn syrup, soy sauce, oil, and rubbing alcohol in a 1000 mL graduated cylinder. The viscosities of the different layers were demonstrated by injecting air bubbles into the base of the density column through a hose and observing how the rate of travel of the rising bubbles varied in the different fluids. An unexpected aspect of the experiment occurred when the air bubbles carried some of the dense syrup and soy sauce through the oil and into the alcohol layer where they mixed to form a fluid that was denser than the oil. The mixed layer sank through the oil but the fluids also separated from each other during the processes causing the lighter fluids to rise upward again. The motion caused by the mixing and separating of the different density fluids continued for some time and resulted in a highly visible plume in the center of the oil layer while the down welling fluids hugged the sides of the cylinder. The students were able to recognize the processes that occurred and could relate them to our earlier classroom discussions of magma oceans and mantle plumes.