Earth, Atmospheric and Planetary Sciences
Massachusetts Institute of Technology
Teaching geologic time and rates of landscape evolution with dice part of Rates and Time:GSA Activity Posters
Landscape evolution provides a convenient framework for understanding geologic time and rates because students can observe how processes like erosion and deposition shape their surroundings, even in urban settings. In order to describe landscapes qualitatively and quantitatively, students build 3-D sandbox models based on topographic maps and design and stage a "virtual adventure race." Sandbox landscapes are used to illustrate erosional processes, the role of water in sediment transport, relief change, and how erosion exhumes rocks from depth, while local examples are used to discuss landscapes as transient or steady over different time- and length scales. To convince students that the observed processes act over millions of years to shape Earth's surface, quantitative dating tools are introduced. Dice experiments illustrate radioactive decay and the shape of the age equation curve, and 14C dating, geochronology and thermochronology are introduced as "stopwatches" that start when a plant dies, a crystal forms, or a rock nears the surface and cools to a certain temperature. The sandbox model and thermochronometer "stopwatches" are combined to measure erosion rates at a point, uniform and spatially variable erosion, and rates of landscape change. Ultimately, model rates (cm/hour) calculated from stopwatch times on the order of seconds can be related to geologic rates (km/My) calculated from real million-year-old samples. SEE POSTER for detailed descriptions of each activity in Parts 1-4 (complete with specific Learning Goals, Context, Materials, Activity Summary, Evaluation, and adaptation to challenge students in grades 9-16).