Teaching geologic time and rates of landscape evolution with dice,

Katharine W. (Ruhl) Huntington

Massachusetts Institute of Technology

Summary

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. In this example, 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,while local examples are used to discuss landscapes as transient or steady over different time- and length scales. 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 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.

Dating and Rates, Landscape Evolution, Modeling/Physical Experiments, ...(more) | College Lower (13-14), College Upper (15-16)

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Context

Audience:

undergraduate: entry level

Skills and concepts that students must have mastered:

Context discussed as it varies for students in grades 9-16: see poster

How the activity is situated in the course:

Activities could be used in order together, or pulled out as stand-alone modules to complement another course.

Goals

Content/concepts goals for this activity:

Part 1: topography and landscapes, maps, 3-D visualization; Part 2: channel characteristics and sedimentary processes, landscape relief change; Part 3: radioactive decay, quantitative dating; Part 4: measuring quantitative erosion on landscapes, thermochronology, geotherms, isotherms

Geologic skills:

Higher order thinking skills goals for this activity:

Part 1: 3-D visualization; Part 2: experimental design and hypothesis testing; Part 3: graphing data and trends, interpreting graphs; Part 4: understanding rate measurements, plotting multiple variables (like heat, depth, and time) on the same axis.

Other skills goals for this activity:

Part 1: map skills, cross sections, GIS; Part 2: designing experiments and measuring stream characteristics in the field; Part 3: geologic applications of quantitative dating; Part 4: interpret thermochronologic data, relate measured rates to landscape change, case studies

Description of the activity/assignment

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).