Weathering Experiment

Pete Stelling
Western Washington University
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This project has students dirty several dishes equally and design experiments to determine which analogs of geologic processes are most efficient for removing the baked-on food. Students calculate rates of weathering and/or erosion, and compare these to actual rock weathering rates.

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This activity is used for an introductory Physical Geology course for non-majors/non-scientists

Skills and concepts that students must have mastered

Before assigning this project, students should have a basic understanding of the differences between chemical weathering, physical weathering and erosion. Additional knowledge of specific types of weathering will improve experimental design and interpretation and analysis of results.

How the activity is situated in the course

This project is a stand-alone, extra credit assignment that students conduct outside of class. I have found it important to discuss the results later with the entire class.


Content/concepts goals for this activity

Chemical weathering vs. physical weathering vs. erosion
Erosion/weathering rates
An understanding of Uniformitarianism (with regard to the effect of persistent geologic processes)

Higher order thinking skills goals for this activity

Developing analog models and evaluating the limits of the analogy
Experimental design
Evaluation of data
Simple calculations

Other skills goals for this activity

Description of the activity/assignment

After discussing weathering and erosion in class, students are asked to do a small amount of research on different types of chemical weathering, physical weathering, and erosion processes (mostly out of their textbook). Outside of class students then dirty at least four similar dishes with the same type, thickness and aerial extent of food, preferably baked on to ensure maximum stick. One dish is set aside as a control (no weathering or erosion will occur for that dish). For each of the remaining three dishes, students devise an experiment that mimics some sort of chemical weathering, physical weathering, or erosion process (freeze/thaw, sand abrasion, oxidation, etc.). Prior to the experiments, the thickness of food is measured. Experiments are timed, and at the end of the experiment each plate is turned over to determine how much which method removed the greatest aerial extent of food. Experimental results are compared to the control plate to determine the actual effectiveness. Erosion/weathering rates are determined by dividing the thickness of food removed by the experimental time. Students then calculate how long it would take to remove a pile of food the size of the Geology building (assume a 50 m radius sphere), and to remove an amount of food equivalent to the depth of the Grand Canyon. Students then compare these results to rock erosion and weathering rates, performing similar calculations using these "real" rates (see the full project description for details). Photos of each step and the scientists are encouraged in their 2-3 page writeup.

Determining whether students have met the goals

The assessment points I look for are:
1) Good experimental design
2) Appropriate geologic analogs
3) Correct calculations
4) Reasonable assessment of experimental errors and the limits of the analogy
5) Reasonable discussion of weathering/erosion type and rate involved in forming the Grand Canyon

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