Density, Isostasy, and Topography

Anne Egger, Central Washington University.

This page is a supplement to the original activity description found here

Short description of the activity:

In this activity, students develop an explanation for the bimodal topography of the earth through measuring densities of rocks and wood blocks, deriving the isostasy equation, and applying their knowledge to estimate crustal thicknesses.

How does this activity lend itself to teaching the methods of geoscience?

This activity highlights several techniques that geoscientists use to conduct investigations, and it is easy to highlight them in discussions. First, we start the activity by looking for patterns in spatial data: global topography. Both the scale and pattern seeking are important geoscientific thinking skills. Second, we use analogous materials in experiments since Earth materials deform over longer time scales than can be replicated in the classroom or laboratory. Third, we share data because it is not possible for each student to collect all of the data, and that process also allows students to evaluate each others' data. Finally, data are used to derive a mathematical model for isostasy, which the students then use to make predictions about the Earth. A critical component of this activity is making each of these concepts explicit in the activity.

Specific Adaptations: How do these help the activity address the methods of geoscience?

There are no specific adaptations to make to the activity, other than to be sure to highlight in discussion the points described above and how the tasks within the activity mimic the real processes that geoscientists use to study the Earth.

Assessment: How are the methods of geoscience assessed?

The current assessment activity focuses on the students' understanding of the relationship between topography and isostasy and how they change over space and time. I would add another prompt to the assessment to ask students to articulate how the methods used to study these relationships differ from what they have learned about the "scientific method".