This activity is used in an introductory oceanography or geology course for non-majors. The class meets once a week and does not have a lab component, so this activity is used to break-up the 3 hour lecture period.

The students must have an introduction to of the composition of each of the layers of the Earth and a basic understanding of plate tectonics. However a comprehensive understanding of these concepts is not necessary. Students also need a conceptual understanding of density and how to calculate it based on mass and volume.

This exercise is placed in the middle of the first lecture on earth materials and plate tectonics. This activity is used to solidify the concept of density and leads into a discussion on isostacy.

Density calculations, basic rock identification, composition and density of the layers of the Earth

Formulation and evaluation of a hypothesis

Group collaboration and data sharing

This activity modifies a typical density laboratory exercise to fit within a lecture session. Students are asked to compare the densities of six different rocks/minerals collected from six different environments. Based on the brief description of each rock the students are asked to first predict which rock has the highest density and which rock has the lowest density. The students are then asked to construct a hypothesis and test their hypothesis by calculating the density of the rocks. Students are then asked to apply information from lecture to place each rock in the appropriate layer of the Earth.

Student Handout for Density Assignment (Microsoft Word 120kB May31 13)

This exercise was modified from a typical laboratory exercise to be used in a lecture setting rather than a lab setting. Therefore, I provide the mass and volume of all the rock samples after they class has finished with their hypotheses. Depending on your classroom resources and time availability, you may want to have them measure these properties themselves. Due to time constraints, I also only require each group to complete two density calculation and then record the densities on the board. Each group is then required to answer the remaining questions.

The version that I have posted here uses very generic rock descriptions, however if you know where your rock samples were collected, you could use more specific descriptions. For example, I have used granite collected from the Sierra Nevadas and basalt collected from the Juan de Fuca Spreading Center.

I typically use an andesite for the mystery rock. Of course, any granite or rhyolite would work as well. I don't use an ocean crust sample because all basalts look very similar and the students would probably be able to guess where it came from just by looking at it.

I observe the group discussions during class and try to address any misconceptions immediately. I also collect and grade the lab handout.