Evaluating the lines of evidence for plate tectonics

• Students will identify patterns related to continental shapes, till distribution, and fossil distribution.
• Students will identify several physiographic features on the ocean floor.
• Students will determine age distribution of the oceanic crust.
• Students will determine marine sediment thickness distribution.
• Students will observe patterns between these physiographic features, oceanic crust ages, and marine sediment thickness.
• Goals and skills include map reading and interpretation, synthesis of multiple data sets, pattern identification, and oral communication in the context of group work.

Methods of Geoscience

The overarching geoscience methods inherent in this activity are analyzing maps and identifying patterns among multiple datasets. In addition, some instructors may choose to intersperse short discussions throughout the activity about how the data were obtained that highlight geoscience methods. This could include identification of glacial features and deposits in the field; sampling and dating techniques to determine absolute ages of rocks; sediment sampling procedures; and instruments used to characterize the physiography of the ocean floor.

This activity is appropriate for an introductory-level geology or oceanography course. It should be situated in the curriculum before the concepts of continental drift and plate tectonics are discussed. I generally use this activity (or a modified version) in a lecture course or during the lecture portion of a lecture/lab course as an in-class exercise, but it could easily be expanded or included as a component of a plate tectonics lab exercise. No special equipment is necessary, but each student needs to be given a preparation exercise one class meeting in advance, including maps of whichever scientific specialty he/she is assigned.

The necessary materials include a preparation exercise, handout, and color maps for each student. The preparation exercise should be distributed one class meeting in advance and asks students to do some reading in their textbook and come to class prepared to teach other students in the class about some geologic data. Students will receive one of three preparation exercises, each with a different continental drift topic and plate tectonics topic. Students who receive prep A will read about continental shapes and age of the ocean floor, students with prep B will read about fossil distribution and marine sediment thickness, and students with prep C will read about till distribution and ocean physiography. All students will read about the basic idea of continental drift in preparation for class.

During the next class meeting, students will divide into teams, each with one A, one B, and one C representative. Each student receives a handout, a map illustrating locations of mid-ocean ridges, and a map illustrating locations of deep-sea trenches. In teams, students first discuss the lines of evidence for continental drift. Then, they look at their ocean floor data and the ridge and trench maps to look for patterns among the maps. Finally, they come up with hypotheses for why the patterns exist. This activity sets the stage for subsequent discussions about plate tectonics, as well as the difference between continental drift and plate tectonics. I have included some example maps, but you may already have your own maps of oceanic crust ages, marine sediment thicknesses, and ocean physiography that would be equally suitable for this exercise.

• student handout and color maps for "evaluating the lines of evidence for plate tectonics" assignment (Acrobat (PDF) 1.3MB May14 12)
• preparation exercises for continental drift and plate tectonics activity (Microsoft Word 2007 (.docx) 103kB May14 12)

On the day that the preparation exercises are distributed, it is important to let students know that (a) they will not be making formal presentations in front of the class; (b) there are three different prep exercises being distributed, so each person should use his/her own handout for preparation purposes. In the past, I have had students use a classmate's prep exercise instead of their own and had too many students do, for example, "A" preparations than "C" preparations. One obvious pitfall of this assignment is that some students will invariably be unprepared or absent on the day that the exercise is implemented. It will likely be the case that groups with multiple "A" representatives, a group missing a "B" representative, etc. will form. In the former case, I suggest that one of the "A" representatives share his/her continental drift information and the other "A" representative share his/her ocean floor data information. In the latter case, I have had "consultants" from other groups join groups with missing data. Finally, I have found that providing some discussion questions for students (I included some examples in the handout) breaks the ice and initiates the group work more efficiently than simply saying to students, "Explain your data to your teammates."