Teaching Time Both Traditionally and Unconformably

Gina S. Szablewski, Geosciences Department, Univeristy of Wisconsin - Milwaukee

As a lecturer of large enrollment, introductory geology classes, I have taught the subject of geologic time in every semester for over 10 years. While the depth of the material I cover does vary by the class, the approach basically is the same. My physical geology and earth science classes cover the subject over an entire chapter, which is completed in about a week of time during the middle of the semester, while my environmental geology class covers the topic very briefly as part of an introductory chapter at the beginning of the semester. Currently, this environmental geology class is completely online. The following primarily concerns my in-person lecture classes.

I do not consider my overall teaching style as traditional. However, I do think my approach to teaching about time is fairly traditional, and when I think about it, it does not seem like I am doing anything new or innovative with this subject. I cover the development of the time scale, discuss relative and numeric principles, use the calendar year as a metaphor for geologic time, and use the Grand Canyon as an example. I do set the memorization of the primary facts of the geologic time scale as one of my learning objectives for this subject. I do not usually ask my students to memorize items outright, but in this case, I think it is an important frame of reference akin to knowing the names of oceans and continents.

One of the exercises I complete with my students is the creation of concept sketches (Johnson and Reynolds, 2005). I think it is integral that my students take the information I am sharing with them and make it their own, and they need to do this with a solid foundation to avoid misconceptions. Drawing geologic processes and ideas provides my students with a secondary, and perhaps deeper, type of learning.

After I have discussed a subject, and in this case it is unconformities, we draw the development of each unconformity as a series of four simple steps. I do the work on the Smartboard while they each draw the sketches in their seat. I encourage quiet discussion of the drawings while the work is being done. Instead of just showing them photographs of unconformities and explaining how they formed, they can create their own unconformities and hopefully understand the process better. Overall, my students who do work on the concept sketches do very well with unconformities on the exam, and it is very easy to pick out who has not participated in class. I do think these sketches have been successful. I also use a child's photograph album analogy when I am discussing unconformities; aka, it is not that nothing happened during a certain time period, it is just that it is not recorded with a photograph (because your mom was too busy taking care of you and your siblings instead of taking pictures.) This analogy is easy to understand and it makes them laugh.

My intention has been to transition the concept sketch exercises from individual to small group work done on white boards. I think my students will learn more from each other's mistakes and misconceptions, and add a little more student input with a little less lecture. With only weak excuses, I have yet to take the leap of creating these groups in a class of 200 students.

I do think my students struggle with the how radioactive dating works and is applied to geologic time, but I have not come up with a favored approach for this topic. I can say the same for correlation of rock units. With these two topics, I have taken the approach of the textbooks I use because I do strongly believe in them. I would like to try something new for either of these topics.


Johnson, J. K., and Reynolds, S.J., 2005, Concept sketches – Using student- and instructor-generated annotated sketches for learning, teaching, and assessment in geology courses. Journal of Geoscience Education, v. 53, pp. 85-95.

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