Teaching about Time

Maria Waller, Geosciences Department, Wellesley College

I teach introductory geology labs at Wellesley College and work closely with my colleague Kathleen Gilbert who is also attending this workshop. When we teach about time in our labs, it is primarily in the context of earth history, sequencing geologic events and processes through time. When I began teaching, I expected that the vast scale of geologic time would be difficult for students to grasp. It is hard to conceive of spans of time so much greater than our own experience. Over the years, however, I have found that students struggle more with unraveling sequences of geologic processes that are embedded in the rock record. It is hard to think of one concrete object, like a rock, as representing a span of time. While most of our students can understand that geologic processes act on earth materials at different rates and in different places, they find it much more difficult to reconstruct a history of these processes from the existing, observable geology.

When I help students with this, I try to make the problem as visual as possible and break the problem into pieces. For example, if a student can understand that part of history is changing environments through time, then she can consider each environment individually, compare it to her knowledge of modern environments and think about the processes that might change one environment to another. I try to emphasize cause and effect when students consider change through time. This is something that students often seem to lose sight of or confuse.

In our labs we spend a lot of time teaching students about earth materials like minerals, rocks and sediments and the processes by which they form. This leads to thinking about earth history and time as an application of what they've learned. We try to help them visualize as many components of this as possible by modeling some processes (e.g. using stream tables) and going into the field to see these things for themselves and develop an appreciation for the physical scale of geology. I think that students' understanding of physical scale affects their understanding of time when thinking about geologic history.

Though we emphasize understanding geologic processes in our labs, we don't have any lab exercises that address the rates at which various geologic processes progress. This is something that some of the more curious students do ask about. I would be very interested to hear thoughts about ways to incorporate this into our curriculum.

As I read through the materials and posts for this workshop, I am very interested to see how many different facets there are to the study of time, many that I have never thought about. I look forward to exchanging ideas, learning a lot and being able to bring back new ideas for our course.

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