Teaching and Assessing Temporal Concepts

Rebecca Teed, Department of Earth and Environmental Sciences, Wright State University

I've recently taught geologic time and Earth history at three different levels, all for pre-service or in-service teachers. The biggest challenge has been the compressed (ten-week) introductory course required for pre-service teachers (preparing for pre-K-9th grade). I've taught this course fifteen times over the last eight years, using many of the same activities. I've started checking in the last year and learned that only about half of the students know how many thousands are in a million when they enter the course. According to Bill Slattery's research, they also struggle with proportional reasoning. Many of them are not interested in science, although the standards require most of them to teach it. When I developed my version of this course with Carrie Wright, she piloted activities that directly addressed geologic time and the skills that students need to understand it, and I still use versions of several of those activities.

For example, as homework, students draw personal timelines to linear scale on one side of a worksheet with 10-12 of the most memorable events of their lives. Our students are usually about 20-22, and their events are usually clustered in their most recent years. On the other side, they draw an Earth-history timeline, also linearly scaled, starting 4.5 billion, but mostly featuring Phanerozoic events. They also have to explain why the events on their timelines end up clustered close to the present. This engages student interest and gives them an opportunity to apply their proportional reasoning skills.

At the start and the end of this introductory course, the students take a 15-question multiple-choice test. This test was built using the Geoscience Concept Inventory (Libarkin and Anderson, 2005). I've analyzed responses to individual questions that deal with geologic and Earth history (Teed and Slattery, 2011). Most of the students enter the class with misconceptions, and it is hard to completely replace those in a single class.

Most of them think that the Earth somehow originated with Pangea on its surface both at the start and end of the course. However, most of them understand Pangea took millions of years to break up, and the others come to this understanding. Students really struggle with how we know the age of the Earth, initially assuming that our information is based on radiocarbon, fossils, and rock layers. They usually don't eliminate any of these, but will add uranium/lead dating on the post-test. The students were more likely to choose a correctly ordered timeline drawn to the correct scale on the post-test than on the pre-test. What was interesting was that students were more likely to choose a correctly scaled one at the end if they chose a correctly ordered one at beginning.

I am wondering if there are threshold concepts for geologic time, ideas that, once learned, make it easier to understand others (Meyer and Land, 2003). For example, students appear to have trouble understanding the scale of the geologic timeline under they are sure of the order of key events. Do they actually need to populate their timeline with events before they can work out that order? Likewise, do students need to understand the basics of uranium-series data before they will relinquish the misconception that scientists have determined the age of the Earth using more familiar (but irrelevant) dating techniques?

I got a new view of some of my old activities when I taught more advanced students at a summer workshop on climate change over geologic time (in-service science teachers grades 1-12). These students were willing to do more creative projects. For example, they studied climate mechanisms such as convection cells and the Coriolis effect for a week. Then, they were told that their colleagues in the life-science workshop next door were planning to travel back 230 million years ago to collect organisms and study evolutionary patterns. So the Earth-science students were given a map of Pangea and asked to apply their knowledge of climate mechanisms. They had to decide whether the place that their group had been assigned would be a good choice a base for time traveling researchers, in light of possible geologic and climate hazards. Several of them went beyond the assignment. One group partially designed their base, and another evaluated the risks in light of likely biodiversity patterns. I had tried this project with introductory students with little success.

Libarkin, J.C., and Anderson, S.W. 2005. Assessment of learning in entry-level geoscience courses: Results from the Geoscience Concept Inventory: Journal of Geoscience Education, v. 53, no. 4, p. 394–401.

Meyer, E., and Land, R., 2003, Threshold concepts and troublesome knowledge: linkages to ways of thinking and practising within the disciplines: ETL Occasional Report 4, http://www.tla.ed.ac.uk/etl/docs/ETLreport4.pdf (accessed 3 February 2012).

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