TEACHING TIME IN LARGE INTRO CLASSES: AN ACTIVE APPROACH

Teaching deep geologic time presents a number of challenges in large general education courses. First, our general education courses are very large, up to 300 students. Second, at Arizona these courses are for non-science majors only, with many students lacking basic mathematical skills such as scientific notation that can help establish the great length of geologic time. Third, for the vast majority of students in our classes, this is the first, and last, geology course they will take.

We have adopted several active approaches to address some of these challenges. In one, we use a 45 foot rope to represent the Earth's history. While this is probably very common, we try to involve the class actively. We use about 20 randomly selected volunteers from the class, each given a 3x5 card with an important geologic event written on it, and a clothes pin. The events are numbered from the beginning of Earth history ~4.6 billion years ago to the end of the last major glaciation event about 10,000 years ago. These 20 students, one by one, are asked to come to the Geologic Rope and place their card on the rope at the right point along the rope. This helps to show how bunched up major geologic events are in the relatively recent past, that dinosaurs are a relatively recent life form, etc. Most of this may be similar to many classrooms, but we have attempted to involve the entire class at the same time. Students, individually and as part of a graded quiz, have to calculate the percent of Earth's history either from the beginning or back from the present, of major geologic events, such as the beginning of well-preserved fossils or the extinction of the dinosaurs. And once they have the percentages, they must convert this into ages in their own lives, which they can approximate as 20 years for most. This last aspect is very important, for it emphasizes basic quantitative skills while at the same time helping students relate Earth history to the time line of their own lives. They are typically amazed when their calculations show that, on their individual timeline, dinosaurs went extinct just over three months ago.

I will also show other activities we use for radiometric age dating in these large classrooms, with an emphasis on addressing the common misconception that all radioactive material is gone after two half lives.