Brett Samantha Dooley

Arts, Science, and Business Technology/ Patrick Henry Community College

Historical geology at Patrick Henry Community College is an introductory course for non-major undergraduates and has no college level prerequisites. Developmental reading and writing are the only prerequisites for the course.

Students should have an emerging sense of identifying invertebrate fossils to the phylum level and should be able to read a metric ruler before beginning the activity, for the time component of the activity. Since this is also an opportunity for synthesis from the course to date, students should understand the concepts of convergent and divergent evolution, sedimentary structures, and plate tectonics.

This is the culminating activity for the first part of the course, and an introduction to the remainder of it. The activity takes place at the beginning of the part of the course on Earth history. This comes after we have done a lab on basic fossil identification and discussed both techniques for dating rocks and geologic time in class. It is a stand-alone activity, but is referred to during the subsequent lessons.

The goal of this assignment is to give students a framework into which they can fit the material that will come in the course and provide a context for what is meant by deep time. While they studied the techniques for radiometric dating, it is not something they really "get." By seeing a scale distance of what this time involves the hopefully the exercise will make this more real for the students.

The full exercise in the museum is a synthesis of all that has gone into the course (minerals, rock types and structures, tectonic processes, evolution, radiometric and relative dating) prior to the specifics of what is revealed about geological and biological changes through time. While the time scale model itself does not bring in higher order skills, it provides a way for students to begin to get a feel for when these different events transpired or organisms lived in a greater context. A couple of examples of what they are doing in the lab beyond plotting on the timeline features from museum exhibits, include: 1) in one exhibit there is a model of a short stratigraphic column, and at the top are cross-bedded deposits. The students are to recognize these deposits for what they are and tell what it reveals about current direction, and 2) finding examples among the fossils on display of convergent and divergent evolution (they are given help with this).

Students work in collaborative groups to get this assignment finished. In different classes I have used different models. One I like is to have each group go through the exhibits to answer questions knowing that when we get back to class I will randomly select different groups, and individuals within each group, to explain the answers to questions for a section. In this way they are focused on making sure everyone understands what they are seeing. Each student also summarizes the field trip in a brief essay, working on both their writing skills and also processing the geology concepts.

This field trip provides a more visual introduction to the concept of deep time. The trip allows students to use exhibits in the state natural history museum as a way to synthesize the material from the previous five weeks of the course before the gears are changed to focusing on Earth changes through time. It also establishes a visual model for the depth of time and allows students to think about the museum exhibit (and what they reveal about the Earth) in a context of change over time. With the framework established in this field trip, they should be able to more meaningfully process the material that they learn in the coming weeks.

The focus of the museum as they designed the exhibits for this new building (which opened 4 years ago) was to show how a scientist can reconstruct the past based on modern observations, so my students are able to both begin to think about deep time by plotting the times for each exhibit on the time-line, and also begin to understand how the conclusions about the Earth's past were drawn.

Students are initially evaluated based on the collaborative effort of completing a worksheet as they go through the exhibits. They are individually evaluated based on the essay they write explaining their experience, and also evaluated with questions on the exam.

Morris, P. (2000) Comprehending Geologic Time. Athro-Limited. Retrieved January 27, 2012 from http://www.athro.com/geo/hgfr1.html.

Wenner, Jennifer (2011) Toilet Paper Analogy for Geologic Time. Teaching Quantitative Skills in the Geosciences. Retrieved February 7, 2012 from http://serc.carleton.edu/quantskills/activities/TPGeoTime.html.