Discovering the Principles of Relative Age Determination – a Think-Pair-Share In-Class Activity
In this in-class activity, students are challenged to identify rock units and geologic features and determine the relative ages of these features without prior instruction in the classical methods of relative age determination. Field photographs and satellite images are the data from which students make their observations and interpretations. Students are introduced to the formal language of relative age interpretation after this experience with employing the concepts.
- gain experience with "field" observation and recognition of rock units and geologic features.
- apply logical reasoning to interpret sequences of events.
- derive principles of relative age determination.
- begin to develop a sense of "deep time" as they are challenged to imagine how long it would take to develop the sequences of events that they have interpreted.
Methods of GeoscienceField observation and principles of relative age determination such as Steno's Laws of Superposition, Original Horizontality and Original Lateral Continuity, and Hutton's principles of crosscutting relationships and included fragments are fundamental methods for geological investigation. Principles of relative age determination are commonly taught through description in lecture or with line diagrams (cross sections and block diagrams) in a "lab" or homework assignment. These verbal and diagrammatic presentations may seem abstract to students and they may have difficulty applying these principles in real world situations. This activity builds the fundamental skill of observation and gives students practice in determining relative age relationships in a classroom setting that more closely models field observation and discussion.
Context for Use
Description and Teaching Materials
With this foundation, the class is presented with a series of field photographs and satellite images in a PowerPoint presentation. Images include terrestrial outcrops and satellite images from Mars and Europa. For each image, students are instructed to make observations and interpret age relationships. In the whole class discussions that follow each image, students share their observations and interpretations and are asked to explain how they interpreted relative age relationships. Nine to ten images can be discussed in a 50-minute class. Remaining images are assigned as homework and discussed in the following class. It is only after these experiences that the instructor presents the formal language of relative age determination.