DELIVERY AND ASSESSMENT OF A HALF-DAY INTEGRATED FIELD AND LABORATORY EXPERIENCE FOR UNDERSTANDING GEOLOGIC TIME AND GEOCHRONOLOGY

This research was centered on a half-day field and laboratory experience for students in grades 5-12. Goals for the experience include increasing students’ understanding of using rocks as a record of Earth’s history, relative and absolute time, field observations, radioactive decay and geochronology, and the geologic time scale.

The first half of the experience exposed students to outcrops of western Snake River Plain rhyolite, basalt and sandstone within Boise city limits. As students engaged in a walking tour each outcrop was described, lithologically identified and mapped on a poster sized air photo. Key outcrops were used to practice relative dating principles including superposition, original horizontality, cross-cutting and host-inclusion relationships. The outcome of the exercise was a field map emphasizing basic geologic history. Students generated hypotheses about the relative age of the rock units, and we discussed how their hypotheses could be tested in a laboratory with absolute dating methods.

The second half of the experience, which took place at Boise State University, included three active learning activities: development of a personal life timeline, interpretation of relative age using a geologic block diagram, and exploration of simulated radioactive decay using bags of colored beads to represent parent, daughter and essential constituents in a mineral sample (www.earth-time.org). Samples represented by these “atoms” were linked to rock units in the block diagram to illustrate how absolute age constraints test and inform relative age hypotheses. Following these activities students were led on an interactive tour of Boise State’s U-Pb geochronology facility.

Student learning was pre- and post-assessed using a selected response instrument and a delayed test follow-up worksheet that asked students to draw and describe a picture of what they learned. Results from one 5th grade class (n=14) showed most students performed well on the pre-test and had gain in their understanding. Analysis of the reflective worksheet revealed deep understanding of the field trip activities. Drawings communicated geologic relationships observed in the field, mass spectrometers, and graphical representations of radioactive decay and half-lives.