## A Geochronology Puzzle – Integrating Relative and Absolute Age
Studies in Introductory Courses

Friehauf, Kurt C.^{1}, Dilliard, Kelly^{2}, and Pope,
Michael C.^{2},

^{1}Dept. of
Physical Sciences, Kutztown University, Kutztown, PA 19530,

^{2}Department
of Geology, Washington State University, Pullman, WA 99164-2812

We designed a geochronology puzzle homework to facilitate the
understanding of the differences between relative and absolute dating
and how the two methods combined can yield a more complete history of
geologic events. This homework assignment is a two-week exercise with
multiple steps that addresses several learning goals, including: 1)
using relative dating techniques to establish an order of events; 2)
creating data tables and graphs in Excel for generating an exponential
decay curve; 3) calculating radiometric ages using isotope
concentrations and the generated decay curve; 4) using radiometric
geochronology to help resolve ambiguities in the relative order of
events; and 5) writing up the results in a summary narrative.

Students first determine the relative ages of rocks and events from a
geologic cross section and turn in this list during the first week's
laboratory section. Students are then guided in making an exponential
curve for the U/Pb system using Excel as a homework assignment with
step-by-step instructions. Students first make a spreadsheet of
half-lives, number of years corresponding to each half-life, amount of
U and Pb, and the U/Pb ratio. From this spreadsheet, students make a
scatter plot of the number of years versus the U/Pb ratio. Students
then modify the graph, changing both the x and y scales and its overall
appearance. Using isotope data for igneous and metamorphic rocks
provided, students calculate the corresponding radiometric ages.
Finally, students compile their results and summarize the sequence of
geologic events in a typewritten narrative that explains their
reasoning.

This summary writing exercise reinforces the idea that geologic time
problems are not merely abstract puzzles, rather they correspond to
historical events. Students who did this exercise performed better on
these topics in both lab and lecture exams than previous students.

2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Session No. 60--Booth# 26

It's About Time: Teaching the Temporal Aspects of Geoscience (Posters)

Salt Palace Convention Center: Hall C

6:00 PM-8:00 PM, Sunday, 16 October 2005

Geological
Society
of America Abstracts with
Programs, Vol. 37, No. 7, p. 152.