Karen Viskupic

Department of Geosciences, Boise State University

The activity is designed for 8th/9th grade Earth Science students, but I have also used it with 5th grade students. It could easily be modified for use in 100-level geoscience courses.

Students should be able to read x-y plots and divide two numbers.
Students should be familiar with relative dating principles, although instruction on these principles could be added to the beginning of the activity.

It can be used as a stand-along exercise or as part of a sequence of exercises relating to geologic time.

Students compare relative and numerical dating techniques
students are introduced to radioactive decay, half-lives, and U-Pb geochronology

Students must evaluate whether or not their relative and numerical ages are consistent with each other.

graph reading

Students review relative dating principles by interpreting a block diagram and are then introduced to radioactive decay and the concept of half-life to determine numerical ages. There is some ambiguity in the block diagram, so students must determine numerical ages for samples from the block diagram to test their relative age hypotheses. Students "date" samples from the block diagram by counting the number of 235U and 207Pb atoms (colored beads) in a zircon (Ziploc bag).

Students should come up with the intended ages for their zircons and should be able to evaluate whether or not their relative age hypotheses are consistent with the numerical dates. This is evaluated through group discussion.