"ZirChron" Virtual Zircon Analysis App
We will demonstrate the first element of the student exercise available here. Participants in the teaching demonstration will use the Zir-chron app on their laptop or tablet to explore the functionality of the app and engage in the geochronological experimentation it allows, in order to understand how the curriculum scaffolds student learning.
This application was developed to promote deeper understanding of the science of geochronology, including the integration of crystal-scale relative dating principles with numerical dating via radioisotope measurements. An integral aspect of developing this understanding is practical experience with the decision-making that goes into the selection of samples for analysis, and the subsequent interpretation of the resulting isotopic ages from those samples. The U-Pb decay system in zircon is particularly amenable to this practice, as we can apply different methods—in situ laser ablation inductively coupled plasma mass spectrometry and high-precision chemical abrasion isotope dilution thermal ionization mass spectrometry—to the same crystals, and link the resulting radioisotopic ages to the textures within crystals revealed by cathodoluminescence imaging.
By the end of this activity, students will be able to:
- Apply relative dating principles at the crystal scale
- Describe the statistical distribution of the crystal ages including means, modes and outliers
- Form hypotheses relating the statistical distribution of crystal ages to the physical characteristics of those crystals
- Form and test hypotheses about the geologic processes that could account for the distribution of crystal ages in a population
- Describe the decisions made to determine the geologic age of a rock from a set of crystals
This activity is designed to be flexible in its deployment, with content and activities that engage students from high school to graduate levels. I have used this activity in three courses: a lower-division undergraduate required course in field methods; an upper-division undergraduate required course in geochemistry; a graduate course in isotope geochemistry.
Why It Works
The activity is centered around hypothesis formation and experimentation. Students interact with the learning environment by using visual criteria to select zircon crystals or spots on crystals for analysis, evaluating the numerical and graphical results, and then using those results to revise their analyses and interpretations.
Students are assessed on the basis of their responses to a set of questions formulated as a student exercise, with particular emphasis on a set of wrap-up questions that prompt students to synthesize and reflect on their learning.