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Teaching about Geochronology: Absolute (Numerical) Ages

This web page is based on a document produced by Erica Crespi, Maya Elrick, Jessica Kapp, Margaret Mayer, Mark Schmitz, Roger Steinberg, Gina Szablewski, John Weber, and Susan Zimmerman at the 2012 workshop on Teaching About Time.

Introduction

Geochronology - the process of determining numerical ages and dates for Earth materials and events - is fundamental to understanding geologic time and geologic history. Although this topic is essential to understanding and appreciating geoscience, it is routinely overlooked and superficially addressed in introductory textbooks, many of which omit the mathematical aspects of radiometric dating (Shea, 2001). In addition, many students arrive in college classrooms with misconceptions about basic chemistry that interfere with their ability to understand radioactive decay and its use in geochronology (Prather, 2005).

Recommendations for Teaching

Based on our collective experiences as geoscience educators and/or geochronologists, here are our recommendations for teaching about this essential topic in geoscience.

Articulate learning goals (to yourself and to your students)

The first step in teaching effectively about any topic is determining what your learning goals are for your students. What is it that you want your students to know, understand, and to be able to do, related to geochronology? Here are a few examples of learning goals related to geochronology; you may wish to revise, select from, or expand on these for your own classes.

A student that has successfully learned about geochronology will be able to:

Review basic chemistry to address student misconceptions

Use analogies, particularly for things we cannot observe directly

Use "scaffolding": build from simpler, familiar ideas to more complex, less familiar ones

When people learn, we build on what we already know. As teachers, we can enhance this process by explicitly linking new ideas to familiar concepts. For example:

Have students solve real problems using real data

Having students solve real geologic problems gives them the authentic experience of doing science. Here are a couple of examples of teaching activities that use real data to teach students about radiometric dating:

Review the process of science as you address students' questions

Thoughtful students are likely to ask thought-provoking questions about geochronology, such as

Answering these questions is critically important. If we ignore them, we run the risk of reinforcing students' misconceptions that radiometric dates are unreliable. Acknowledging the challenges of radiometric dating, while explaining how scientists know what we know, deepens our students' understanding both of geochronology and of science. Mark Schmitz and Karen Viskupic at Boise State University have put together several slide sets that explain and show, in detail, how U-Pb geochronology is done.

References

Prather, Edward (2005), Students' Beliefs About the Role of Atoms in Radioactive Decay and Half-life. Journal of Geoscience Education, v. 53, n. 4, pp. 345-354.

Shea, James (2001), Teaching the Mathematics of Radiometric Dating. Journal of Geoscience Education, v. 49, n. 1, pp. 22-24.


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