Radiometric Dating Isochron exercise

John Weber
Grand Valley State University - Geology
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This page first made public: Feb 10, 2012


Hands-on introduction to using the isochron method to determine radiometric ages.

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I use this as a homework problem, followed by a similar exam question, in our "Earth History" course.

Skills and concepts that students must have mastered

Students must have been introduced to isochron diagrams & understand how they work. Students must have been introduced to and have access to the basic and specific (Rb-Sr) radiometric decay equations and see how these relate to an isochron diagram - e.g., see Dalrymple (1991), Age of the Earth.

How the activity is situated in the course

This activity is used as a homework problem, followed by a similar exam question, in which a similar data set is plotted & students interpret and analyze the result.


Content/concepts goals for this activity

To be able to USE isochron diagrams.

Higher order thinking skills goals for this activity

Isochron diagrams allow one to address some important general questions related to radiometric dating: was there any initial daughter?, what was the original 87Sr/86Sr ratio?, was the system open or closed? In addition, they provide a visual way to understand the math (e.g. Dalrymple eqn 3.15) used to calculate the radiometric age of a sample.

Other skills goals for this activity

Using MS Xcl to plot & analyze data.

Description of the activity/assignment

This exercise introduces students to the use of isochron diagrams & the math behind them, by using, plotting, and analyzing a real data set.

Determining whether students have met the goals

Students turn in a graph and answers to a few questions that can easily be graded.

More information about assessment tools and techniques.

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Other Materials

Supporting references/URLs

  • Powell. J.L., (2001), Mysteries of Terra Firma.
  • Dalrymple, B., (1991), The Age of the Earth.