Radiometric Dating Isochron exercise
Grand Valley State University - GeologyAuthor Profile
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Hands-on introduction to using the isochron method to determine radiometric ages.
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.
Teaching materials and tips
- Rb-Sr isochron problem (Microsoft Word 555kB Feb8 12)
- Rb-Sr Isochron plot solution (Excel 18kB Feb8 12)
- Weber, B. and Kohler, H. (1999) Sm–Nd, Rb–Sr and U–Pb geochronology of a Grenville Terrane in Southern Mexico: origin and geologic history of the Guichicovi Complex. Precambrian Research, v. 96, n. 3-4, p. 245-262.
- Powell. J.L., (2001), Mysteries of Terra Firma.
- Dalrymple, B., (1991), The Age of the Earth.