John Weber
,
Grand Valley State University - Geology
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#### Summary

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

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## Context

#### Audience

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.

## Goals

#### 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. 