Building Isochrons and Determining the Ages of Three Rocks
Page 15 of 17
For each of the three rocks listed below follow these steps to determine the rock's age of formation.
1. Prepare an isochron by plotting the points that represent the amounts of isotopes Rb-87 and Sr-87. (The values are RATIOS of parent and daughter to the stable isotope, Sr-86. Mass spectrometers measure ratios and not absolute amounts.) Plotting Instructions
2. Click "Verify Points" and then use the "regressor" to find the slope and intercept of the line that Best Fits the points. The process, called "Least Squares," will result in the best value for the slope. Regressor Instructions
3. The age of the rock will be calculated for you. After you minimize the error term, click the "Verify Age" button, and if age is OK, transfer the rock's age to the table on the right. After completing table, click the "Next" button to receive your CERTIFICATE of completion as a Geochronologist.
   
Sample
Locality

Age (Million years)

Granite Scottish Highlands
Gabbro Sudburry, Canada
Gneiss Greenland

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