Exercise: K-Ar age calculation

Use the information provided in the overheads, and the following data to calculate the age and initial Ar-isotope composition of five rock fragments (1-5) that have been separated from a single lava flow and analysed by mass spectrometry.

Isotope composition of the five rock fragments:


How you should do it: First, plot the datapoints in an isochron diagram, using a spreadsheet. Then calculate the slope and y-axis intercept (if you use Excel, there are the functions slope() and intercept(), or steigung() and achsenabschnitt() if you use a german version). Then use the equation in the overhead that defines the slope and reorganize it so that you can calculate t (note that ln e^x = x, further be careful with the units, as the decay constants are provided in 1/a where a means year). The decay constants are given in overhead 4.

Provide your answer as a PDF if solved using Excel, or as a scan if solved by hand. Not only provide the result, but also the way you did the calculation!

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Please note: If not stated otherwise, the exercises have to be solved before the next lecture starts, and need to be uploaded in time in OPAL, preferrably as a PDF document. Submitting spreadsheet files is permitted.

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