The mass ratios of 40Ar to 40K can also be used to date
Chapter 20, Problem 20.36(choose chapter or problem)
The mass ratios of 40Ar to 40K can also be used to date geological materials. Potassium-40 decays by two processes: 4 1 0 9K 1 21 0 e 88n 4 1 0 8Ar (10.7%) t1/2 5 1.27 3 109 yr 4 1 0 9K 88n 4 2 0 0Ca 1 21 0 e (89.3%) a. Why are 40Ar/40K ratios rather than 40Ca/40K ratios used to date materials? b. What assumptions must be made in using this technique? c. A sedimentary rock has a 40Ar/40K ratio of 0.95. Calculate the age of the rock. d. How will the measured age of a rock compare with the actual age if some 40Ar has escaped from the sample?
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