Question

40K decays to 40Ar with a half-life of 1.25 x 109yr. Assume that rocks contain no 40Ar when they form, and that the only way 40Ar can be present is through the decay of 40K. If the ratio of 40K to 40Ar in a particular rock is found to be 1:3, what is the age of the rock?
A) 1.25 x 109yr
B) 2.50 x 109yr
C) 3.75 x 109yr
D) 5.00 x 109yr
E) cannot be determined without knowing how much 40K was in the rock to begin with

Answer

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