Potassium-40 decays to argon-40 with a half-life of 1.27 x 10^9 years. What is the age of a rock where the number ratio of potassium-40/argon-40 is 1.72?

Question

Potassium-40 decays to argon-40 with a half-life of 1.27 x 10⁹ years. The resulting argon remains trapped in the rock for most minerals. What is the age of a rock where the number ratio of potassium-40/argon-40 is 1.72?

Answer 1

Step 1: calculate the % Ar-40

Step 2: calculate the number of half-life passes to make the ratio

Step 3: calculate the ago of the rock

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