Suppose the ratio of radiogenic ⁴⁰K to nonradiogenic ³⁹K was 1:10 at the time a rock was formed, and that at that time also the ratio between radiogenic ⁴⁰Ar to ³⁹K was 1:20. Now, when the rock is analyzed, it is found that the ratios are ⁴⁰K/³⁹K = 1:20 and ⁴⁰Ar/³⁹K = 1:10. How old is the rock (in billions of years)?

Question

Quizplus · Accepted Answer

The decay of radiogenic 40K to 40Ar over time changes the ratios. The initial and current ratios can be used to calculate the age of the rock using the known half-life of 40K, which is approximately 1.25 billion years. The change in ratios indicates that one half-life has passed, making the rock approximately 1.3 billion years old.

Suppose the Ratio of Radiogenic 40K to Nonradiogenic 39K Was

Suppose the Ratio of Radiogenic ⁴⁰K to Nonradiogenic ³⁹K Was