The mass ratios of ⁴⁰Ar to ⁴⁰K also can be used to date geologic materials. Potassium-40 decays by two processes:
a. ₁₉⁴⁰K + ₋₁⁰e ----> ᵢ₈⁴⁰Ar (10.7%)
b. ₁₉⁴⁰K ----> ₂₀⁴⁰Ca + ₋₁⁰e (89.3%)
c. t₁/₂ = 1.27 x 10⁹ years

1. A sedimentary rock has an Ar ⁴⁰K ratio of 0.95. Calculate the age of the rock.