Potassium-40 has a half-life of approximately 1.25 billion years. approximately how many years will pass before a sample of potassium-40 contains one-sixteenth the original amount of parent isotope?

In a first-order chemical reaction, the half-life of the reactant is computed by ln (2) / λ/. Where:λ is the reaction rate constant.

In terms of radioactive decay, the half-life is the extent of time after which there is a 50% probability that an atom will have completed a nuclear decay.

Since (1/2) ^4 = 1/16, that would require 4 half-lives, which is 5 billion years.