Question

Upon examining layer M, you find that it contains a small proportion of the radioactive isotope - Potassium-40, which decays into Argon-40 with a half-life of 1.3 billion years. Assuming no contamination, what would be the age of a this layer if it contained 25% of Potassium-40 and 75% Argon-40?

Answer 1

Answer:

t = 2.6 billion years

Explanation:

If potassium becomes 25% of its initial value

so we can say it becomes half two times

as we know that 25% means it is 1/4 times of initial value

so we will have

$N = N_o e^{-\lambda t}$

here we know that

$N = 0.25 N_o$

$0.25 = e^{-\lmabda t}$

$ln 4 = (\frac{ln 2}{T_{1/2}}) t$

$t = 2 T_{1/2}$

$t = 2(1.3 billion \: years)$

t = 2.6 billion years