Question

4. (20 pts) Potassium-Argon dating is used in geology and archeology to date sedimentary rocks. Potassium 40 decays by two different paths: 10K → 20Ca + _e (89.3%) 10K → 18 Ar+je (10.7%) The overall half-life of for the decay of potassium-40 is 1.3 x 100 years. Estimate the age of sedimentary rocks with an Argon 40 to Potassium 40 ratio of 0.0102.

Answer 1

Amswer (89.3) Ca t -1 19 2o Clo.?) 19 ovivoll hall- lile k-4o 1.3 x l0 Years For k-40 to Ar-40 dulay is lo.% Hal lile lor K-40 to Ar-40 is = o.lo?x1-3x lo 391Xlo Years Nos Delay lovmula N/E) No edt o.693 Half lie lormula : t 0.693 1391x108 = 4.982 x lo 9

Av-40 to k-40 Yatio - o olo2 ie Nlt) -0.olo2 t (4.982 x lo) e ..o.olo2 = lolo.0l01) 4.982x 161t t- 9.2x 10 Years 9.2 x 10 Years Age d Yocks with Ar-4o to k-4o is 92 billion Yeavs 1