A rock sample contains 1/8 micrograms of the parent radioactive isotope Al-26 and 7/8 micrograms of its daughter isotope Mg-40. If the half-life of this decay is approximately 700,000 years, how old is this rock?

Question

Quizplus · Accepted Answer

The rock has gone through three half-lives to have 1/8 of the parent isotope remaining (1/2 to 1/4 to 1/8), so the age is 3 half-lives x 700,000 years = 2.1 million years.

A Rock Sample Contains 1/8 Micrograms of the Parent Radioactive