A datable mineral crystal contains 40% parent isotope. How many half-lives have passed since the crystal formed?
A)1
B)more than 1 but less than 2
C)more than 2 but less than 3
D)more than 3

Question

Quizplus · Accepted Answer

If a mineral crystal contains 40% parent isotope, it means that 60% of the original parent isotope has decayed. After one half-life, 50% of the parent isotope would remain. Since 40% is less than 50%, more than one half-life has passed, but since it's still a significant amount, it's less than two half-lives.

A Datable Mineral Crystal Contains 40% Parent Isotope