In an unweathered sample of igneous rock,the ratio of an unstable isotope to its stable daughter isotope is 1/15.If no daughters were present at the time the rock cooled below closure temperature,and the half-life of the reaction is 50 million years,how old is the rock?
A)200 million years
B)400 million years
C)750 million years
D)None of the above are correct.

Question

Quizplus · Accepted Answer

The ratio of 1/15 indicates that four half-lives have passed (since 1/15 is approximately 1/16, which is 2^4). Therefore, the age of the rock is 4 half-lives, or 4 x 50 million years = 200 million years.

In an Unweathered Sample of Igneous Rock,the Ratio of an Unstable