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 isotope is 50 million years,how old is the rock?
A)200 million years
B)400 million years
C)750 million years
D)1 billion years

Question

Quizplus · Accepted Answer

The ratio of 1:15 indicates four half-lives have passed (since 1/(2^4) = 1/16, close to 1:15). Four half-lives of 50 million years each equals 200 million years.

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