Chapter 14, Problem 8A

Summary Introduction

Introduction:

A fossil is any preserved evidence of an organism. Radiometric dating is used to measure the age of rock. It uses decay of radioactive isotopes to measure the age of rock. The method requires that the half- life of the isotope is known. The relative amounts of radioactive isotope and its decay product must also be known.

Answer to Problem 8A

Correct answer:

The correct answer is option D. 125 years

Explanation of Solution

Explanation/justification for the correct answer:

Option D. 125 years−Assuming that one can date a material only if it has one percent of radioisotope remaining, it would not be possible to date the given material after 125 years. According to the graph, there is hardly any radioisotope left after 108 years.Hence this is the correct option.

Explanation for incorrect answer:

Option A. 35 years−As per the graph, there is more than 20 percent of radioisotope left after 35 years. So it is possible to date the material after 35 years. Hence, this is not the correct option.

Option B. 50 years- As per the graph, there is more than 10 percent of radioisotope left after 50 years. So it is possible to date the material after 50 years. Hence, this is not the correct option.

Option C. 75 years−As per the graph, there is more than 5 percent of radioisotope left after 75 years. So it is possible to date the material after 75 years. Hence, this is not the correct option.