Question

part 1 absolute dating

1. how many years does it take for

half of the material shown in the
graph to go away?

1. after 3 half lives, how much of the

original material is still left?

1. how many years have gone by

after 3 half lives?

1. after 0 half lives, how much of the

original material is still left?

1. after 75 years, how many half

lives have gone by?

1 half life is 15 years
percentage
of material
remaining

Explanation:

Question 1

Step1: Recall half - life definition

Half - life is the time it takes for half of a radioactive (or decaying) material to decay. From the graph's note, 1 half - life is 15 years. And by the definition of half - life, the time for half the material to go away is the half - life.

Step1: Recall the pattern of half - life decay

After 1 half - life, 50% (or $\frac{1}{2}$) of the original material remains. After 2 half - lives, the remaining material is $50\%\times50\% = 25\%$ (or $\frac{1}{2}\times\frac{1}{2}=\frac{1}{4}$) of the original. After 3 half - lives, the remaining material is $25\%\times50\%=12.5\%$ (or $\frac{1}{4}\times\frac{1}{2}=\frac{1}{8}$) of the original.

After 0 half - lives, no decay has occurred. So the amount of the original material left is 100% (because we start with the full amount of the original material before any half - lives have passed).

Answer:

15 years

Question 2