Question

Birds today have bones with 10mg of Ca-50. A bird bone is found with only 1.25mg of Ca-50 in it. If the half-life of Ca-50 is 4 years, how old is the bone?

a) 16 years old
b) 12 years old
c) 8 years old
d) years old

Answer 1

Answer: answer is C

Explanation: got it right on my test

Answer 2

Using the concept of half-lives, we determine that the bone with 1.25mg of Ca-50, down from the original 10mg, is 12 years old, as it has gone through three half-lives.

Step-by-step explanation:

The bone is 12 years old. To determine the age of the bone, we apply the concept of half-lives. Starting with 10mg of Ca-50, one half-life (4 years) would leave 5mg. After two half-lives (8 years), we would have 2.5mg remaining. After three half-lives (12 years), there would be 1.25mg of Ca-50, which is the amount found in the bone. Hence, the bone has gone through three half-lives and is therefore 12 years old.