We can also use radioactive decay of 14C (radiocarbon) into 14N...

Question

We can also use radioactive decay of 14C (radiocarbon) into 14N (nitrogen) to date animal and plant remains. The half-life of 14C is approximately 5500 years. We measure the amount of 14C in a piece of mammoth bone to work out how old it is. We find that only 25% of the original 14C is left so how old is the mammoth bone?

A. 22000 years

B.16500 years

C.11000 years

D.1375 years

Answer 1

An easy formula to use is fraction remaining = 0.5^n where n = # of half lives elapsed.

In this problem, we have the fraction remaining (25%, or 0.25) and we can solve for n, the # of half lives.

0.25 = 0.5^n

log 0.25 = n log 0.5

-0.602 = -0.301 n

n = 2 half lives have elapsed.

To find the age, or number of years that corresponds to, ...

2 half lives x 5500 yrs/half life = 11,000 years

ANSWER = C