radioactive isotopes can be used to find age of rocks, fossils, or other artifacts. carbon-14 has a half-life of 5,730 years. suppose a sample of charcoal from primitive fire pit contains one eight of its original amount of carbon-14. how old is the sample?

a. 716 years
b. 17,190 years
c. 22,920 years
d. 45,840 years

Question

radioactive isotopes can be used to find age of rocks, fossils, or other artifacts. carbon-14 has a half-life of 5,730 years. suppose a sample of charcoal from primitive fire pit contains one eight of its original amount of carbon-14.  how old is the sample?

a. 716 years
b. 17,190 years
c. 22,920 years
d. 45,840 years

anonymous · Answer

A half life means that the isotope decays to half its original value in 5730 years. So in 5730 years it would have one-half the original amount. In another 5730, it would have 1/4 the original amount and in another 5730 years it will have 1/8 the original amount.I think b.

unklerhaukus · Answer

The amount of C-14 left in the sample is 1 eighth 
1/8 = (1/2)^3
so that is three half lives,
1 half life is 5730yrs , three half lives are 17190yrs