Alg2
posted by Rock on .
An anthropologist finds there is so little remaining Carbon14 in a prehistoric bone that instruments cannot measure it. This means that there is less than 0.5% of the amount of Carbon14 the bones would have contained when the person was alive. How long ago did the person die? Round your answer to the nearest thousand. (22,000, etc)

Find the halflife of C14. Call it n years
2^(t/n) < .005
t/n < ln(.005)/ln(2) = 7.64
t > 7.64n
check: 2^7.64 = .005013, so after 7.64 halflives, we are down to .5% of the original.