A fossilized leaf contains 15% of its normal amount of carbon 14. How old is the fossil (to the nearest year) ? Use 5600 years as the half-life of carbon 14.

To determine the amount of substance left (At) in t years we use,

At = (Ao) x e^-kt

where Ao is the initial amount and k is the constant. Substituting the given half-life

At / Ao = 0.5 = e^-k (5600)

The value of k is 1.2377x10^-4

Using the same equation,

At / Ao = 0.15 = e^ - (1.2377x10^-4) (t)

The value of t is 15327. Thus, the fossil is approximately 15327 years old.