Carbon- 14 dating is used to date a bone found at an archaeological excavation. If the ratio of $\mathrm{C}-14$ to $\mathrm{C}-12$ atoms is $3.25 \times 10^{-13}$, how old is the bone? [Hint: Note that this ratio is $\frac{1}{4}$ the ratio of $1.3 \times 10^{-12}$ that is found in a living sample.]