A swimmer enters a gloomier world (in one sense) on diving to greater depths. Given that the mean molar absorption coefficient of seawater in the visible region is $6.2 \times 10^{-3} \mathrm{dm}^3 \mathrm{~mol}^{-1} \mathrm{~cm}^{-1}$, calculate the depth at which a diver will experience half the surface intensity of light.
0.87