A micropaleontologist in Oslo analyzes sediment layers and finds that the ratio of oxygen-18 to oxygen-16 isotopes decreases exponentially with depth. At 10 meters depth, the ratio is $R = 0.002$, and at 30 meters, it is $R = 0.00032$. Assuming $R(d) = R_0 e^-kd$, find $k$ to four decimal places. - Abu Waleed Tea