Ageologist is studying rock layers in a river delta. the layers are buried at a shallow depth beneath sediment that the river is depositing today. just like the sediment on top, the sediment in the rock layers was deposited by the river.

how might the geologist estimate how long it took to deposit the sediment seen in the rock layers?
a. use the layers' thickness and the current rate of deposition to calculate the time.

b. time how long it takes to dig a trench as deep as the rock layers.

c. construct a box as tall as the rock layers, and time how long it takes to fill it with a shovel.

d. the only way to estimate the time needed would be to sit for a few hours and watch new layers form.