Answer:
C, E, H, A, B, F, K, D, L, G, J, I.
Explanation:
Hello,
In this case we are dating each layer based on its deepness as the deeper the layer is, the farther back in time it is (older). In such a way, the youngest layer is C and henceforth by going down, we find older and older layers no matter if the layer is horizontal or diagonal, we just go down by straight line, therefore, from youngest to oldest, the order turn out into:
C, E, H, A, B, F, K, D, L, G, J, I.
Best regards.