The oldest layer in the diagram is

In the diagram, layer 1 has rocks which are the oldest. Explanation. Rocks are arranged in layers that contain fossil with the oldest fossils represent at the deepest layers and the youngest fossils present near the top. Using this concept, the oldest rock layers are located at the bottom (layer1) and the youngest at the top(layer 6).

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.