Hello. You forgot to add the diagram to your question. The diagram is attached below.
Answer:
The oldest rock layer is represented by the letter F.
Explanation:
Rocks are mainly responsible for the formation of soils. This occurs through weathering, which sediments the rock into small particles that form the soil above that rock. When weathering is affecting the rock it has several layers in different weathering states.
In this way we can see that as weathering acts on the layers of sediment, the original rock is the deepest layer and therefore the oldest. Accordingly, we can say that in the diagram below the oldest rock layer is the one represented by the letter F.
According to the all-or-none law, it a certain threshol is crossed by a stimulus' strenght, it will cause a response in the nerve cell or muscle fiber. However, the strenght of the response will always be the same and will not vary with different stimulus strengths. The only requirement is for the threshold to be crossed.