Chapter 29, Problem 4RQ

In a sequence of sedimentary rock layers, the oldest layer is on the bottom and the youngest layer is at the top. What relative dating principle is this?

To determine

The relative dating principle used in a sequence of sedimentary rock layers, the oldest layer is on the bottom and the youngest layer is at the top.

Answer to Problem 4RQ

Original horizontality, also known as the principle of superposition, states that older layers of sedimentary rock got deposited first. Then all the layers got deposited one after another over the initially formed layer. Hence, lower layers of sedimentary rocks are older than the upper layers.

Explanation of Solution

Sedimentary rocks are formed by the deposition of different layers of sediments one over another. This is an along process. The upper layer has been deposited over the lower (older) layer.

So, it can be said that the upper layer is relatively younger than the lower. This can be understood by the principle of original horizontality or the principle of superposition.

According to the principle of Original horizontality, sediments get deposited on the horizontal surfaces. On this layer, other layers got deposited one after another. Therefore, the layer which is in the bottom is older than that of the layer, which is on the top.

Conclusion:

Thus, Original horizontality, also known as the principle of superposition, states that older layers of sedimentary rock got deposited first. Then all the layers got deposited one after another over the initially formed layer. Hence, lower layers of sedimentary rocks are older than the upper layers.