Chapter 27, Problem 10TE

To determine

The reason behind the fact that the most ancient rocks are found on the continents rather than on the ocean floor.

Answer to Problem 10TE

The reason behind the fact that the most ancient rocks are found on the continents rather than on the ocean floor is subduction.

Explanation of Solution

The ocean floor is constantly created and destroyed rather quickly. The new ocean floor is created in the mid-ocean ridges from hot magma rising in the mantle, coming out of the ridges, and then spreading away.

As the ocean floor plates move towards the continents, it is recycled into the mantle, as it is drawn downward into subduction zone. The continental crust is less dense, so the oceanic crust subducts back to the mantle. This process explains why the younger rocks are found on the ocean floor.

Conclusion:

Therefore, the reason behind the fact that the most ancient rocks are found on the continents rather than on the ocean floor is subduction.