Question

1. practice: theory of plate tectonics

self assessment

1. practice: theory of plate tectonics

respond to the following based on your reading.
question 1
why have rocks older than 200 million years never been found in the oceans? explain how the movement of tectonic plates is responsible for this recycling of the ocean floor.

Explanation:

The oceanic crust is constantly being recycled due to plate - tectonic activity. At mid - ocean ridges, new oceanic crust is formed as magma rises and solidifies. As the tectonic plates move apart at these ridges, the older oceanic crust is pushed away. At subduction zones, the denser oceanic crust is forced beneath the less dense continental crust or another oceanic plate. This subduction process causes the older oceanic crust to be recycled back into the Earth's mantle. As a result, rocks older than 200 million years are not found in the oceans because they have been subducted and destroyed in the mantle.

Answer:

Rocks older than 200 million years are not found in the oceans because the oceanic crust is recycled through plate - tectonic processes. New crust is formed at mid - ocean ridges and older crust is subducted at subduction zones, being destroyed in the Earth's mantle.