The idea that magma rises up at rift valleys and crust is being destroyed at trenches describes the theory of

The idea that magma rises up at rift valleys and crust is being destroyed at trenches describes the theory of plate tectonics. It is a theory where the lithosphere is being divided into plates. These plates are a result of the continuous rising of magma causing the crust and rift valleys to be destroyed. These plates continuously moves and the movement is a result of the convection process in the mantle. Hot substances near the core would rise up while the colder part would sink. The convection would push and spread apart ocean ridges. Also, it pulls and sinks subduction zones.

How are period and frequency related to each other? dperiod is the reciprocal of frequency.