"describe how plate tectonics both creates and destroys earth's crust."

Creation:When rising convection current of magma reach the surface,it push the plates apart along the crack,the welling magma would then fill the crack and eventually cools down to be new crust material.

Destruction: When sinking convection current of magma occurs,the plates would collide. Under the pull of gravity,the denser of the two would sink below the other and meltdown,being destroyed.

hope it helps!