Final answer:
Seafloor spreading is the process that forms new crust as magma pushes through the lithosphere due to convection currents, while subduction is where crust is recycled into the mantle as one plate goes beneath another at convergent boundaries.
Step-by-step explanation:
The process where energy from the core creates convection currents that push magma through the lithosphere at a boundary to form new crust is called seafloor spreading. This process contributes to the constant recycling of Earth's crust, as new material is added and old crust is pushed towards the boundary. Subduction is the process where the crust is moved towards a boundary and recycled as it is pushed down by gravity into the mantle. Subduction often occurs at ocean trenches, such as the Japan trench, where an oceanic plate is thrust beneath a continental plate or another oceanic plate.
In a subduction zone, the old crust is forced into regions of high pressure and temperature, melts and becomes part of a downward-flowing convection current, which helps to balance the creation of crust at divergent boundaries like rift zones. Overall, the amount of crust destroyed at subduction zones is approximately equal to the amount formed at rift zones, maintaining a balance in the crustal material.