Why does the earths surface not get any smaller or larger using divergent and convent plate boundarys?

The Earth's surface remains relatively constant in size due to the processes occurring at divergent and convergent plate boundaries. At divergent boundaries, tectonic plates move apart, allowing magma to rise and create new crust, which offsets the surface area lost at convergent boundaries where plates collide and one is subducted into the mantle. This recycling of crust ensures that, overall, the Earth's surface area remains stable. Thus, any new crust formed at divergent boundaries is balanced by crust being destroyed at convergent boundaries.