Year 9 Geology question

Question

At some divergent boundaries, volcanic eruptions along mid-ocean ridges are continually creating new oceanic crust. This causes the seafloor to slowly spread away from the ridges. But the Earth's crust is not getting any bigger.

Explain how this can be true, using your knowledge of the different types of plate boundary.

Answer 1

Earth doesn't get any bigger because there is an equal amount of crust being lost when subducting plates melt at convergent boundaries somewhere else on Earth.