Why does the size of the earth remain the same despite of what happens at the mid-oceanic redges?

Answer 1

Think of it like a pot of boiling soup, if you look at the pot of boiling soup there are areas where the soup is bubbling up to the top but ASLO other areas where the soup is moving back down to the base of the pot (it is called convection) - the soup pot does not have to get wider!.

Well the Earth behaves in the same way. The mid-oceanic ridges are places where the hot internal rocks are rising up to make new oceanic sea floor crust, but around the edges of the ocean there are other areas where could sea floor crust is sinking back into the middle of the Earth. These areas are called the deep ocean trenches (or subduction zones) such as the Marianas Trench. Thus, overall the everything is kept in balance and the size of the Earth remains constant. Note also that there are places on the Earth where instead of crust sinking back into the middle of the Earth, continents crash into one another and when they do this the crustal rocks become folded and mountains are formed - again the process of mountain building balances out the spreading that happens at the mid-oceanic ridges.