What geological or physical mechanism could make the Earth grow?
How could planet Earth expand?
With the areas between filled with new rock from sea floor spreading at mid ocean ridges?
And geologically relatively recently?
Ocean crust is a very different material to continental crust.
Oceanic crust underlies most of the two-thirds of the Earth’s surface which is covered by the oceans. It has a remarkably uniform composition (mostly 49% ± 2% SiO2) and thickness (mostly 7 ± 1 km).
The ocean floor is the most dynamic part of the Earth’s surface. As a result, no part of the oceanic crust existing today is more than 200 million years old, which is less than 5% of the age of the Earth itself.
British Antarctic Survey - Oceanic Crust