Is Earth Full of Water?

Oceans are far younger then continents. While continent are roughly 6000 million years old, no ocean is more than about 300 million years old. It is therefore reasonable to suggest that our planet has expanded, and that oceans are the stretched areas between the original crust that are today's continents.

But how is it that our oceans are so perfectly filled with water? If the water came from space, it would be a truly astonishing coincidence that the quantity so exactly matches the volume required to fill the oceans neither too much nor too little.

A more reasonable explanation would be that the water originates from inside our planet, that the water, together with salt and other minerals, were squeezed out as the seafloor was stretched out between the continents.

Can Earth be likened to a sponge saturated with water, where the stretched areas has forced water to the surface, creating oceans, while the continents, where no stretching have occurred, have remained dry?

Earth expansion seen from the south pole