If all ocean floors are newly formed due to expansion, then we need to explain how these enormous rifts have been filled so perfectly with salt water. The amount of water is neither more nor less than what has been required to fill the rifts.
The only way this could be the case, short of a miraculous coincidence, is that the water has come from inside our planet. If it came from outside our planet, the coordination between expansion and water supply would be impossible. There is no way the heavens could be coordinated in such a way that they supply water at the exact rate of planetary expansion.
Furthermore, comet tails have water rich in deuterium. They are therefore not the source of water on Earth.
The abundance of salt in our oceans is further evidence that the water came from within our planet which has huge salt domes hidden deep below its crust.
If the expansion of our planet is due to radiation, as suggested in this book, then water may even be synthesized inside our planet as a part of the expansion process. Heavy elements split off hydrogen and oxygen atoms as they decay through radiation. The result is water.
From observing rifts and volcanoes, water vapour appears to be an abundant component of their venting. All evidence point to Earth as the source of salt water in the oceans.