Pete..." How do you know there was not enough water below to augment that from above."?

Avoiding for a moment reminding you that YOU have no way of knowing and having records of how things were in "deep time"........(no, old religious tracts are not evidence. Who would have seen that happen and lived to write it down?)

First, elementary arithmetic. We have X amount of water now, and there's no math I can see that would explain where it went after drowning everything.

Second, 'below' is a pretty hot place. Water that does manage to get 'below' is heated and finds its way back up in places like out Yellowstone Park.

Third, there's no reason in physics and geology that water would BE below in such large quantities. There are large aquifers in places, but that water began ^above and gradually seeped down.