Religious debate via Meme

[downbeatplumb]

That's possible, with the land pushing up through the water later.  It's not quite the same as having a bunch of water hiding somewhere inside the earth's mantle, though.

If you look at the data, it seems fairly certain, that there is water within the earths mantle.   The fuzzy part, I believe is in estimating how much exactly there is. However the concensus does seem to be a lot.  

However, this discussion probably doesn't belong in the meme thread.

Well there is water there but not in vast deposits. Its held high pressure minerals.

or many years, scientists have attempted to establish exactly how much water may be cycling between the Earth’s surface and interior reservoirs through the action of plate tectonics. Northwestern University geophysicist Steve Jacobsen and University of New Mexico seismologist Brandon Schmandt have found deep pockets of magma around 400 miles beneath North America — a strong indicator of the presence of H₂O stored in the crystal structure of at these depths.

So think of it more as damp sand than an ocean waiting to burst forth.

https://www.astrobio.net/news-exclusive/scientists-detect-evidence-oceans-worth-water-earths-mantle/