Sure but once a continental plate is flooded, isn't it by definition an oceanic plate at that point? A continent only exists if it isn't flooded.

Thanks for all the detail! Your observation about comets is really pertinent. Saltwater is probably itself a purer form of water than comets. Maybe an ocean planet is actually more like a muddy swamp of nasty dirty water than a lake.

Exactly. If a planet ever had a salty ocean, adding more water probably wouldn't dilute it in any meaningful way, so it would need to be a planet that never had continents.

That is super interesting! I hope the Clipper gives us a definitive answer!

I was trying to figure out how much underwater erosion there is but if you compare the sandy and silty bottom of the ocean to like, Utah, it seems like continental erosion is orders of magnitude more significant.

Conversely, we know oceans deposit all sorts of stuff at their bottoms, which makes me think there is a small amount of salt being deposited. Would that cancel out significant underwater erosion?

Similarly, if underwater erosion was a big deal, wouldn't old lakes (in geological time) be notably saltier than young lakes? But the only salty lakes we have primarily lose all their water through evaporation, basically ultra concentrated river water.