So, Here's the scenario:
we start with an ocean planet, with minimal dry land. The planet stays this way for at least 400 million years. (Notably, life evolves during this time period.) Then, a magic portal opens at the bottom of the sea, and drains a large portion of the water into space. The portal closes when the land-to-sea ratio of this planet is roughly the same as Earth's.
I'd like to have another magic portal open at this point so that Earth land life can colonize the new land. However, as I learned from my last post on the subject, the land would likely be far too salty for plants to establish themselves. (What would an until-recently waterworld look like?)
This question may also be relevant: (How to dry an ocean planet and turn it into a salty desert?)
so... what natural event could reduce the salt levels on the land such that plant life from earth could establish itself? If that natural event is simply a lot of time, how much time?
Bonus question: after all this is said and done, how would the land on this planet differ from the land on earth? at what point in their technological history would humans, if they came over with the other animals during the stone age, be able to tell that the planet was submerged for most of it's history?