did the mariana trench exist pre-flood or during?
What would happen if the ocean floors were to be upheaved to our present sea level?
If there was only one supercontinent, why would one assume Everest OR the Mariana trench, either one, would exist?
Why are you assuming one supercontinent? The continents aren’t ‘floating’ or loose. If you look at where some of the plate boundaries are they are nowhere near the edge of continents.