How about these premises?:
The Earth is 4.5 billion years old.
C. 4500 years ago it rained hard all over the Earth, for 40 days and nights, because God made it such. Let's not worry about the water source, the temperature effects of condensation, etc. There were also be other water sources, but let's not sweat such details. Just say God was directly adding volume to the oceans.
This resulted in sea level rising, say, 3000 feet (or 1000 metres if you prefer) over those 40 days.
Then over the next year (or pick you own time period) the water drained to the ocean basins, where God removed it back to wherever s/he stores that extra supply of water.
Now, what was the nature of the Earth, as opposed to pre-flood?
Adminnemooseus