Why do we assume that water came from outside the Earth? We have recently discovered there is more water within the Earth then on the surface.
At this point isn’t it logical to deduce that flooding could just as easily result from certain tectonic movements underground resulting in an up welling of water from subterranean reservoirs?
I’m not saying that water couldn’t also come from outer space, or a melting of the ice, however it seems far more likely with recent findings that it could just as easily if not more easily emerge from underground based on the dynamic movement of tectonic plates.
You could also think of Earth like a sponge. Due to shifting pressure differential from tectonic activity, an underground reservoir may be “squeezed out” of it’s currently enclosed area and in to an ocean through cracks or tunnels that lead to the surface.
An interesting theory nonetheless. Perhaps I will add to this article as I conduct further research.