I was thinking more of the math required to account for all the water.Math being the most plausible one, I guess if life on earth got wiped out by a flood and only 5/6 people survived, could we get to where we are in 4000 or so years?
The earth is a sphere that is approximately 41,807,000 feet in diameter at sea level. If you covered every point on Earth with water, it would need to be a sphere at least 41,865,032 feet in diameter (to cover the highest mountains.) You can calculate the volumes of those two spheres and subtract them. That gives you over a billion cubic miles of water you would need to add to the Earth to cover the tallest mountains. There are only 332 million cubic miles of water on the entire Earth.
So problem one is you would have to claim that over a billion cubic miles of water just appeared from somewhere. Even if you evaporated every bit of every ocean, lake and river on Earth and had it fall as rain, you'd still only have a third of that. (And of course it would run right back into those ocean and lake basins.)
And problem two is that you would then have to claim that, after it fell from somewhere, it all magically disappeared again.
The repopulate the planet from 6 people isn't impossible numerically. If every couple had 6 kids starting at age 20 you could get from 6 people to 8 billion in about 500 years. Needless to say there would be HUGE genetic problems from inbreeding but it's possible in theory.