There are few databases in science more comprehensive than weather. Mention of floods and droughts appear in ancient hieroglyphics, engraved symbolically on everything from clay pots to stone-tipped spear shafts, and can be inferred by images on cave walls millennia earlier. Temperature and pressure data were written down starting the very day those first crude instruments were created.
Humans have paid great attention to weather for good reason: The ebb and flow of the seasons govern all life, an active sky stretches over the forests and deserts, so different and yet so familiar, like a gaudy pastel cartoon. Clear or cloudy by day, decorated with a menagerie of stationary and moving lights at night, there was always a great show overhead. Even domestic fire itself, arguably the most important single development in the early evolution of our kind and our closest hominid cousins, was probably first delivered in dramatic fashion by cracks of lightning. It's no wonder we call it Heaven.
Which brings up a soon-to-be-released motion picture and the depiction of a notion discarded long ago by Earth scientists. The flood of Noah, explored beneath the fold.
Could it have happened? Could it rain so hard and long on a terrestrial world that the tallest mountains were under water? Sure, it could ... just not on Earth and especially not in the last few thousand years. There are plenty of reasons why, starting with the fact that there's not enough water held in the atmosphere at any given time and, unless the planet's air was converted into a thick, broiling steamy version of Venus that would sterilize the entire surface of land and sea alike, it's not possible for our atmosphere to hold even a tiny fraction of the necessary water vapor required to produce thousands of feet of rainfall.
We know this. It's not a matter of opinion, it's a matter of well-established and tested physical properties of heat, pressure, water and vapor. Not to mention some simple geometry.
Bear in mind, the water has to come from somewhere besides the ocean. The reason sea levels are what they are is a combination of how much liquid water exists on Earth and the fact that the ocean basins are the lowest parts of the planet. No matter how that liquid is distributed initially, it will quickly fill up the lowest points: water runs downhill.
The Earth is so close to round that we can use a circle or globe to stand in for it when figuring out how much water it would take to reach the summit of various mountains. We'll spare you the math and provide the simple answer: over half a billion and a billion cubic miles of additional water would be needed to submerge the peaks of the more modest mountains in Noah's region or the Himalayas, respectively. At any given time and averaged over the entire planet's surface, the atmosphere can hold ... mere inches of the wet stuff at the most. The whole reason it rains anywhere, ever, is because the amount of vapor in the air regularly and locally tests this limit by exceeding the carrying capacity of the air mass in which it is embedded and condenses out as droplets.
To get our atmosphere to hold even the equivalent of a few feet of additional water, enough to raise global sea levels measurably, it would have to be very hot and very dense and composed almost entirely of water vapor. As the old saying goes, Noah would have been poached long before he could move, let alone work on a big wooden ship for 70 years. It also couldn't have come from space in the last few thousand years. An object or objects representing that volume of water would be equivalent to an icy asteroid hundreds of miles in diameter striking the planet. It wouldn't matter if it was fluffy snow, it wouldn't matter if it were super light Styrofoam—that kind of mass hitting the surface at orbital velocity would be the end of life. Maybe some scattered lucky microbes would survive, maybe. Nothing else would.
If one needs a basis for legend, in this case a massive local flood, there are more likely explanations. If we presume Noah lived around 5,000 or 6,000 years ago, he would have been smack dab in the middle of the last stages of a great global warming trend caused by the retreat of the most recent glaciers. In some places weather would be chaotic, sea levels would have been rising, maybe fast enough for a Neolithic tribe living near the coast to notice in the course of a single lifetime. Myths might have sprung up to explain this, and in that cultural environment, when the inevitable flood of a lifetime came and one family managed to ride it out for days on a raft with a few chickens, it would have made quite an epic story to tell and re-tell.
All that being said, as a modern movie-going people, there's no reason to insist on perfect scientific accuracy in a film based on legend. Such criteria would eliminate virtually every sci-fi flick ever made, let alone some of the best fantasy and adventure films ever recorded. After all, Thor wasn't half bad and the Tolkien movies were great. Maybe Noah will be tolerable, perhaps even entertaining. As long as skepticism about magic hammers, actual evil rings or real global floods don't ruin the fun!