What about things in Genesis that we now know are not true? For instance:
And God said: Let there be a firmament made amidst the waters: and let it divide the waters from the waters. And God made a firmament, and divided the waters that were under the firmament, from those that were above the firmament, and it was so. And God called the firmament, Heaven; and the evening and morning were the second day.
We know that the sky (the "Heavens") is not made up of water behind a firmament.
That's where you're wrong.
It's not any MORE, but it certainly was before the Flood.
There used to be a massive water canopy enveloping the earth, blocking 99.999% of the UV rays, causing MUCH higher barometric pressure and allowing for larger creatures. The higher pressure, as well as the higher oxygen levels in the air, made man EXTREMELY vigorous to the point that he lived 800-900+ years.
If you look at the human body, and its regenerative abilities, one would conclude that it was designed to last virtually forever. Certainly longer than 60-80 years. We're practically dying in our infancy now.
Just when a man finishes his education and fully "grows up" in every department (around 50), his body begins falling apart and he's dead within 2 decades. Tragic, really.