@glitterbag,
Hahahaha, you don't like my awesome drawings?
I'll have you know that I was a C student in my 6th grade art class.
The point is, these (shitty) drawings are based on what we already know about the layers of atmosphere, and the layers of ocean and underground. Aside from the flat earth thing, this is identical to the less shitty drawings of Earth's rock layers...
(as you can see, rock tapers off into a molten liquid area, followed by solid mass again, sorta a yummy lava sandwich)
Earth's water layers...
and Earth's atmosphere...
These too are "cartoons" as you put them, but you believe them because people in snazzy costumes tell you they are scientists and you should believe what they say.
What these scientist will tell you though, is that the deeper in the ocean, the higher the pressure, and the heavier you need to be, both to stand up to the intense pressure of the water and to sink to such depths. Likewise, the air gets thinner as you climb mountains. You get decompression sickness, both from emerging too fast from underwater and from climbing a mountain like Everest too quickly. It's a pressure change affecting the body. In other words, there is NO difference between ascent in water and ascent in air. Pressure, not gravity, is what determines whether objects fall or float.