With the pressure, as you go higher from the surface of the atmosphere, you are "loosing" pressure.
Just for example of HOW MUCH MORE pressure you place on yourself by going under water, the pressure you feel on your body (especially ears) doubles every 33 feet. Here is a very simple diagram:
xxxxx - space = 0 Atmosphere's of pressure
----- - surface of earth = 1 Atmosphere's of pressure
-33- - 33 feet under water = 2 Atmosphere's of pressure
-66- - 66 feet of water = 3 Atmosphere's of pressure
-99- - 99 feet of water = 4 Atmosphere's of pressure
You notice a bigger change from 0 to 33 feet when diving because the pressure felt doubles in a pretty short time period. You notice a much more gradual increase going from 33 feet on down, even though the pressure is building at the same rate, it does not "double" again until 99 feet.