I still have questions

M-Earth could hold slightly more atmosphere than Venus of a given composition. It's geo and atmospheric chemistry not physics that dictates much of the difference not gravity. Venus and Earth have similar carbon inventories. Most of Venus' is in its atmosphere while Earth's is tied up in rock. Venus has no water due to its high temperature. On Earth water converts CO2 (the prime componant of Venus and Mars' atmosphere) to carbonic acid which forms carbonate minerals when neutralized.
J- I assume that when the planets Earth and Venus formed, they both got about the same amount of CO2 in their atmospheres. I wonder how long it takes for this carbonate mineral formation to remove such a huge amount of CO2 from the atmosphere. Would it have been possible for the dinosaurs to live during a time when there still existed huge quantities of CO2 in the atmosphere? CO2 has a higher density than Nitrogen, therefore it would excert a higher pressure on everything immersed in it.
J-- Is it bouyancy or something else that keeps the hovercrafts 'up in the air' so to speak? How high is the pressure under the hovercraft?
M-I think hovercraft use jets of air not bouyancy. Balloons use bouyancy.
J-Sorry about the error, the word is spelled BUOYANCY and is part of Archimedes Principle. I think that the fans on the hovercraft create a higher density of air (pressure) underneath the craft thereby buoying the craft upward.
J--How can life exist in the deepest parts of the oceans?
M-They use gills not lungs. Gills don't inflate and deflate against pressure.
J-I surmised that if the (fluid) pressure was equal on the inside and the outside of the lungs, the energy reguired to deviate the difference sufficiently for respiration purposes would be minimal.
M-Most planet formation models are based on Earth being built from solid planetisimals similar to asteroids and comets. Gas Giants formed similarly but at a point where abundant volatiles were available to be trapped by the growing planets gravity as it grew in size.
J-How did these planetisimals happen to be orbiting the Sun, how did they form. Are you saying that these planetisimals that created the Earth could not have trapped gasses during the planet formation? Are you also saying that volatiles only existed in the area of the gas giants; if so, what was the physical laws that prevented the volatiles from being in the vicinity of the Earth formation?
Cheers
Johannes