Design of Air

If the atmosphere's values of density, fluidity, and pressure were altered by even a fraction, inhaling would become as hard as drawing honey into a syringe. One could argue that the syringe's needle could be made wider, in other words, the lung's airways could be enlarged. But if we did that in the case of the capillaries in the lungs, the result would be to reduce the size of the area in contact with air, with the result that less oxygen and carbon dioxide would be exchanged in the same amount of time and the respiratory needs of the body would not be satisfied. The air we breathe in has the absolutely right density, fluidity and pressure and fits the bill just fine. On this subject, Professor Michael Denton states the following:

It is clear that if either the viscosity or the density of air were much greater, the airway resistance would be prohibitive and no conceivable redesign of the respiratory system would be capable of delivering sufficient oxygen to a metabolically active air-breathing organism... By plotting all possible atmospheric pressures against all possible oxygen contents, it becomes clear that there is only one unique tiny area... where all the various conditions for life are satisfied... It is surely of enormous significance that several essential conditions are satisfied in this one tiny region in the space of all possible atmospheres. (Michael Denton, Nature's Destiny, The New York: The Free Press, 1998, p. 127.)

Our atmosphere's properties must be right not only for respiration purposes, but also to keep our "blue planet" blue. If the pressure were to be decreased by as little as a fifth, water evaporation over the land and oceans would increase dramatically. Higher water vapor content in the atmosphere would create a global greenhouse effect, dramatically increasing the planet's average temperature. On the other hand, if the atmospheric pressure doubled, water vapor in the atmosphere would be greatly reduced, with most of the world's land area becoming desert.