1. The problem statement, all variables and given/known data It has been estimated that the mass of nitrogen alone in the column of atomsphere above each square metre of the Earth's surface amounts to about 8 tonnes. Why aren't we crushed by this? 2. Relevant equations none 3. The attempt at a solution Air in the atomsphere is not just nitrogen and they are dense as the question suggested. Are we are not crushed by them essentially because of Newton's third law? We are surrounded by dense air in ground level. What kind of molcules are they? They surround us and collide with our bodies and make us not as cold if without them. The different densities of air all exert forces to the next layer and due to the third law there is an upward force from the succeeding layers. These layers does the same and you get somewhat of a cancellation of forces on each layer. Hence equilibrium is reached for each layer as there is no net force and we are not crushed by the upper level air. So a cushioning effect is passed down through the layers. The image tries to illustrate this.