text: All gases stay within the atmosphere of earth and are not scattered out to space. Earth's gravity is responsible for this.\n\nThe escape velocity v (minimum velocity required by a body to escape out of the Earth's gravitational field) is a function of the acceleration due to gravity g. Now, if the root-mean-square (RMS) speed of the gas particles (atoms and molecules) is less than v, obviously they can not escape the Earth's gravity. All gases which are present in the atmosphere satisfy this condition and therefore they stay with the Earth.