I am trying to figure out ways to determine the density and composition of an Earth-like planet. For the sake of the "experiment", let's assume that the planet is identical to Earth in every physical way except it is 1.25 times the mass. If the Earth's atmospheric composition is 78% Nitrogen, 21% Oxygen and the rest various other gases, what would the atmospheric composition be if the planet were more massive?
Let's further assume that the planet formed in the same way and the moon came about the same way.
What I am curious about is: does this difference cause far lighter elements to be in the atmosphere due to a higher escape velocity? And if so, would the gravity cause a greater atmospheric pressure?