Thickness of Earth's atmosphere

1. Feb 1, 2009

elliotyang

1. The problem statement, all variables and given/known data
Calculate the thickness of Earth's atmosphere.
Assume that the pressure and temperature do not vary with height.
Make reasonable assumptions for their values.

2. Relevant equations
I think this question has to be solve with ideal gas equation which is PV=nRT

3. The attempt at a solution
Since the problem stated that the pressure and temperature do not vary with height,
so I assume it is stp which pressure is 1atm, and 25。c (I suppose the absolute temperature for ideal gas law to be 273 K, but it seems to be impractical and not consistent with the problem).
then i stuck, i do not know how to obtain the value for n.