That gas pressure could be understood most easily if we assume that
the air around us and the air in our atmosphere is at constant temperature.
That's not exactly true the, as we'll see soon.
The temperature of our atmosphere decreases as we go up.
But in order to make our calculation simple,
we're going to make the approximation that the atmosphere of the Earth and
the atmosphere of Mars are Isothermal.
Isothermal means constant temperature.
If you're Isothermal and we call the pressures equals to density times
temperature, the change in pressure, from the bottom of the atmosphere
to the top will go as the change in density times these constants and
the fact that we're keeping temperature constant means for giving.