Re: space being a vacuum..why doesn't it take our air???

The simple answer is gravity.  Gas may flow towards a vacuum, but gravity
holds it to the earth.  What you see as you increase your altitude is that
the air becomes steadily thinner because most of the air is held close to
the earth by gravity.  So it's not a question of the vacuum of space sucking
the air out of the atmosphere, but more the earth's gravity holding as much
of the air as close to the earth as it can.

The earth does lose some air continuously, but because of heating.  In the
upper atmosphere, the distance between individual atoms or molecules is
pretty large and the temperatures are very high.  Since temperature of gas
molecules is simply a measure of their average energy, this means that
high-temperature gas molecules are moving at high speeds.  In the upper
atmosphere, they can be moving quickly enough to reach escape velocity and,
with no other molecules nearby to slow them down, they can escape into outer
space.  Something like this helped to remove just about all the hydrogen
from the earth's atmosphere early in the history of the planet.

You can find more details about both of these phenomena in most introductory
books about astronomy or atmospheric science.  In addition, "Planet Earth"
(Cesare Emiliani, Cambridge University Press, 1992) gives a good general
discussion of this topic and "The Chemical Evolution of the Atmosphere and
Oceans" (Heinrich Holland, Princeton University Press, 1984) gives a much
more detailed and technical account.  Both are excellent books, but
Holland's is not for the scientifically faint of heart.  Emiliani's, on the
other hand, is an excellent general reference for many questions about the
earth and its history.