Anug -
First question first. Another word for the sky is the Earth's
atmosphere. The atmosphere is made up of air, which is composed of a
number of different gases, the most important of which (at least to us)
are nitrogen (78%), oxygen (21%), and carbon dioxide (0.033%). There's
also argon (0.93%), neon (0.0018%), and smaller amounts of helium,
krypton, xenon, hydrogen, methane, etc. (From the
Tech Expo.)
Up high in the atmosphere, just before you reach open space, there's
also a layer that contains a lot of ozone (the "ozone layer"), followed
by a layer containing a lot of miscellaneous ions (the "ionosphere").
As for the second question, the sky sure will drop down! At least
it will continue to do so, since it already has. And it's a fortunate
thing, too. If the atmosphere wasn't held down near the ground by
gravity, the air would just spread out through space and we'd have
nothing to breathe. Gravity holds the atmosphere against the Earth, but
the air is light enough and has enough energy of its own that it
doesn't get compressed all the way against the ground under our feet.
-Tamara
(published on 10/22/2007)
