troposphere is the layer closest to the earth, and it is the
layer in which we live. It is about ten miles deep. Seventy five
percent of the mass of all our atmospheric molecules is in the
troposphere, and this is where we find water vapor, dust, pollen,
and soot particles. Weather happens in the troposphere. This
layer is turbulent, with storms and atmospheric mixing.
This diagram shows the different
In the troposphere, the air cools gradually as
it gets further from the earth. At the very top of this layer
the air temperature is about 76 degrees below zero on the Fahrenheit
scale. This is important, because it changes water vapor into
ice, forming the cold trap, a temperature region where
water vapor stops going up. If we had no cold trap, water molecules
could rise in the atmosphere where they would eventually break
down into oxygen and hydrogen. The small, light hydrogen molecules
could then escape into space. Earth would loose its water if
we had no cold trap.
The stratosphere lies
above the troposphere. It is about twenty miles deep. The stratosphere
contains about 24% of the mass of all the atmospheric molecules.
This layer has the ozone layer in it. The ozone layer protects
all life on earth from the harmful and potentially even lethal
ultraviolet radiation emitted by the sun. There is not very much
ozone -- if it were all together, it would form a layer only
three millimeters thick. Three millimeters is not quite this
deep: __ .
The lower part of the stratosphere
is cold, but it warms up as it gets farther from the earth --
another effect of the ozone. This layer is peaceful compared
to the troposphere. If you have been watching the math, you see
- The troposphere is 10 miles deep and has 75% of the mass
of the atmosphere
- The stratosphere is 20 miles deep and has 24% of the mass
of the atmosphere
This means that the lowest 30 miles of the atmosphere has
99% of the mass of the molecules! However, the atmosphere goes
out to 40,000 miles. It makes sense, then, that the atmospheric
molecules get farther and farther apart from each other as they
go up the remaining 39,970 miles, and that is just what they
do. Although there are some atmospheric molecules up here, they
are scattered and occasional, not like our thick ocean of air
close to the surface.
The entire atmosphere of the
earth extends out about 40,000 miles above the earth -- and the
earth is about 8000 miles across. The moon is a little less than
240,000 miles away.
The Relative Positions of the Earth, the Atmosphere,
and the Moon.
Sites to visit for more information:
Text about earth's atmosphere with an important graph. Be
sure and read this one.
Adult text description of the atmosphere. OK for the lay person.
There is a lot of good information at this attractive site.
Somewhat less detailed description of the atmosphere than
the instructor notes above. Good information. There are easier
reading levels containing this information at the same site.