Composition & Structure of Atmosphere:1
Composition and Structure of the Atmosphere
Let’s continue looking at Earth’s climate and what controls it.
We have already
seen what causes the seasons and we will bring that up over the next few
As a bit of background,
refers to the short term conditions of the
atmosphere, at time scales of hours, days and weeks.
refers to the long
term conditions, where averages are more important.
Today’s weather may be
sunny and hot in Lubbock, but our climate is semi arid.
Today’ we may get rain,
that’s weather, but average rain this month is X mm and that is a climatic
Today we are concentrating on the atmosphere itself: what’s there and how is it
Thickness of the Atmosphere
There is no definitive answer to how high the atmosphere is.
The gases are
densest near the surface and get less dense with altitude.
At 16 km, the air is
10% as dense as at the surface and at 50 km, it is 1%.
There is almost no gas
found above 100 km, but some exists.
Composition of the Atmosphere
The gases that make up the atmosphere (some liquid and solid material is also
found, as we will see) are thought of as either permanent or variable.
gases are in the air at relatively constant proportions in both time and space,
while the amounts of the variable gases change.
Oxygen, a permanent gas, is
roughly the same the world over and has been pretty much the same for millions
Water vapor on the other hand can vary considerably from place to
place and day to day.
are mostly nitrogen (78%), oxygen (just less than 21%)
and argon (just less than 1%).
While these percentages stay pretty constant,
many of these substances are being cycled with the solid Earth.
Some plants, for
example, take nitrogen out of the air and leave it in the soil, where it is an
important nutrient for other plants.
As plants die, the nitrogen is returned to the
Oxygen is taken out by breathing animals and other processes and it, too,
gets returned to the atmosphere.
The cycling of oxygen is much faster than the
cycling of nitrogen.
It is estimated that a typical oxygen molecule is in the air for
5000 years before being taken out, while nitrogen lasts for 42 million years.