Earth's Atmosphere
The atmosphere is a thin blanket of gases, mostly nitrogen and oxygen, that surrounds
the earth and is held in place by the earth s gravity. All of the weather that we
experience occurs within 7 miles of the earth s surface. In this section, we will discuss
some of the basic characteristics of our atmosphere.
Layers of the atmosphere
The earth s atmosphere extends upward many hundreds of miles and is divided into five
basic layers with narrow boundaries between the bottom four layers (see Table 1-1).
Layer or
Remarks
Boundary
Troposhere
Extends upwards from the earth s surface approximately 7 miles. All
weather occurs in this layer.
Stratosphere
Extends upwards to approximately 30 miles. Temperature increases
with height. Ozone concentration is heaviest in this layer.
Mesosphere
Extends upwards from the stratopause approximately 50 miles.
Temperature decreases with height.
Thermosphere Extends upwards to approximately 70 miles. Temperature increases
with height.
Exosphere
Outermost layer of Earth s atmosphere. Composed of hydrogen and
helium.
Tropopause
Boundary separating the troposphere and the stratosphere. Height
varies, normally found at higher elevations near equatorial regions and
at lower elevations near the North and South poles. Jet stream occurs
in the tropopause.
Stratopause
Boundary between the stratosphere and mesosphere, typically at 30
miles.
Coldest place on Earth with an average temperature of -120o F. Due to
Mesopause
cold temperatures, water vapor freezes and forms ice clouds.
Table 1-1 -- Layers of the atmosphere
A vertical cross section of the earth's atmosphere is depicted in Figure 1-1.
1-2
