Layers of the Atmosphere
Key Questions:
 What are the four main layers of the atmosphere?
 What are some characteristics of each layer?
The atmosphere can be divided into four main layers based on the temperature changes that
occur as altitude increase. Temperature variations in the four layers are due to the way solar
radiation is absorbed as it moves downward through the atmosphere. The Earth’s surface is the
primary absorber of solar radiation. Some of this energy is re-radiated by the Earth as heat,
which warms the air near the ground.
The layer closest to the Earth is called the troposphere. It is about 16 kilometers thick above
the equator but only 9 km thick above the North and South Poles. Most weather occurs in this
layer because gravity keeps most air molecules in it. The jet stream is located at the top of this
layer which is also where commercial airplanes fly. The average temperature in the troposphere
rapidly decreases with altitude until the tropopause; the boundary between the troposphere and
next layer.
The second layer is called the stratosphere. In this layer, which extends from the top of the
troposphere to about 50 km, the temperature begins to increase with altitude. This warming is
caused by a form of oxygen called ozone (03) that absorbs ultraviolet radiation from the sun. This
layer of ozone high in the stratosphere protects living things from most of the sun’s ultraviolet
radiation that can cause sunburn and lead to cancer. Human activities have led to a decrease in
the amount of ozone in the stratosphere but recent changes have helped that ‘hole’ recover
slightly. This ozone layer is located near the stratopause, which is the boundary between the
stratosphere and the next layer.
In the third layer, called the mesosphere the temperature begins to decrease with altitude
because it does not absorb solar radiation. In fact, it is the coldest layer. The mesosphere
stretches from the top stratopause (about 50 km) to about 80 km. Most meteoroids burn up in
this layer producing ‘shooting stars’. The top boundary of this layer is called the mesopause.
In the last layer the temperature once again begins to increase with altitude. This layer is
the thermosphere. Here solar radiation first hits the Earth’s atmosphere and heats it. Because
the atmosphere is so thin, a thermometer cannot measure the temperature accurately and
special instruments are needed. This layer is divided into two sub layers. The first is called the
ionosphere (about 80 km to about 400 km). In this layer, radio waves bounce off ions (which are
gas molecules that the suns energy has electrically charged). These ions can collide with atoms
and produce the northern lights. The second layer is the exosphere. It extends from about 400
km on.
Directions:
1. Use the points in the data table to make a line graph of temperatures at various altitudes.
2. Label the boundaries for each layer (tropopause, stratopause, mesopause).
3. Label each layer.
4. Lightly color each layer (1st layer – orange, 2nd layer – yellow, 3rd layer – blue, 4th layer – green).
5. Read pages 17-22 in the textbook and add two pictures to each layer that shows a
characteristic of that layer.