Layers of the Atmosphere
Integrated Science 1 Name: Date: Pd:
Background:
The atmosphere can be divided into four layers based on temperature variations. Since each layer is based upon temperature
changes, the layers are separated in unequal distances. The layer closest to the Earth, and with the lowest altitude, is called the
troposphere. Above this layer is the stratosphere, followed by the mesosphere, then the thermosphere. The upper boundaries
between these layers are known as the tropopause, the stratopause, and the mesopause. Temperature variations in the four
layers are due to the way solar energy is absorbed as it moves downward through the atmosphere.
TROPOSHERE – The troposphere is the layer immediate above the surface of the earth. The Earth’s surface (land and oceans)
is the primary absorber of solar energy, specifically UV (ultra-violet) radiation. Some of this energy is reradiated by the Earth
as heat in the form of infrared radiation (IR) , which warms the overlying troposphere. The average temperature in the
troposphere rapidly decreases with altitude, until at the tropopause, the boundary between the troposphere and the stratosphere.
The jetstream is located at the tropopause.
Since gravity is strongest near the Earth’s surface, the troposphere has the majority of the Earth’s gas molecules and aerosols,
especially water. The density of gas is instrumental in flying commercial aircraft, as most can not fly higher than the
troposphere. The troposphere is also where all of the World’s weather occurs. All mountains, even Mount Everest all exist
inside the troposphere
STRATOSPHERE - The temperature remains constant for the first 10 km, until it begins to increase with altitude in the
stratosphere. This warming is caused by a form of oxygen called ozone (O3). Ozone protects us from most of the sun’s
ultraviolet radiation, which can cause cancer, genetic mutations, and sunburn. The oxygen molecule (O2) normally consists of
two oxygen atoms. To break these molecules apart requires a lot of energy, which comes from absorbing solar UV radiation.
The stranded oxygen atom then fuse (join) with another O2 molecule, forming ozone (O3). Oxygen does not like having three
molecules bonded, as in ozone, and to keep the ozone together requires a lot of energy, which again is absorbed from the solar
UV radiation. Through this whole process, ozone absorbs approximately 25% of the ultraviolet radiation from the sun. The
ozone layer begins at the increase in temperature in the stratosphere and is, on average, 10 km thick. At the stratopause, the
temperature stops increasing with altitude.
Only specially designed aircraft, such as the Concorde (the World’s fastest commercial airliner), or the SR-71 Blackbird can
fly in the stratosphere. This is the highest layer that weather balloons can fly.
MESOSPHERE - The mesosphere does not absorb solar radiation, so the temperature decreases with altitude. The mesosphere
reaches the coldest temperatures in the atmosphere, down to -90°C (-130°F). The start of the coldest readings is called the
mesopause.
Though the spacing between molecules is great in the mesosphere, themolecules are closer compared to the overlying
thermosphere. This causes asteroids to turn into the meteors, “falling stars”, within this layer.
THERMOSPHERE - The temperature begins to increase with altitude, and this trend continues throughout 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. Because of the great spacing between molecules, the
thermosphere has high temperatures, but very low heat.
The space shuttles, satellites, and space station all fly within the thermosphere. They are required to stay within this boundary
to ensure that they remain captured by Earth’s gravity and stay in orbit around the Earth. The Earth’s magnetic field also
extends and protects the Earth from solar wind. When this occurs it causes a natural wonder, the Aurora Borealis (a.k.a.
northern lights).
Above the thermosphere is an area where the atmosphere meets space, and where the Earth’s gravity can no longer firmly hold
molecules with gravity. This area, where molecules escape, is called the exosphere.
