What is the basis for dividing the atmosphere into four layers?
The layer of gases that surrounds Earth is called the atmosphere. The atmosphere is
made up of air, a mixture of chemical elements and compounds. The atmosphere
protects Earth’s surface from the sun’s radiation, helps regulate the temperature of
Earth’s surface, and redistributes the energy absorbed from the sun.
The atmosphere is constantly changing. Weather systems form, move across Earth’s
surface, and dissipate. Weather systems do not move randomly but follow patterns.
Although such patterns can make the weather predictable, there is still much that we
do not know about this important sphere of Earth.
Explain From the ISS view, the atmosphere appears to be made of several
layers. Why do you think the atmosphere has different layers? What roles might
each layer have?
9.1
The Atmosphere
Gather Evidence
Record observations about
Earth’s atmosphere, the layers of
the atmosphere, and what occurs in
each. As you explore the lesson,
gather evidence to help explain the
structure of the atmosphere, what
occurs in each layer and how the
atmosphere interacts with other
earth spheres.
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How do scientists gather information about the structure of Earth’s atmosphere? One
way of doing this involves attaching instruments to a weather balloon. As the balloon
rises, onboard instruments take various measurements at different altitudes, such
as gas compositions, temperatures, pressures, and wind directions. The instrument
package relays the information to the ground by radio.
Composition of the Atmosphere
Air is composed of different gases. These gases include elements and compounds.
Air is mainly composed of the elements nitrogen, oxygen, and argon. The two most
abundant compounds in air are the gases water vapor, H
2
O, and carbon dioxide,
CO
2
. In addition to containing gaseous elements and compounds, the atmosphere
commonly carries various kinds of tiny solid particles called particulates. Particulates in
the atmosphere can include dust, pollen, and pollution, such as smoke.
FIGURE 3: The atmosphere is constantly interacting with Earth’s other spheres. a Plant photosynthesis and respiration b Animal respiration c Clouds d An industrial smokestack
Predict What elements and compounds make up the gases in the atmosphere?
Predict Atmospheric
scientists use weather
balloons to take measurements
continuously as they rise through
the atmosphere. However, weather
balloons are only useful up to an
altitude of about 40 km. Above this
altitude, the balloons break. Why
do you think this happens?
FIGURE 2: As a weather balloon
rises, its instruments gather
important data about the
atmosphere.
Lesson 1 The Atmosphere 495
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FIGURE 4: Composition of Earth’s atmosphere
(dry air, excludes water vapor)
78%
21%
1% >1%
Nitrogen
Oxygen
Argon
Other
78%
21%
1% >1%
Nitrogen
Oxygen
Argon
Other
78%
21%
1% >1%
Nitrogen
Oxygen
Argon
Other
Levels in the Atmosphere
FIGURE 5: Graph of altitude versus temperature for Earth’s
atmosphere
Temperature Trends In
Figure 5, does the temperature
stay the same at all altitudes? Are
there specific altitudes where the
changes in temperature trends
occur? In your Evidence Notebook,
copy this graph and draw horizontal
lines where the temperature
changes occur.
Hands-On Activity
Gases in the atmosphere can cycle
from the atmosphere to other Earth
spheres (hydrosphere, biosphere,
lithosphere, etc.). For example, the
process of photosynthesis cycles
oxygen, carbon dioxide, and water
vapor between the biosphere and
the atmosphere. Similarly, certain
bacteria absorb nitrogen from the
atmosphere while others release it.
Water vapor enters the atmosphere
when water evaporates and returns
to Earth’s surface as it condenses and
falls as precipitation.
These cycles can cause the
concentrations of some gases
to fluctuate. For example, in arid
environments, the concentration
of water vapor in the air can be less
than 1%, while in wet climates, it can
be as high as 4%.
Atmospheric scientists have studied the composition of Earth’s atmosphere with
weather balloons, sounding rockets, aircraft, and spacecraft. Their data indicate that
the composition of dry air is nearly the same everywhere on Earth’s surface up to an
altitude of about 80 km.
Explain How do local fluctuations in the gas composition of the atmosphere relate to
biogeochemical cycles that you have learned?
Layers of the Atmosphere
Is the atmosphere the same at all altitudes? When traveling
up a mountain road to a high altitude, you may have noticed
that your ears “pop” somewhere along the way. Perhaps you
noticed that at higher altitudes, it is often colder than near sea
level. These observations indicate that the atmosphere is not
the same at all altitudes.
Because of the force of gravity, the air molecules are compressed
together and exert a force on everything near Earth’s surface.
The pressure exerted on a surface by the atmosphere is called
atmospheric pressure. Atmospheric pressure is exerted equally
in all directions—up, down, and sideways. Earth’s gravity
keeps 99% of the total mass of the atmosphere within 32
km of Earth’s surface. The remaining 1% extends upward for
hundreds of kilometers but gets increasingly thinner at high
altitudes. Because there is less weight pressing down from
above at higher altitudes, the air molecules are farther apart and
exert less pressure on each other. Thus, atmospheric pressure
decreases as altitude increases.
496 Unit 9 The Atmosphere
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The Troposphere
Earth’s atmosphere has a distinctive pattern of temperature changes that occur with
increasing altitude, The temperature differences mainly result from how solar energy
is absorbed as it moves through the atmosphere. Scientists identify four main layers of
the atmosphere based on these differences.
The atmospheric layer that is closest to Earth’s surface is called the troposphere.
Almost all the water vapor in the atmosphere is found in this layer where nearly all
weather occurs. Most sunlight passes through the atmosphere and warms Earth’s
surface, which in turn heats the lower part of the troposphere by evaporation, thermal
radiation, and conduction. The combination of these factors creates a heat gradient
in which temperature decreases as altitude increases. The temperature decreases at
an average rate of 6.5 °C per kilometer from Earth’s surface. However, at an average
altitude of 12 km, the temperature stops decreasing. This zone is called the tropopause
and represents the upper boundary of the troposphere. The altitude of the tropopause
varies with latitude and season.
The Stratosphere
The layer of the atmosphere called the stratosphere extends from the tropopause to
an altitude of nearly 50 km. Almost all the ozone in the atmosphere is concentrated
in this layer. In the lower stratosphere, the temperature is almost –60 °C. In the upper
stratosphere, the temperature increases with altitude because air in the stratosphere
is heated as ozone absorbs solar radiation. The temperature of the air rises steadily to
a temperature of about 0 °C at an altitude of about 50 km above Earth’s surface. This
zone, called the stratopause, marks the upper boundary of the stratosphere.
The Mesosphere
Located above the stratopause is
the mesosphere where temperature
decreases as altitude increases. The
mesosphere extends to roughly 80 km,
though the exact altitude changes with
the seasons. The upper boundary of the
mesosphere is called the mesopause. It
has an average temperature of nearly
–90 °C, which is the coldest temperature
in the atmosphere. Above this
boundary, temperatures again begin to
increase.
In the mesosphere, atmospheric
pressure becomes so low that weather
balloons expand to many times their
original size before rupturing.
Temperature Change with Altitude
FIGURE 6: Trends in temperature change reverse at the various pauses of Earth’s
atmosphere.
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The Thermosphere
The atmospheric layer above the mesopause is called the thermosphere. In the
thermosphere, temperature increases steadily as altitude increases because nitrogen
and oxygen atoms absorb solar radiation. Because air particles in the thermosphere are
very far apart, they do not strike a thermometer often enough to produce an accurate
temperature reading. Therefore, special instruments are needed. These instruments
have recorded temperatures of more than 1000 °C in the thermosphere.
The lower region of the thermosphere, at an altitude
of 80 to 400 km, is commonly called the ionosphere.
In the ionosphere, solar radiation that is absorbed by
atmospheric gases causes the atoms of gas molecules
to lose electrons and to produce ions and free electrons.
Interactions between solar radiation and the ionosphere
cause the phenomena known as auroras. The upper limit
of the thermosphere varies through time from 500 km to
1000 km. However, above the thermosphere is the region
where Earth’s atmosphere blends into the almost complete
vacuum of space. This zone of indefinite altitude, called
the exosphere, extends for thousands of kilometers above
the ionosphere. The exosphere is rich in hydrogen and
helium gases, which are light enough to escape Earth’s
gravity into outer space.
3 answers
The division of Earth's atmosphere into layers is based primarily on temperature gradients, composition, and the behavior of the gases within each layer. Here’s a more detailed exploration of the four main layers of the atmosphere—troposphere, stratosphere, mesosphere, and thermosphere—and their roles:
1. Troposphere
Altitude Range: From the Earth's surface up to about 8-15 km, depending on the latitude and season.
Characteristics:
Contains nearly all of the atmosphere's water vapor and is where most weather events occur (clouds, rain, storms).
Temperature decreases with altitude; on average, it decreases by about 6.5 °C for every kilometer gained in altitude. This is due to the fact that the Earth's surface absorbs solar radiation and warms the air closest to it.
The boundary at the upper limit is called the tropopause, which marks the transition to the next layer.
Role: The troposphere provides the necessary conditions for life on Earth and is crucial for weather and climate.
2. Stratosphere
Altitude Range: From the tropopause (about 12 km) to about 50 km above the Earth.
Characteristics:
Contains the ozone layer, which absorbs and scatters ultraviolet solar radiation, protecting living organisms from harmful UV rays.
Temperature increases with altitude in this layer because ozone absorbs UV radiation and heats the surrounding air.
The upper boundary is called the stratopause.
Role: The stratosphere protects life on Earth by filtering harmful UV radiation and is stable, making it a key area for commercial aviation and weather monitoring.
3. Mesosphere
Altitude Range: Extends from the stratopause (about 50 km) to approximately 80 km.
Characteristics:
Temperature decreases with altitude, reaching the coldest temperatures in the atmosphere (around -90 °C at the mesopause, the upper boundary of this layer).
This layer is where most meteors burn up upon entering Earth's atmosphere.
Role: The mesosphere plays a role in meteor observation and in protecting Earth from meteoroids.
4. Thermosphere
Altitude Range: From the mesopause (about 80 km) to between 500 km and 1000 km.
Characteristics:
Temperature increases significantly with altitude, with temperatures reaching well over 1000 °C; however, due to the very low density of air, it wouldn't feel hot to humans.
This layer contains the ionosphere, where solar radiation ionizes atmospheric gases, leading to the formation of ions and free electrons, which are important for radio communication.
The thermosphere experiences phenomena like auroras due to interactions between solar particles and atmospheric gases.
Role: The thermosphere is critical for communication technologies and protects the Earth from solar radiation.
Conclusion
The atmosphere has different layers due to varying temperature gradients, which affect gas composition, pressure, and the behavior of atmospheric phenomena. Each layer serves distinct roles that protect life on Earth, facilitate weather patterns, and moderate the planet's climate. The changes in temperature, pressure, and density across these layers influence everything from weather to human activities, showcasing the complex and dynamic nature of Earth's atmosphere.
Interaction with Other Earth Spheres
The atmosphere interacts with other Earth spheres (biosphere, geosphere, hydrosphere) through various biogeochemical cycles. For example, organisms in the biosphere exchange gases with the atmosphere (like CO2 and O2), while the hydrosphere plays a significant role in weather and climate through evaporation and precipitation processes, impacting both ecosystems and the lithosphere. Understanding these interactions contributes to our knowledge of environmental science and climate change.
What causes the temperature to increase with height through the stratosphere?
The increase in temperature with height in the stratosphere is primarily caused by the presence of the ozone layer. Here's a detailed explanation of this phenomenon:
Ozone Layer and Absorption of Solar Radiation
Ozone Layer: The stratosphere contains a high concentration of ozone (O₃) molecules, particularly in a region known as the ozone layer, which is located approximately between 15 and 35 kilometers above the Earth's surface.
Absorption of UV Radiation: Ozone molecules absorb a significant portion of the sun's ultraviolet (UV) radiation, specifically shortwave UV-C and UV-B rays. This absorption of solar radiation occurs primarily in the lower and middle parts of the stratosphere.
Heating Effect: When ozone absorbs UV radiation, it converts that energy into heat, thereby raising the temperature of the air in this layer. As a result, the temperature in the stratosphere increases with altitude, unlike in the troposphere where temperature decreases with height.
Thermal Structure of the Stratosphere
Temperature Gradient: In the lower stratosphere, temperatures can be as low as -60 °C, but as one moves upward toward the stratopause (the upper boundary of the stratosphere), the temperatures gradually rise to around 0 °C. This creates a positive temperature gradient in this layer.
Stability of the Stratosphere: The warming effect of ozone leads to a more stable atmosphere in the stratosphere compared to the troposphere. In stable conditions, vertical mixing is limited, allowing the warmer air above to restrict the cooler air below, which is why weather occurs primarily in the lower troposphere.
Summary
In summary, the increase in temperature with height in the stratosphere is primarily due to the absorption of UV radiation by ozone molecules. This absorption process converts solar energy into heat, resulting in a temperature inversion where the temperature rises with altitude, contrasting with the temperature behavior observed in the troposphere below. This structure of the stratosphere plays a crucial role in protecting Earth's surface from harmful UV radiation and influencing weather and climate patterns.
1 answer