Content Benchmark E.8.A.4
Students understand the composition of Earth’s atmosphere, emphasizing the role of the
atmosphere in Earth’s weather and climate. I/S
Life on Earth is supported by the atmosphere, solar energy, and our planet's magnetic fields. The
atmosphere absorbs the energy from the Sun, recycles water and other chemicals, to provide a
moderate climate. The atmosphere also protects us from high-energy radiation and the frigid
vacuum of space. Earth’s atmosphere is a very thin layer of gases that surround a very large
planet. An analogy of the relative diameter of the Earth compared to the thickness of the
atmosphere would be to exhale onto a billiard ball (from a pool table). The billiard ball
represents the Earth and the thin layer of condensation represents the relative thickness of its
atmosphere.
The atmosphere makes up less than one millionth of the total mass of the Earth but is critical to
life. Two gases make up the bulk of the atmosphere: nitrogen (N2) at 78% and oxygen (O2) at
21%, as indicated in Figure 1. The other one percent includes water vapor, carbon dioxide (CO2),
argon, and trace amounts of other gases.
Constant components
(proportions remain the same over time and location)
Nitrogen (N2)
78.08%
Oxygen (O2)
20.95%
Argon (Ar)
0.93%
Neon, Helium, Krypton
0.0001%
Variable components
(amounts vary over time and location)
Carbon dioxide (CO2)
0.038%
Water vapor (H20)
0-4%
Methane (CH4)
trace
Sulfur dioxide (SO2)
trace
Ozone (O3)
trace
Nitrogen oxides (NO, NO2)
trace
Figure 1. Average Chemical Composition of Earth’s Atmosphere.
(From http://www.visionlearning.com/library/module_viewer.php?mid=107)
Although both nitrogen and oxygen are essential to life on the planet, they have little effect on
weather and other atmospheric processes. The variable components, which make up far less than
1% of the atmosphere, have a much greater influence on both short-term weather and long-term
climate. For example, variations in water vapor impact relative humidity. Along with water
vapor, CO2, CH4, N2O, and SO2 all have an important property: they absorb heat emitted by the
Earth and thus warm the atmosphere, creating what we call the greenhouse effect. This topic is
elaborated upon later in this section.
In addition to gases, the atmosphere also contains particulate matter such as dust, volcanic ash,
rain, snow, and ice crystals. These are highly variable and are generally less persistent than gas
concentrations, but they can sometimes remain in the atmosphere for relatively long periods of
time.
Layers of the Atmosphere
Based on thermal properties (temperature trends), chemical composition, movement, and density
Earth’s atmosphere is divided into four layers; troposphere, stratosphere, mesosphere, and
thermosphere (Figure 2).
Figure 2. Temperature trends and layers of Earth’s atmosphere.
(From http://www.physicalgeography.net/fundamentals/7b.html)
Troposphere
Beginning at Earth’s surface and extending upward to a height of somewhere between 8-16
kilometers (~5 to 10 miles), the troposphere is where almost all the weather takes place – clouds
form and precipitation falls, wind blows, humidity varies, and the atmosphere interacts with the
Earth below. The depth of this layer varies greatly from place to place and is influenced by
unequal heating and energy transfer between Earth’s surface and the atmosphere via conduction,
convection, and radiation. Its depth is greatest at the tropics where warm temperatures cause
vertical expansion of the lower atmosphere. This layer decreases to a minimum depth in the polar
region. The average depth of the troposphere is 11 kilometers, as indicated in Figure 2.
Temperature decreases with height (altitude) in the troposphere at an approximate rate of 6.5
degrees Celsius for every vertical kilometer traveled (known as the environmental lapse rate). As
you climb higher, the temperature drops from an average of about 17°C (62°F) at Earth’s surface
to -51°C (-60°F) near the top of the troposphere.
For further information on the troposphere and other atmospheric layers, visit
http://www.enviroliteracy.org/category.php/1.html
Stratosphere
The stratosphere extends from the top of the troposphere (tropopause) to an altitude of 50
kilometers (~30 miles). The temperature trend within this layer is reversed from what is observed
in the troposphere. In the stratosphere, as altitude increases temperature increases. The higher
temperatures found in this layer occurs because of a localized concentration of ozone gas
molecules (O3). These molecules absorb ultraviolet (UV) radiation generating thermal energy
that warms the stratosphere. Ozone is primarily found in the atmosphere at varying
concentrations between the altitudes of 10 to 50 kilometers. This layer of ozone is also called the
ozone layer. The ozone layer is important to organisms at the Earth's surface as it protects them
from the harmful effects of the Sun's ultraviolet (UV) radiation by absorbing it before it reaches
the Earth’s surface. Without the ozone layer life could not exist on the Earth's surface.
To learn more about stratospheric ozone and the ozone layer, go to
http://www.nas.nasa.gov/About/Education/Ozone/ozone.html
Mesosphere
The mesosphere (literally “middle sphere”) is the third highest layer of Earth’s atmosphere,
spanning the region from 50 kilometers to 80 kilometers above the surface. The gases continue to
become thinner and thinner (in other words, less dense) with height. However, the gases in the
mesosphere are concentrated enough to slow down meteorites plunging toward Earth’s surface.
Here is where most meteorites (shooting stars) burn up, leaving a fiery trail in the night sky. The
temperature trend in this layer is reversed from what was seen in the stratosphere. Temperature
decreases as altitude increases in the mesosphere. In fact, this is the coldest layer of Earth’s
atmosphere where temperatures are colder than Antarctic’s lowest recorded temperature!
Thermosphere
The thermosphere extends from the top of the mesosphere (the mesopause, at 80 kilometers) to
an altitude of approximately 600 kilometers (375 miles). The temperature trend here is similar to
what is observed in the stratosphere – as altitude increases, temperature increases. This is the
hottest layer of our atmosphere which occurs due to the absorption of intense solar radiation by
the limited amount of remaining atmospheric gases. However, in spite of the high temperature,
this layer of the atmosphere would still feel very cold to our skin because of the extremely thin
air (very low density of gas). The total amount of energy from the very few molecules in this
layer is not adequate enough to heat our skin.
Pressure and the Atmosphere
Atmospheric pressure can be imagined as the weight of the overlying column of air. Unlike
temperature, pressure decreases exponentially with altitude. Traces of the atmosphere can be
detected as far as 500 km above the surface of the earth, but 80 percent of the atmosphere’s mass
is contained within the 18 km closest to the surface. Atmospheric pressure is generally measured
in millibars (mb); this unit of measurement is equivalent to 1 gram per centimeter squared (1
g/cm2). Other units are occasionally used, such as kilopascals, atmospheres, or millimeters of
mercury (see http://www.srh.noaa.gov/elp/wxcalc/pressureconvert.shtml for a Pressure Unit
Conversion Calculator).
At sea level, pressure ranges from about 960 to 1,050 mb, with an average of 1,013 mb. Fifty
percent (50%) of all the molecules that make-up the atmosphere lie within the first 5.5 kilometers
(18,000 feet) of Earth’s surface, and 99% lies within 30 kilometers of the ground. At the top of
Mt. Everest (elevation 8,848 meters or 29,028 feet), pressure is as low as 300 mb. Because gas
pressure is related to density, this low pressure means that there are approximately one-third as
many gas molecules inhaled per breath on top of Mt. Everest as at sea level – which is why
climbers experience ever more severe shortness of breath the higher they go, as less oxygen is
inhaled with every breath.
Figure 3. Pressure and layers of atmosphere
(From http://www.physicalgeography.net/fundamentals/images/pressure_altitude.jpg)
For additional information related to Earth’s atmosphere visit
http://www.visionlearning.org/library/module_viewer.php?c3=1&l=3&mid=107
and, http://www.srh.noaa.gov/jetstream/atmos/layers.htm
An animated diagram that allows you to investigate the height, temperature, pressure,
composition, and layers of the atmosphere can be accessed at,
http://earthguide.ucsd.edu/earthguide/diagrams/atmosphere/index.html
Atmospheric Gases and the Greenhouse Effect
In the atmospheric greenhouse effect, the type of surface that sunlight first encounters is the most
important factor. Forests, grasslands, ocean surfaces, ice caps, deserts, and cities all absorb,
reflect, and radiate radiation differently. Sunlight falling on a white glacier surface strongly
reflects back into space, resulting in minimal heating of the surface and lower atmosphere.
Sunlight falling on a dark desert soil is strongly absorbed, on the other hand, and contributes to
significant heating of the surface and lower atmosphere. Cloud cover also affects greenhouse
warming by both reducing the amount of solar radiation reaching the Earth's surface and by
reducing the amount of radiation energy emitted into space.
For more information on the Greenhouse Effect, visit http://www.ucar.edu/learn/1_3_1.htm
Like the greenhouse covering, our atmosphere also serves to retain heat at the surface of the
Earth. Much of the sun's energy reaches Earth as visible light. Of the visible light that enters the
atmosphere, about 30% is reflected back out into space by clouds, snow and ice-covered land,
water surfaces, and atmospheric dust. The rest is absorbed by the liquids, solids, and gases that
constitute our planet. The energy absorbed is eventually reemitted, but not as visible light.
Instead, it's emitted as longer-wavelength light called infrared radiation. This is also called "heat"
radiation, because although we cannot see in infrared, we can feel its presence as heat. This is
what you feel when you put your hand near the surface of a hot skillet. Certain gases in our
atmosphere (known as "trace" gases because they make up only a tiny fraction of the
atmosphere) can absorb this outgoing infrared radiation, in effect trapping the heat energy. This
trapped heat energy makes the Earth warmer than it would be without these trace gases.
The ability of certain trace gases to be relatively transparent to incoming visible light from the
sun yet opaque to the energy radiated from Earth is one of the best-understood processes in
atmospheric science. This phenomenon has been called the "greenhouse effect" because the trace
gases trap heat similar to the way that a greenhouse's transparent covering allows light to pass
into the green house but traps heat by not letting it pass out of the greenhouse. Without our
atmospheric greenhouse effect, Earth's surface temperature would be far below freezing. On the
other hand, an increase in atmospheric trace gases could result in increased trapped heat and
rising global temperatures. The greenhouse effect is defined as the process which causes the
surface of the Earth to be warmer than it would have been in the absence of an atmosphere. If
Earth’s atmosphere were removed, average temperatures would be about 30°C (50°F) lower than
present.
Visit “What is a greenhouse?” for further information http://www.ucar.edu/learn/1_3_2_12t.htm
Figure 4. The Greenhouse Effect.
(From http://www.ucar.edu/learn/1_3_2_12t.htm)
Carbon dioxide (CO2), water vapor (H2O), methane (CH4), nitrous oxide (N2O), and a few other
gases are greenhouse gases. They all are molecules composed of more than two component
atoms, bound loosely enough together to be able to vibrate with the absorption of heat. The
major components of the atmosphere (N2 and O2) are two-atom molecules too tightly bound
together to vibrate and thus they do not absorb heat and contribute to the greenhouse effect.
For greater detail on Earth’s greenhouse gases, their source, and function in the atmosphere see
http://www.enviroliteracy.org/article.php/428.html
Greenhouse effect background information and links to classroom-ready activities can be found
at http://www.enviroliteracy.org/article.php/367.html
For an animated simulation of the Greenhouse Effect, go to
http://earthguide.ucsd.edu/earthguide/diagrams/greenhouse/
and, http://www.epa.gov/climatechange/kids/global_warming_version2.html
Content Benchmark E.8.A.4
Students understand the composition of Earth’s atmosphere, emphasizing the role of the
atmosphere in Earth’s weather and climate. I/S
Common misconceptions associated with this benchmark.
1. Students incorrectly believe that air is not the same everywhere and that Earth’s
atmosphere extends far into space.
Earth’s atmosphere is a very thin layer wrapped around a very large planet. An analogy of
the relative diameter of the Earth compared to the thickness of the atmosphere would be to
exhale onto a billiard ball (from a pool table). The billiard ball represents the Earth and the
thin layer of condensation represents the relative thickness of its atmosphere. The actual
thickness of Earth’s atmosphere is approximately 550 kilometers (350 miles), but over 99%
of all gas molecules are found within the first 30 miles from the planet’s surface! Air is
composed of several gases and varies in relative abundance from place to place. However,
two gases make up a bulk of the Earth’s atmosphere; nitrogen (~78%) and oxygen (~21%),
with much smaller amounts of water vapor, carbon dioxide (CO2), and others.
To learn more about this misconception visit
http://www.csulb.edu/~lhenriqu/NARST2000.htm
2. Students inaccurately think gases make things lighter.
Gas has mass. Gas is a phase of matter and therefore has mass and takes up space. How much
something weighs depends upon how much and what kind of matter is present. Density of the
material also matters. Having gas inside something does not make it lighter – although it can
change its density. A possible source of this misconception is gases that students have
experience with (balloons – air or helium) tend to be light. Many things that float have gas or
air trapped in them (a large ship) – rather than focusing on the density of the object, which
changes when the volume changes, students often focus on the air trapped inside.
Additional information related to this and other Atmosphere and Gases misconceptions visit
http://www.csulb.edu/~lhenriqu/NARST2000.htm
3. Students incorrectly think that the greenhouse effect is caused when gases in the
atmosphere behave as a blanket and trap radiation which is reradiated to the Earth.
To begin with; the greenhouse effect and global warming is not the same thing. There is a
greenhouse effect, which to a point is a very good thing for life on our planet; as without it
the temperatures would be too cold and life could not exist (as we know it). The greenhouse
effect is defined as the process which causes the surface of the Earth to be warmer than it
would have been in the absence of an atmosphere. If Earth’s atmosphere were removed,
average temperatures would be about 30°C (50°F) lower than present. Conversely, global
warming is the term given to an expected increase in the magnitude of the greenhouse effect,
whereby the surface of the Earth will almost inevitably become hotter than it is now – and
occur because of the action of humans.
Our atmosphere has a profound effect on Earth’s surface temperature as seen above. The best
explanation to provide students is “the surface of the Earth is warmer than it would be in the
absence of an atmosphere because it receives energy from two sources: the sun and the
atmosphere”.
For a complete discussion on this misconception visit
http://www.ems.psu.edu/~fraser/Bad/BadGreenhouse.html
Content Benchmark E.8.A.4
Students understand the composition of Earth’s atmosphere, emphasizing the role of the
atmosphere in Earth’s weather and climate. I/S
Sample Test Questions
1. The two most abundant gases in Earth’s atmosphere are
a. Nitrogen and carbon dioxide
b. Oxygen and water vapor
c. Carbon dioxide and water vapor
d. Nitrogen and oxygen
2. In which layer do virtually all weather phenomena take place?
a. Troposphere
b. Stratosphere
c. Mesosphere
d. Thermosphere
3. Which pie graph best represents the percentage of gases in the troposphere?
4. The layers of the atmosphere are defined by
a. Altitude
b. Temperature
c. Gaseous composition
d. Air pressure
5. The most abundant gas in Earth’s atmosphere is
a. Carbon Dioxide
b. Oxygen
c. Nitrogen
d. Ozone
6. Which statement most accurately describes the Earth’s atmosphere?
a. The atmosphere is layered, with each layer possessing distinct characteristics.
b. The atmosphere is a shell of gases surrounding most of the Earth.
c. The atmosphere’s altitude is less than the depth of the ocean.
d. The atmosphere is more dense than the hydrosphere but less dense than the lithosphere.
7. Which gas in the atmosphere protects life by absorbing ultraviolet (UV) rays of the sun?
a. Nitrogen
b. Oxygen
c. Carbon Dioxide
d. Ozone
8. Carbon dioxide (CO2) in the atmosphere is most important as a
a. Filter for ultraviolet radiation
b. Heat absorber
c. Reflector of sunlight
d. Shield for meteors
9. Which statement most accurately describes the temperature trend in the troposphere?
a. Temperatures rise with increasing altitude above the Earth.
b. Temperatures rise then fall with increasing altitude above the Earth.
c. Temperatures decrease with increasing altitude above the Earth.
d. Temperatures remain constant with increasing altitude above the Earth.
10. Ozone is concentrated in Earth’s atmosphere at an altitude of 20 to 35 kilometers. Which
atmospheric layer contains the greatest concentration of ozone?
a. Thermosphere
b. Mesosphere
c. Stratosphere
d. Troposphere
11. As the altitude increases within Earth’s troposphere, air temperature generally
a. Decreases, only
b. Increases, only
c. Decreases, then increases
d. Increases, then decreases
12. The graph below shows the change in carbon dioxide concentration in parts per million
(ppm) in Earth’s atmosphere from 1960 to 1990.
The most likely cause of the overall change in the level of
carbon dioxide from 1960 to 1990 is an increase in the
a.
b.
c.
d.
number of violent storms
number of volcanic eruptions
use of nuclear power
use of fossil fuels
Content Benchmark E.8.A.4
Students understand the composition of Earth’s atmosphere, emphasizing the role of the
atmosphere in Earth’s weather and climate. I/S
Answers to Sample Test Questions
1. (d)
2. (a)
3. (a)
4. (b)
5. (c)
6. (a)
7. (d)
8. (b)
9. (c)
10. (c)
11. (a)
12. (d)
Content Benchmark E.8.A.4
Students understand the composition of Earth’s atmosphere, emphasizing the role of the
atmosphere in Earth’s weather and climate. I/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. Introduction to the Atmosphere Activities
Sponsored by the National Science Foundation (NSF) and University Corporation for
Atmospheric Research (UCAR), this on-line teaching module is targeted for middle school
science teachers. The site provides background information and supporting classroom
teaching materials. The content focus is climate change and issues related to both
stratospheric and tropospheric ozone.
The Goldilocks Principle: A Model of Atmospheric Gases
Teacher’s guide to what atmospheric scientists call The Goldilocks Principle: "Venus is too
hot, Mars is too cold, but Earth is just right!" Students will use similarities and differences in
the atmospheres of these planets to develop an appreciation and importance of the
greenhouse effect on Earth. A link to the student guide is contained within the top menu bar.
To access this activity, visit: http://www.ucar.edu/learn/1_1_2_1t.htm
How High Does the Atmosphere Go?
This two-part activity demonstrates the relative thickness of the thin layer that includes the
troposphere and stratosphere. Students will be able to explain how relatively thin the
atmosphere is, compared to the size of the planet and will understand the relative extent of
the four major atmospheric layers. A link to the student guide is contained within the top
menu bar.
To access this activity, visit: http://www.ucar.edu/learn/1_1_2_2t.htm
What is a Greenhouse? and What Factors Impact a Greenhouse?
These activities are designed to have students become familiar with how a greenhouse retains
heat by building simple models and then exploring several factors that influence the amount
of heating and cooling. A link to the student guide is contained within the top menu bar.
To access this activity, visit: http://www.ucar.edu/learn/1_3_2.htm
What Do Concentrations Mean? Comparing Concentrations of Gases in our Atmosphere
In this activity, students will use a dilution experiment to understand the concept of part-permillion (ppm) and part-per-billion (ppb) measurements. Through discussion, they will be
able to relate these dilutions to concentrations of gases in our atmosphere.
To access this activity, visit: http://www.ucar.edu/learn/1_4_2_14t.htm
2. Atmosphere Lessons by Astrophysics Science Project Integrating Research &
Education (ASPIRE)
What is this atmosphere that surrounds the Earth? This instructional tutorial, part of an
interactive laboratory series, introduces students to the structure, effects, and components of
the atmosphere. Here students investigate the composition of the atmosphere; effects of
temperature, pressure, and ozone; the greenhouse effect; and how Earth compares with other
planets. Interactive activities present students with opportunities to explore ideas and answer
questions about the atmosphere, including its structure, the making of ozone, rocket
launching, and measuring the atmosphere. Pop-up boxes provide additional information on
topics such as dust, rain, and atmospheric composition.
Atmosphere homepage of modules is located at
http://sunshine.chpc.utah.edu/labs/atmosphere/atmosphere_main.html
Measuring the Atmosphere: Temperature, Pressure, and Ozone
In this activity you have the opportunity to ride a balloon operated by the premier hot air
balloon company of the West! Today you’ve been invited to come on board with a bunch of
scientists who are studying the Earth’s atmosphere. It’s not the same at different altitudes you
know! You have been assigned a job by the head scientist: Measure temperature and pressure
readings as the hot air balloon rises. This lesson has three main objectives; 1) Determine the
relationship between atmospheric pressure and altitude. 2) Determine the relationship
between temperature and altitude. 3) Determine the location of ozone in the Earth’s
atmosphere.
Access this activity at
http://sunshine.chpc.utah.edu/labs/atmosphere/atm_measure2.html
3. Weather Scope by the Center for Innovation in Engineering and Science Education
(CIESE)
Weather Scope: An Investigative Study of Weather and Climate is an Internet-based
multidisciplinary project which will enrich a student's learning experience through "unique
and compelling" applications of instructional technology. This project is broken up into five
(5) core lessons and additional supplementary and enrichment activities. These core lessons
are; 1) Make a weather station 2) Using the internet to observe weather 3) Track weather
like a meteorologist 4) How does the weather change? 5) Are weather forecasts always
right?
To access the entire Weather Scope project including teacher guides and student activities,
visit http://www.ciese.org/curriculum/weatherproj2/en/guidelessons.shtml.
4. The Ozone Hole Tour
This resource was created by the Centre for Atmospheric Science from the University of
Cambridge, UK. The Ozone Hole Tour is a multimedia overview of the current scientific
understanding of the dynamics of the hole in the ozone layer. There are four components to
this tour; 1) The discovery of the ozone hole, 2) Recent ozone loss over Antarctica, 3) The
science of the ozone hole, 4) Latest ozone hole research at Cambridge.
To access this resource, go to
http://www.atm.ch.cam.ac.uk/tour/
5. Earth’s Atmosphere: Composition and Structure Article from Vision Learning
This 5 page article provides a review of Earth’s atmospheric composition including both
constant and variable components. Instruments and techniques for measuring atmospheric
variables are explored including temperature and pressure trends. Several related modules
and external resources are provided at the end of the article along with links for further
exploration.
To access this article and supplementary resources, visit
http://www.visionlearning.com/library/module_viewer.php?mid=107
6. Fundamentals of Physical Geography Chapter 7: Introduction to the Atmosphere
The Fundamentals of Physical Geography (2nd Edition) online textbook describes an area of
knowledge within Geography known as Physical Geography created by Dr. Michael
Pidwirny at the University of British Columbia Okanagan. The Fundamentals of Physical
Geography online textbook contains over three hundred pages of information and more than
four hundred 2-D illustrations, photographs, and animated graphics organized into ten
chapters. Important key terms in the text are linked to an interactive glossary of terms.
Nested within the pages of this online textbook are links to study guide pages and additional
reading pages for each chapter. Chapter 7 focuses on Earth’s atmosphere, composition and
layers, greenhouse effect and global warming, and many other topics related to Earth’s
weather and climate.
To explore this resource, go to http://www.physicalgeography.net/weblinks_ch7.html
7. Encyclopedia of the Atmospheric Environment, part of the Awesome Library
Information from this Encyclopedia focuses on nine core topic areas; Acid Rain, Air Quality,
Global Warming and Ozone Depletion study the impact of mankind's pollution on the
atmosphere. The Atmosphere, The Weather and The Climate investigate some of the basic
physical and chemical processes which take place in the atmosphere. Climate Change looks
further at natural influences on the global climate beyond man-made global warming.
Finally, Sustainability is concerned with some of the solutions mankind is adopting to reduce
environmental pollution, in particular the pollution of the atmosphere.
To survey this resource, visit http://www.ace.mmu.ac.uk/eae/english.html