The Earth SystemEarth is the third planet from the sun in our so.docx

The Earth System
Earth is the third planet from the sun in our solar system. Earth
orbits the sun in an elliptical (oval) path. Earth’s orbit is
sometimes called the “Goldilocks zone.” Mercury and Venus
travel too close to the sun to sustain life—they’re “too hot.”
Planets beyond Earth travel too far from the sun—they’re “too
cold.” But Earth is “just right.” (Note that there’s evidence that
Mars—the Red Planet—once may have sustained microscopic
life on its surface. However, conditions on the Red Planet no
longer seem favorable.)
The term “Earth system” refers to the different processes and
cycles that exist on the planet. All of these work together to
sustain life. The four domains of the Earth system include the
geosphere, the hydrosphere, the atmosphere, and the biosphere.
Let’s quickly review each of these.
Layers of Earth
(NASA public domain image)
The geosphere refers to the solid portion of the planet. It
includes the rocks and minerals that make up the continents as
well as the ocean floor. It also includes structures within Earth,
including the liquid mantle and the dense, solid, metallic core.
Nonliving surface ground layers, such as desert sands and
volcanic rock, are part of the geosphere.
The hydrosphere includes all the water on or near Earth’s
surface. The oceans are the major component of the
hydrosphere. They make up 97 percent of the Earth’s water.
Glaciers and polar ice caps make up about 2 percent of the
hydrosphere. Only about 1 percent of the hydrosphere is made
up of the liquid freshwater found in ponds, streams, rivers,
lakes, and underground water reservoirs (aquifers).
Aquifers are the main freshwater source in America’s
“breadbasket” states of the Midwest and Great Plains.
(“Breadbasket” states get their name from the volume of wheat,
a primary ingredient in bread, grown there.) The hydrosphere

extends several miles above the surface of the planet into the
atmosphere, mainly in the form of water vapor.
Water vapor is water in its gaseous state. Precipitation is water
released from the clouds. It may take the form of rain, freezing
rain, sleet, snow, or hail. It’s part of the water cycle.
For more information on the hydrosphere, follow this link: What
is the HYDROSPHERE?
The atmosphere is the planet’s blanket. It allows living beings
on the planet to breathe. It also protects us from the unfriendly
features of the universe, such as meteors, cosmic radiation, and
the effects of solar flares.
The atmosphere is made up of a variety of layers, as follows:
Earth’s Atmosphere
· The troposphere is the densest part of the atmosphere. It starts
at Earth’s surface and extends upward from about 5 miles (in
the higher or lower latitudes) to 9 miles (over the equatorial
regions). Most of our weather takes place here.
· The stratosphere extends from the troposphere upward about
31 miles. The ozone layer, which protects the planet from solar
ultraviolet radiation, is located in this region.
· The mesosphere starts just above the stratosphere. This layer
is where most meteors burn up to become “falling stars.” It
extends upward for about 53 miles.
· The thermosphere extends from just above the mesosphere. It
extends upward for about 372 miles. The thermosphere is the
region where most human-made satellites orbit the planet. It’s
also the location of the Aurora Borealis (the Northern Lights).
· The ionosphere extends upward about 600 miles from the
thermosphere. This layer gets its name because it includes
electrons and assorted ions, allowing for radio communications
on the planet. Broadcast signals are radio frequencies that are
bounced off the ionosphere.
· The exosphere extends from the ionosphere/thermosphere
upward some 6,200 miles. This layer is the outer limit of
Earth’s atmosphere.

For a more in-depth look at the atmosphere, access this site by
NASA: Earth's Atmospheric Layers
The biosphere is the layer of Earth where life exists. It includes
all life on land, water, and in the air. The list of organisms
living on Earth is long and complex. It includes all plants and
fungi. It includes microscopic creatures like bacteria, viruses,
and ocean plankton. And, of course, it includes all animals,
including humans.
Want to review Earth’s system as an animated short? Check out
this video:
Ecology Defined
Ecology is the branch of biology that deals with the
relationships between organisms and their environments.
Ecologists employ scientific methods. They work to understand
how organisms act and interact with the physical and chemical
environment around them.
The term “ecology” also refers to organized efforts to
understand and protect the environment. Ecologists seek to
understand practices that affect the environment, such as timber
clear-cutting and petroleum-based “factory” farming, and
replace them with alternative, sustainable practices.
Basic Concepts of Ecology
Ecosystems
An ecosystem is a biological community of organisms and their
shared environment. Many kinds of ecosystems exist on Earth.
Examples include ponds, grasslands, forests, estuaries (the tidal
mouth of rivers, where tides and streams meet), and marshes
like the Florida Everglades.
In many cases, the actual boundaries of any ecosystem are hard
to determine. Researchers work on defining specific locales. We
do know that an ecosystem is made up of a community of
different living (biotic) flora and fauna that interact with each
other in a specific, nonliving (abiotic) environment. Abiotic
factors include sunlight, the physical and chemical makeup of
the environment, and the local climate pattern.
The main focus of an ecosystem study involves the processes

that link living (biotic) components to nonliving (abiotic)
components through energy transformations and biochemical
cycling. As an example, look at the illustration of the nitrogen
cycle. The nitrogen cycle is the process by which nitrogen gets
from the air into the soil and then into plants and animals.
Eventually it cycles back to the air.
Can you identify the biotic (living) components in the
illustration? These include animals that supply wastes, plants,
and decomposers (mushrooms and fungi that break down dead
or decaying organisms).
The arrows show vital processes of biochemical cycling.
Through these processes, nitrogen from the air is supplied to
plants. Follow the arrows to track the complete cycle of
nitrogen that starts in the atmosphere and returns to it. Energy
transformations occur wherever you see chemical reactions in
the illustration. For example, nitrogen-fixing bacteria provide
nitrogen to the roots of legumes. Decomposers break down the
bodies of dead organisms and return nitrogen to the soil in the
form of ammonia.
The Nitrogen Cycle
(EPA public domain image)
Are you interested in learning more about the nitrogen cycle?
Review this presentation:
Other vital environmental cycles include the water (hydrologic)
cycle, the carbon cycle, and the phosphorus cycle.
As you think about these cycles, keep in mind that ecology is
defined as the interactions of organisms with one another and
with the environment. That can happen in all sorts of ways.
However, an ecosystem is deemed healthy if the interactions
are sustainable; that is, they’re balanced and stable. In a
sustainable ecosystem, the cycles work flawlessly and
dependably. The ecosystem can adapt to changing seasons and
the gradual change of climate patterns.
By contrast, unhealthy ecosystems are unbalanced or unstable.
Ecosystems can become unhealthy in a variety of ways. For
example, petroleum-based mechanized agriculture disrupts

various natural cycles, such as the nitrogen cycle, by depleting
or contaminating the soil.
Within the environment of an ecosystem, a habitat is the actual
location in which organisms like plants and animals live. For
example, the environment around the Mountain Lake Hotel in
Virginia forms a specific habitat. It’s also the location of a
University of Virginia environmental field station. If you scan
the terrain around and beyond a particular kind of habitat such
as Mountain Lake, you can establish its geographic range.
The geographic range includes all the local areas that feature
similar habitats.
Ecological studies may focus on individuals, populations,
communities, and/or entire ecosystems. Sometimes studies focus
on individuals, such as white tail deer, painted turtles, redwing
blackbirds, loblolly pines, or birch trees. These studies examine
reproduction, behavioral development, and physiology. When
the focus is on populations, the study might examine the
species’ resource needs, group behaviors, and population
growth. Ecologists might focus on the sources of a species’
abundance on the one hand as well as conditions that may lead
to its extinction on the other.
Studies of communities look at how the populations of different
species interact with each other. For example, studies may focus
on the interactions between predators and their prey. Predator
and prey populations are interdependent. When predators reduce
the population of a prey below a certain level, predator
populations will also decrease. Other community studies might
examine relationships between competing species that thrive on
the same resources. For example, in Australia, the population of
European feral (wild) rabbits negatively impact native grazing
species like wallabies. In this context, feral rabbits are defined
as an invasive species. Invasive species aren’t native to an
environment and can cause harm.
Sample Food Chain
(EPA public domain image)
The community of organisms and their environments form an

ecosystem. When we study the ecosystem itself, we’re engaged
in ecosystem ecology. That is, we’re looking at how the whole
system works. These types of studies focus on functional
aspects of the system, including the following:
· The amount of energy supplied to the system
through photosynthesis*
· The distribution of energy through the food chain
· The rates of organic decomposition and the rate at which
nutrients are recycled within the system
*Photosynthesis is the process by which phytoplankton and all
the many species of plants absorb energy from the sun and
provide it to all life on Earth. A simplified formula for the
process of photosynthesis looks like this:
6CO2 + 6H2O → (sunlight) → C6H12O6 + 6O2
In the balanced equation, 6 molecules of carbon dioxide + 6
molecules of water = glucose [C6H 12O6] + 6 molecules of
oxygen.
Photosynthesis is the source of all life energy. Photosynthesis is
like breathing. We inhale the oxygen from plants. Then plants
absorb the carbon dioxide produced when we exhale.
Learn how energy gets into our food by watching this short
presentation:
Ecological Niche
Ecological niche describes how an organism or population
responds to the distribution of resources and competitors in an
environment. An ecological niche includes all the resources
available to a species along with the living and nonliving
conditions that may have a favorable or unfavorable impact. Put
another way, an ecological niche refers to all the possible
interactions of a species with other species in a community.
Interactions include the following:
· Competition: This occurs when two or more species compete
for the same resources.
· Predation: Predators are at the top of the food chain in an
ecosystem. Their survival depends on the availability of prey
populations. Big fish eat smaller fish, and so on. Trophic

interaction is a term used to describe feeding behaviors in an
ecosystem.
· Parasitism: Parasites are organisms that live on other
organisms. Many species are subject to parasites. For example,
the Anopheles mosquito feeds on the blood of both animals and
humans. These mosquitos can spread disease-bearing pathogens
like those that cause malaria.
· Mutualism: This describes a mutually beneficial relationship
between unrelated species. Pollination of flowering plants
(angiosperms) offers a prime example. Bees collect pollen as a
source of nutrients. As they move from flower to flower, they
spread pollen to other angiosperms. This enables the
reproduction (pollination) of flowering plants. Thus, bees and
angiosperms have a mutual relationship.
All of the above are important, along with abiotic factors such
as climate and soil type. Informally, a niche is thought of as the
“role” played by a species within a community or habitat.
Biomes
A biome is different from an ecosystem. An ecosystem
describes the interaction of living and nonliving things in an
environment. A biome, on the other hand, is a specific
geographic area that can be identified by the species living
there. A biome is made up of many ecosystems. For example,
the aquatic biome includes a number of ecosystems. These
include ecosystems associated with phytoplankton, coral reefs,
kelp forests, fish, and so on.
The five major biomes of planet Earth include desert, tundra,
aquatic, forest, and grassland biomes.
· Desert BiomesDesert biomes cover about one-fifth of Earth’s
land surface. Deserts form due to the low level of rainfall in an
area. A primary characteristic of all deserts is low species
diversity, including reptiles and small mammals like field mice
and gophers.
Four major types of deserts exist in this biome: hot and dry,
semiarid, coastal, and cold. Hot and dry deserts include the

Sahara, the Arabian Peninsula, central Australia, and the
Mojave Desert in the American Southwest. Semiarid deserts can
be found in areas of Utah, Montana, and the Great
Basin. Coastal deserts include the far northwestern Sahara
where it borders the Atlantic Ocean, and the Atacama Desert of
Chile, which borders the Pacific Ocean. Cold deserts are found
in places like Antarctica and Greenland.
We’ll return to this topic later, as we consider the nature and
extent of desertification in general as well as within our current
era of climate change and global warming.
· Tundra BiomesTundra biomes are the coldest of all the
biomes. The word “tundra” comes from the Finnish
word tunturia, which means “treeless plain.” Frosty landscapes,
extremely low temperatures, and little precipitation characterize
tundra. Tundra biomes are poor in nutrients and follow short
growing seasons. There are two types of tundra: arctic tundra
and alpine tundra.
Arctic tundra refers to the Arctic region in the northern
hemisphere, around the North Pole. Alpine tundra refers to
mountain regions at high altitudes. In these areas, trees can’t
grow and nighttime temperatures are below freezing.
· Aquatic BiomesAquatic biomes fall into two groups:
freshwater and oceanic (marine). Freshwater biomes include
lakes, ponds, streams, rivers, and marshes or wetlands. Oceanic
biomes cover about 75 percent of Earth’s surface, making them
the largest biomes on the planet. The five main ocean biomes
include the Pacific, Atlantic, Indian, Southern, and Arctic
Oceans. Together, they link a huge number of ecosystems.
Lesser oceanic sub-biomes include bays, gulfs, and estuaries.
Life on Earth began in the oceans. For about a billion years,
Earth’s surface was sterile. Surface life only began as plants
spread inland and pumped oxygen into the atmosphere.
Eventually, the ratio of oxygen to nitrogen in the atmosphere

reached 21 percent. This ratio allowed amphibians to come
ashore and air-breathing creatures to evolve. (Did you know
that the ion balance in human blood serum is roughly identical
to the ion balance of ancient oceans? That’s why it’s
recommended that people switch from iodized salt to sea salt.)
Earth’s oceans are critical to survival of all life on the planet.
They regulate global climate patterns. They’re also the source
of the water cycle, which is initiated as the surface evaporates.
Of course, oceans are also home to millions of fish species,
aquatic mammals (dolphins, whales), plankton, phytoplankton,
mollusks, jellyfish, and so on. Phytoplankton provides most of
the oxygen in the air through photosynthesis. Indeed, these tiny
organisms are the basic foundation of the oceanic food chain—
not to mention the foundation for all life on Earth.
· Forest BiomesForest biomes include three main types—
tropical rainforests, temperate forests, and boreal forests (also
called taiga). These three kinds of forests once occupied about
70 percent of the planet’s surface. Today, due largely to
deforestation, pollution, and industrial and agricultural
activities, forests occupy only about one-third (30 percent) of
Earth’s land area.
Tropical forests are confined to regions near the equator. These
forests harbor the largest array of species of all kinds. They’re
also a significant source of atmospheric oxygen. The largest of
the tropical forests on Earth is the Amazon basin. This area is
sometimes called our planet’s “lungs” because of the volume of
atmospheric oxygen it supplies. Other major tropical forest
areas include the Guyana Shield of northern South America
(from Guyana to Venezuela to Colombia and Ecuador), as well
as regions of Indonesia, Malaysia, Vietnam, Cambodia,
Thailand, and southernmost India. They also include Africa’s
Congo Basin (“the Congo”) in Central Africa. This region
includes the Democratic Republic of the Congo and extends into
highland regions of Uganda, Rwanda, and Burundi, where we

find the threatened domain of the mountain gorilla.
The deforestation of tropical rainforests in Brazil and Southeast
Asia is a problem. Deforestation deprives the planet of precious
resources found only in rainforests. This includes amazing
species diversity, an unknown number of medicinal herbs (many
pharmaceutical drugs originated from tropical medicinal herbs),
and, of course, the oxygen pumped into the atmosphere.
Subtropical forests constitute a subdomain of tropical forests.
They represent a transition zone from tropical forests to higher-
latitude temperate forests. In the United States, Florida and the
Gulf Coast states are thought of as subtropical climate regions.
However, in most of this region, subtropical forests are mainly
noticeable by their absence. In much of this region, forests and
wetlands have been destroyed for urban residential development
as well as agricultural and industrial development. Of course,
the same may be said of temperate forests worldwide.
Temperate forests, as suggested by their name, occupy Earth’s
temperate latitudes. These are the regions from 40 to 60 degrees
latitude in the northern and southern hemispheres. In Europe,
temperate forests can be found from northwestern Europe to the
Arctic Circle in Scandinavia. North American temperate forests
include the temperate rainforests of the U.S. Pacific Northwest
and Canada’s British Columbia. Otherwise, temperate forests
remain in the eastern United States and portions of southeastern
Canada. In Asia, temperate forests exist in western Russia,
northeast China, and Japan. In the southern hemisphere,
temperate forests cover much less territory. They can be found
in southern Chile, Tasmania in Australia, and South Island in
New Zealand. In general, temperate forests include
both coniferous and deciduous species. (Coniferous trees
produce cones and evergreen needles. Deciduous trees produce
leaves that fall off seasonally.) Temperate rainforests are home
mainly to coniferous (evergreen) species.

In general, deciduous trees are those that produce leaves that
change colors in the fall, drop to the ground, and sprout new
leaves in the spring. Coniferous trees bear needles and cones
and stay green all year round. However, not all trees or shrubs
fall neatly into these categories. Some trees that grow needles
and cones are actually deciduous trees. Some broadleaf trees
and shrubs are neither coniferous nor deciduous. Examples
include rhododendron and mountain laurel. Both are broadleaf
evergreens that stay green all year long. They reproduce in the
same manner as other angiosperms (flowering plants).
Taiga is the Russian name for forest, although in southerly
regions they are called boreal forests. The taiga represents the
world’s largest connecting terrestrial biome, making up about
30 percent of all of Earth’s forests. In Asia, the taiga covers
much of northern Russia and Siberia. Taiga forests are also
found in northern Mongolia and Kazakhstan as well as on the
Japanese island of Hokkaido. In Europe, taiga forests cover an
area that includes northern Norway, Sweden, and Finland. In
North America, boreal forests occupy most of the land area of
the Canadian interior as well as a portion of Alaska.
Spring and fall are barely noticeable in the taiga. Instead,
there’s a short summer season that’s warm and humid. This is
followed by a much longer season during which the closely
packed coniferous trees are covered in frost and snow. If this
season had a message on a sign, it might read, “Hostile to life.
Enter at your own risk.” On the other hand, during the brief
summer, the taiga is a haven for insects, which attract many
species of birds. The birds build nests as they feast on the
insects. A number of animal species are also adapted to life
there. The snowshoe rabbit, for example, changes color from
beige to white. Other year-round animals find ways to adapt to
arctic temperatures. These include moles that tunnel under the
snow, as well as bears, mice, badgers, wolverines, squirrels, and

reindeer (in Eurasia).
· Grassland Biomes
Two main types of grassland biomes exist: savannas and
temperate grasslands. Species diversity, rainfall patterns,
climate zones, and soil types distinguish these biomes from
each other.
Savannahs feature scattered individual trees separated by
grasses. Africa is one example. The savanna covers nearly half
the surface of central Africa, south of the Sahara. A key feature
of the savanna is the alteration of dry and rainy seasons. During
the rainy season, vegetation flourishes. Food can be gathered
and stored. This is followed by a dry season, during which the
land once again becomes parched and dry. Natural or human-set
fires reduce the desiccated vegetation to ash. The ash revitalizes
the soil with nutrients, and vegetation returns. Cattle and native
species can graze the lush landscape. Other species can gather
food. In any case, savannas like this are called climatic
savannahs, as they depend on alternating seasons of wet and
dry.
Another kind of savanna is the derived savannah. This occurs
when land is cleared to make room for farming or cattle
ranching. Downed trees and shrubs are burned to produce ash.
This ash creates viable soil—at least for a few seasons—after
which new land must be cleared for the process to continue.
Derived savannahs have overall negative environmental impact.
For example, this is true of the Sahel that crosses Africa just
south of the Sahara.
Temperate grasslands include a rich mixture of perennial
grasses (grasses that live more than two years) and flowering
plants. These plants are called forbs. Temperate grasslands
presently occupy about 25 percent of Earth’s land surfaces. The
mixture of grasses and forbs produces some of the most fertile

soils on the planet. As a result, most grassland has been
converted for agricultural purposes (farming).
The semi-arid climate of the temperate grasslands varies by
region. That’s because grasslands extend over a wide range of
latitudes. Imagine the distance from Kansas to northern regions
of Alberta, Manitoba, and Saskatchewan in Canada. Over that
range of area, summers may be warm or hot, depending on
latitude. However, in much of this range, winter precipitation
arrives as snow. So, on the plus side, the spring melt provides a
steady source of moisture for the growing season. On the
downside, rapid melting may result in serious flooding.
In North America, grasslands include the high plains of the
prairie states into Canada. In the United States, grasslands can
be found in eastern Washington, parts of California, and in
semi-arid regions of the Southwest. Globally, temperate
grasslands can be found in Argentina, Uruguay, and the Veld
region of South Africa. In Eurasia, the steppes are a type of
grassland. The steppes can be found from the Ukraine west
across central Russian to parts of Mongolia. The steppes played
a major role in advancing humanity, as people there were the
first to domesticate horses. The domestication of horses
changed transportation and the conduct of wars forever.
Typically, grassland fauna are low in diversity, especially as
compared to tropical forests and savannas. In North America,
native species included bison, pronghorn antelopes, and rodent
herbivores such as pocket gophers, ground squirrels, and prairie
dogs. Badgers and coyotes are still around as predators and
scavengers.
To learn more about Earth’s major biomes, check out this video:
Ecological Challenges
Earth from Space
Let’s look at some of the ecological challenges facing the

world. These issues are all related to climate change and global
warming in various ways. As you learn about them, consider
their origin and impact. Think about how they contribute to
climate change and global warming.
Pollution
Pollution is the process of making land, water, or air unsafe for
life. Pollution of the air, water, and soil is a problem for
everyone. For example, in 2014 toxic chemicals were
unintentionally spilled into the water supplies of nine counties
and the city of Charleston in West Virginia. The culprit was a
toxic chemical called 4-methylcyclohexane. The spill may have
been an accident but it was still a catastrophe. The government
issued a ban on the use of tap water for nine days, which barely
made an impact on the ongoing problem. Several hundred
people had to be treated in hospitals for chemical exposure over
the following weeks. Tap water continued to have a peculiar,
lingering licorice odor for some time afterward.
Pollution comes from many sources. For example, water
pollution can come from oils spills, acid rain, and industrial and
farm runoff. These issues also cause problems with soils. Farms
that rely on petroleum-based fertilizers, pesticides, and
herbicides, for instance, have destroyed organism-rich topsoil.
Meanwhile, air pollution comes from emissions from internal
combustion engines. Think about the brown clouds that are
often seen over urban centers. (California has been a recent
exception; in that state, regulatory action has made urban air
more breathable.)
Waste Disposal
Across the globe, the overconsumption of resources has created
a crisis associated with waste—garbage—disposal. Developed
countries in particular produce an enormous amount of garbage.
This garbage is dumped into the oceans or buried in landfills.
The disposal of nuclear waste poses a tremendous health hazard.
The radiation from nuclear waste dumps can remain toxic and
lethal for centuries.
Waste disposal is one of our most serious environmental

problems.
Here are examples of a few waste disposal dangers:
· Chemical spills pose danger to water supplies.
· Landfills and incinerators dump carcinogens and pollutants
into the air. This increases the risks for cancer, asthma, and
respiratory disorders.
· Landfills attract rats, flies, and other carriers of a variety of
communicable diseases.
· Burning waste contributes to the number of greenhouse gases
in the atmosphere. These gases promote global warming and
climate change.
Let’s focus on that last item for a moment. According to one
source, “Asia, Latin America, and Africa alone are to blame for
about 40 percent of methane emissions every year. That 40
percent is equal to about 37 million metric tons of carbon
dioxide.” Further, experts believe that industrialized nations
produce considerably more waste than this. Specifically, “In the
United States, each American produces an average of .75 tons of
trash every year.” That’s the most waste per person per capita in
the world. Europeans are estimated to dispose of about half a
ton of trash annually. In Asia, an average person produces .2
tons of trash each year.
Pollution affects everyone, everywhere. Environmental
problems in Asia can and do affect North America, Europe, and
Africa. For this reason, cooperation among nations is needed to
deal with the waste problem.
Consider, for example, Europe leads in the development of
environmental technologies. In fact, about 60 percent of
environmental discoveries and technologies originate in Europe.
Thus, Europeans can play a major role in raising awareness and
helping other nations to apply workable solutions. China and
India are both high on the list of Asian countries with major
pollution problems, including water and air pollution,
deforestation, and the loss of biodiversity. Other countries can
work with their governments to find workable solutions.
Urban Sprawl

Urban sprawl refers to the uncontrolled expansion of urban
living areas. Urban sprawl means one thing in developed
countries and quite another in developing or underdeveloped
countries. In this lesson, we’ll focus on urban sprawl issues as
they apply in the United States. The complex issues related to
urbanization in the developing world will be considered in
future lessons.
In developed countries, urban sprawl occurs when populations
move from high-density cities into lower-density surrounding
areas. The era of urban sprawl in the United States began during
the period of economic prosperity following World War II. It
was made possible in large part by the progressive reforms
initiated under President Franklin Roosevelt’s “New Deal.”
Labor unions were strong, and corporations embraced fair labor
practices. There were plenty of good jobs with benefits. The
G.I. Bill allowed a whole generation of young men to obtain a
college education, and the future looked bright. Consumer
demand soared. The philosophy of consumerism soared. The
“American Dream” was linked to owning a home, sophisticated
appliances, and the latest model of automobile. The rush to the
suburbs became a stampede, which came at a serious cost. Let’s
look more closely.
Increased Air Pollution
According to the Sierra Club, the typical annual commute from
the suburbs to the workplace involves about eight workweeks of
55 hours each. That’s 440 unpaid hours sitting behind the wheel
of an automobile. More driving leads to an increase in air
pollution, in addition to health risks due to inhaling exhaust
fumes and smog.
Overconsumption of Water
Urban sprawl means a larger ecological footprint for people. As
people spread out and population density increases, water
distribution problems arise. One of these problems is the result
of a demand for water to landscaping. According to the EPA,
about 30 percent of daily water in the United States is used
outdoors. People water their lawns and golf courses, grow

flowers and plants, and fill their outdoor pools. Review this site
for more details: Understanding Your Own Water Use
Increased Risk of Obesity
According to the Ontario College of Family Physicians and the
American Planning Association, life in the suburbs is associated
with higher rates of obesity. This can partially be blamed on the
consumption of processed foods and fast-food restaurants.
However, experts also agree that obesity has risen due to
overuse of automobiles for traveling even short distances.
In many places, people in the suburbs must drive to go
anywhere. They spend too much time sitting in the car instead
of walking where they need to go. In short, too little exercise
can lead to an excess of weight on the body.
For more information on the relationship between urban sprawl
and obesity, visit these sites:
· Effects of Urban Sprawl on Obesity
· Relationship Between Urban Sprawl and Physical Activity,
Obesity, and Morbidity
Obesity is very problematic for people. It increases the risk of
high blood pressure, cardiovascular disease, and diabetes,
among other health concerns.
Loss of Wildlife Habitat
Wherever there’s urban sprawl, native wildlife suffers. Today,
some 60 percent of native wildlife lives within metropolitan and
suburban regions. Some of these species, such as black bears,
whitetail deer, skunks, redtail hawks, starlings, and opossums,
have adapted to populated environments. Even though these
animals lived in suburban areas first, residents often view these
species as annoyances. They look for ways to eliminate or
minimize them.
For more detail on species endangered by urban sprawl, visit
this site: Endangered by Sprawl
The list of threatened and endangered species is quite long. In
Virginia alone, the U.S. Fish and Wildlife Service reports these
numbers on their list of threatened or endangered species:
· Amphibians and reptiles: 7 (Most of them are species of sea

turtles.)
· Birds: 4 (Example: The red-cockaded woodpecker is
endangered because 97 percent of its habitat range has been
destroyed.)
· Fishes: 8 (Example: The Atlantic sturgeon is now listed as
engendered throughout the Chesapeake Bay due to overfishing
and habitat destruction.)
· Mammals: 5 (Three of these species are bats coping with
habitat destruction.)
· Mussels and other invertebrates: 31 (Again, in most cases the
culprit is habitat destruction.)
· Plants: 17 (Another result of habitat destruction, especially in
the Appalachian highlands.)
Total: 72. And that’s for just one state. Urban sprawl is
endangering wildlife all across America.
Artists Speak: Characterizing Urban Sprawl
Sometimes we can better understand the dry statistics of topics
like urban sprawl by listening to the voices of the arts, in this
case, protest ballads. Recall that advances in technology may be
at odds with cultural ideals. Below we’ll get a perspective on
the suburbs from an article written by Angie Schmitt:
“The protest movements that have changed the world—for
peace, civil rights or labor justice—have always had rallying
songs that inspired devotees and informed the masses. The
smart growth movement is no exception: sprawl and the general
shortcomings of the American suburb have been a favorite
theme among musicians ever since the invention of the cul-de-
sac.
Rock music … literally teems with songs about loneliness,
alienation, disaffection, conformity, overbearing authority, and
general malaise as they relate to the modern suburban
landscape. And as time has gone on, the cries have only gotten
louder.
The first musical rattling of protest began nearly as soon as
sprawl itself in the early 1960s. One of the first hits of this
genre is Malvina Reynolds’s ‘Little Boxes,’ written in 1962 and

made famous by Pete Seeger the following year. More recently,
it was picked up by Showtime as the theme song for the
suburban melodrama Weeds. Like many of its type, the song
dwells on themes of conformity, material excess and spiritual
poverty.
Little boxes on the hillside / Little boxes made of ticky
tacky,Little boxes on the hillside / Little boxes all the
same.There’s a green one and a pink one / And a blue one and a
yellow one,And they’re all made out of ticky tacky / And they
all look just the same.
Another classic is Joni Mitchell’s ‘Big Yellow Taxi,’ recorded
in 1970. The song was inspired by a trip to Hawaii. When
Mitchell looked out her hotel window, she saw a beautiful vista,
marred by a large parking lot. The trip also . . . included a trip
to the Honolulu Botanical Garden, which contained many rare
and endangered tropical plants.
They took all the trees / Put ’em in a tree museumAnd they
charged the people / A dollar and a half just to see ’emDon’t it
always seem to go / That you don’t know what you’ve got till
it’s goneThey paved paradise / And put up a parking lot”
Depletion of the Ozone Layer
The ozone layer is found in Earth’s stratosphere. It provides a
natural shield against harmful ultraviolet radiation (UV) from
the sun. The ozone layer is composed of ozone gas. In fact,
about 90 percent of all ozone in Earth’s atmosphere is found in
this layer. (Most of the remaining 10 percent hovers near
Earth’s surface as an atmospheric pollutant.) Ozone is important
because it provides protection for the planet and allows
species—including humans—to thrive. However, it’s also
considered a toxic pollutant when it’s close to Earth. Ozone gas
is one of the main components of urban smog.
To learn more about ozone, visit this site: Science: Ozone
Basics
The stratosphere has that name because it’s stratified, or formed
in layers. There are higher and lower layers. As one moves
upward through the layers of the stratosphere, the atmosphere

gets warmer. That’s because heat (energy) gets released as
ozone interacts with ultraviolet (UV) radiation from the sun.
These interactions essentially “devour” UV radiation.
Starting in the 1970s, scientists noticed the thinning of the
ozone layer. This was especially noticeable over Antarctica,
where an “ozone hole” was appearing. Note this isn’t an actual
hole; rather the ozone at that location is vanishingly thin. In any
case, as the ozone situation became known, scientists began to
realize that human activity was the root of the problem. Experts
identified the main eater of the ozone
as chlorofluorocarbons (CFCs). CFCs are chemicals that
combine molecules of carbon, chlorine, and fluorine. They’re
used for many industrial purposes. However, they’re especially
used for refrigerants, plastics production, and as propellants in
aerosol cans. As these gases move upward in the stratosphere,
they eat away at ozone in the stratosphere.
It’s clear that CFCs are potent greenhouse gases. International
agreements such as the Kyoto Protocol seek to replace the use
of CFCs with other substances, such
as hydrofluorocarbons (HFCs). That has helped. The ozone
layer is being gradually restored, and one kind of greenhouse
gas has been sidelined. On the other hand, HFCs have also been
identified as potent greenhouse gases. This raises the question:
should plastics be abandoned worldwide? (This makes sense for
many reasons, including waste management. Consider that the
three “dead zones” in the Pacific Ocean are essentially
enormous floating landfills, full of decayed plastics.)
By the way, before you spend time in a tanning bed, think
twice. There are two kinds of ultraviolet light, UVB and UVA.
UVB causes sunburn and can cause cancers such as basal cell
and squamous cell carcinomas. Worse yet, UVB can penetrate
the skin of organisms—both plants and animals—and cause
permanent DNA damage. However, UVA, which is used in
tanning beds, is far from risk-free. It’s now known that UVA
can cause melanoma, a deadly skin cancer. UVA also leads to
premature aging of the skin.

The ozone layer is linked to another ecological
challenge, deforestation, which we’ll cover a little later. In
simple terms, trees offset the effects of greenhouse gas
emissions by serving as carbon sinks. That is, trees and plants
are able to soak up carbon dioxide in the atmosphere while also
replenishing oxygen. However, deforestation—the removal of
trees—upsets this process. One way to fix the ozone problem is
to plant more trees: as many as possible, in as many places as
possible. This helps to check global greenhouse
emissions and repair the ozone layer.
Acid Rain
Acid rain is produced by burning fuel that includes sulfur
dioxide (SO2) and nitrogen oxides (NO, NO2). Acid rain may
arrive as rain. However, it may also arrive in the form of snow,
dew, hail, or fog. Acid rain (sometimes called acid
precipitation) in any form is damaging to plants, animals, and
humans.
How does acid rain form? Gases from burning fuel rise to the
high atmosphere. There, they undergo chemical reactions with
oxygen, carbon dioxide, water, and sunlight. Through this
process, the gases are converted to sulfuric and nitric acids.
Eventually, these acids make their way back to the planet in the
form of acid rain (or other precipitation). Acid rainfall alters
environments in ways that are unfriendly to humans and other
living things.
Some acid rain occurs naturally through processes like the
rotting of some types of vegetation and volcanic eruptions.
However, most acid rain is a result of human activities. Burning
coal in electric power plants is a major source of acid rain.
According to the EPA, about two-thirds of sulfur dioxide and
nitrogen oxide emissions in the United States come from
electric power generators. Other culprits include motor vehicles
and heavy equipment, as well as manufacturing and oil
refineries.
In developed countries, high levels of nitrogen oxide emissions
are associated with large urban centers. That’s because

populations in those areas are dense and auto traffic is heavy.
However, where the wind blows, nitrogen oxide follows. For
example, heavily polluted air over industrial China can impact
the American Midwest. Similar, nitrogen-oxide laden air from
American industrial regions can damage the evergreen forests of
Europe. Acid rain pollution is a global problem that can be
addressed only through global cooperation.
Review the graphic below. It shows how the sources of primary
pollutants produce secondary pollutants, which return to the
planet’s surface as acid rain.
Primary and Secondary Pollutants
(Public domain image)
https://www.environment.gov.scot/educational-resources/get-
learning/air/
Acid rain has many negative effects, including the following:
· Acid rain can cause extensive damage to trees. Damage to
leaves can deprive forest soils of nutrients they need. This
makes them more vulnerable to environmental stress and
disease.
· Fish and wildlife populations decline in areas impacted by
acid rain.
· Acid rain can alter the chemical properties of soil, impacting
agricultural production. Microbiological processes in the soil
become less efficient. This reduces the availability of vital
nutrients and stunts root system growth.
· Acidic water passing though water pipes can leach copper and
lead into the water supply that people drink. Although this can
be somewhat addressed through modern water purification
techniques, not everyone has access to water that’s been
properly treated. People who depend on well water, for
example, may be at risk for toxic effects of the leached metals.
· Acidic fog can lead to respiratory disorders like asthma. It can
also cause eye, ear, and throat irritations. The risks are greatest
among the elderly and those with chronic respiratory problems
such as emphysema and COPD.
· All human-made structures tend to deteriorate over time.

However, buildings, statues, tombstones, and monuments
(especially when crafted from limestone) exposed to acid rain
tend to deteriorate at a faster rate. Acid rain also speeds up the
process by which metal corrodes, affecting motor vehicles and
exposed steel structures.
Deforestation
Humans have been engaging in deforestation practices for a
long time in history. Industrialization has marched hand in hand
with the clearing of forests. In fact, in the continental United
States, about 90 percent of indigenous forests have been
destroyed since 1600.
As already noted, most remaining indigenous boreal forests are
located in central Canada, Alaska, northern Russia, northern
Japan, and northern Mongolia. The largest remaining indigenous
tropical forests are found in the northwestern Amazon Basin and
in the Guyana Shield of South America. This region includes
Guyana, Surinam, Venezuela, Colombia, and Ecuador. Other
regions with extensive tropical forests include Indonesia,
Cambodia, Vietnam, Thailand, southern India, and the Congo
Basin in the Democratic Republic of the Congo.
Global forests act as carbon sinks by absorbing carbon dioxide
while also uploading oxygen into the atmosphere. Carbon sink
capacity is vital—and obviously reduced as forests are cleared.
This adds heavily to global greenhouse gas production and
contributes to global warming. Additionally, trees and other
kinds of vegetation emit carbon dioxide when they die.
To learn more about how carbon sinks work, watch this video:
According to the EPA, the most
significant anthropogenic (human-caused) source of global
warming is the burning of fossil fuels. The second major cause
is deforestation, particularly the destruction of tropical forests.
According to NASA, if the current rate of deforestation isn’t
curbed radically, the world’s rainforests may be completely
destroyed in as few as 100 years.
Deforestation clearly affects the carbon cycle. However, it also
disrupts the hydrologic (water) cycle. Trees, especially those in

tropical forests, emit water vapor. Global climate is regulated
by water vapor in the atmosphere. This vapor is also considered
the world’s chief greenhouse gas. Thus, changes to the water
cycle inevitably lead to changes in global climate patterns.
Deforestation is also a major factor in the global decline of
species diversity. According to the National Geographic
Society, some 70 percent of Earth’s plants and animals are
impacted by the destruction of native habitats. Some species can
adapt to changes in their native habitats. Some may be able to
migrate to other locations. But others can’t adapt and become
extinct.
Finally, deforestation leads to soil erosion. Tree roots serve as
anchors. When these roots are destroyed, soil may be washed or
blown away. According to the World Wildlife Fund (WWF),
upward of one-third of the planet’s arable land has been lost to
deforestation just since 1960. Part of the problem is clear-
cutting forests to grow cash crops like coffee, palm oil, and soy.
These crops don’t have root systems capable of anchoring the
soil. That makes erosion more likely.
Desertification
From an ecological perspective, all of Earth’s biomes are
headed in the wrong direction. That’s clearly evident when it
comes to the process called desertification. This is the process
by which fertile land becomes desert. According to UNESCO,
globally, “Twenty-four billion tons of fertile soil disappears
annually. Over the past 20 years, the surface area lost is equal
to all of the farmland of the United States.” This means roughly
one-third of the world’s land surface is threatened by
desertification. This threatens food production, which is
particularly problematic for soaring populations, especially in
less developed nations.
Desertification is caused by the destruction or removal of
“green” coverage. Although there are many reasons for this, the
two primary causes are human activity and climate change.
Globally, desertification results from human overexploitation of
natural resources. For example, in regions like Africa and the

Middle East, the burning of firewood for energy is a major
problem. In the long term, these drought-plagued regions must
turn to renewable energy sources based on solar, hydrological,
and wind technologies. In the short term, the use of natural gas
and petrol is preferable to stripping the land for firewood.
In semi-arid environments prone to desertification, three human
activities are of major concern.
· Overcultivation exhausts the soil, reducing vital nutrients.
· Overgrazing by poorly managed livestock strips away the
vegetation cover. Overgrazing encourages erosion and
deforestation.
· Improper irrigation leads to an increase in salt levels of
croplands. (This is called salinization.) The salty environment is
hostile to healthy plants.
Desertification is especially problematic in certain parts of the
world. Over many decades, political and economic instability
has wreaked havoc in Western Asia and North Africa. Unfair
trade practices that impact oil-producing nations in Western
Asia have been part of the problem.
Evidence of Global Warming and Climate Change
Are humans facing extinction? This is not a rhetorical question.
Mounting evidence from various scientific sources suggests that
humans are in denial about their peril. Scientific reports are
dire, but experts believe we still have time to address these
issues and reverse the situation.
Experts rely on information provided by observable data.
Studies show that land and ocean surfaces are warming at an
unprecedented rate. We can observe rising sea levels,
accelerating desertification, and a higher frequency of weather
patterns like tornadoes, hurricanes, and tsunamis. We can also
observe unnatural patterns of desertification and precipitation.
This evidence shows that global warming and climate change
are observable.
Greenhouse Effect
Earth’s natural environment is changing due to the greenhouse

effect. To understand the greenhouse effect, study the image
below. On the left you’ll see that the surface of the planet is
warmed even as a surplus of heat is radiated back into space. On
the right you’ll see how greenhouse gas molecules absorb
infrared (heat radiation) and scatter it over the planet.
Greenhouse gases include water vapor, carbon dioxide, and
nitrogen oxides emitted by burning fossil fuels like coal and
petroleum. Methane (CH4) is another greenhouse gas. Methane
is a component of natural gas that is used in a number of
industrial processes. Foremost among these are the gas and
petroleum industries.
Methane also gets into the atmosphere from other sources. For
example, landfills emit methane, as do wetlands and areas of
cattle ranching. Methane stored in long-buried vegetation is
being released into the atmosphere as the arctic permafrost has
melted due to global warming.
We don’t know exactly what this means. However, the ratio of
methane to other greenhouse gases has been increasing at an
alarming rate. This is a serious issue. Although methane doesn’t
linger for a long time in the atmosphere, it’s eight times more
potent than carbon dioxide over the short term.
The Mechanics of Global Warming
How does global warming work? Water vapor is our planet’s
“thermostat.” It’s also our chief greenhouse gas and the key to
regulating Earth’s temperature. However, as NASA researchers
have established, an increase in carbon dioxide and other
greenhouse gases amplify the “thermostat” setting. At its
current rate of emissions, carbon dioxide alone can double the
heat retention of water vapor in the atmosphere. As global
warming increases the amount of water vapor in the atmosphere,
we observe a positive feedback loop. (This means the rise in
temperature is accelerated.) As a result, we end up with a “new
normal,” like daily temperatures exceeding 120 degrees
Fahrenheit in parts of Pakistan.
Let’s look at the Keeling curve.
The Keeling Curve

(NOAA public domain image)
The Keeling curve is a graph used to plot the ongoing change in
carbon dioxide in Earth’s atmosphere. It is one of the best-
known, ongoing studies of the relationship between carbon
dioxide and global warming. The Keeling curve is named for
Charles David Keeling. He was a scientist who began tracking
carbon dioxide levels at Mauna Loa, Hawaii, in 1958. He
continued to direct the study until his death in 2005.
Notice on the graph that the the carbon dioxide level in Earth’s
atmosphere exceeded 400.00 parts per million (ppm) in 2013.
The last time carbon dioxide exceeded this rate was millions of
years ago—long before the emergence of the human species.
Another important indicator of global warming is the rate of
arctic ice melt. That rate is known to correlate to rising levels
of carbon dioxide in the atmosphere. Study the image provided
by the National Oceanic and Atmospheric Administration
(NOAA).
Average Sea Ice Concentration on Earth
NOAA public domain image
The image shows that the rate of polar cap melt is
another positive feedback loop. That is, as the Arctic polar ice
melts due to global warming, dark ocean surface areas expand.
This causes more heat to be stored in the polar environment,
leading to more ice melt, and so on. The feedback loop is called
“positive” because it amplifies changes in a system.
Species Extinction
You had a brief preview on species extinction during the
discussion of urban sprawl. There you learned that human
destruction of natural habitats is the main cause of species loss
in the United States. This observation can also be applied
worldwide.
A number of recent studies make it clear that humans are
responsible for the extinction of many species. However, the
topic is extremely complex. It’s difficult to establish current
species extinction rates for a number of reasons. For one,
experts cannot accurately determine the actual number of

species on the planet. Consider this quote from the World
Resources Institute as reported by the World Wildlife Fund:
“Scientists were startled in 1980 by the discovery of a
tremendous diversity of insects in tropical forests. In one study
of just 19 trees in Panama, 80 percent of the 1,200 beetle
species discovered were previously unknown to science . . .
Surprisingly, scientists have a better understanding of how
many stars there are in the galaxy than how many species there
are on Earth.”
Extinction is a natural phenomenon. In fact, it’s been estimated
that 99 percent of all species that have lived on Earth are now
extinct. However, this extinction occurred at a
natural background rate of about one to five species per year.
Scientists now conservatively estimate that the planet is losing
species at 100 to 1,000 times this rate. That means dozens of
species are going extinct every day.
Scientists generally agree that extinction rates have reached
levels not seen since the dinosaurs died out 66 million years
ago. Some theories claim that dinosaurs died out after a huge
asteroid hit the planet near the Yucatan Peninsula. Humans are
the current “asteroid.” The rate of species extinction in the
human (anthropogenic) era is much faster than in the era of the
dinosaurs.
According to your required reading (in Science Advances),
species are dying off due to
· Clearing of land for farming, logging, and settlement
· Introduction of invasive species to native habitats
· Release of carbon emissions that drive climate change and
ocean acidification
· Introduction of toxins that alter and poison ecosystems
Paul Ehrlich, author of The Population Bomb, was one of the
scientists who wrote the article in Science Advances. According
to the authors, there’s still hope for the future. “Avoiding a true
sixth mass extinction will require rapid, greatly intensified
efforts to conserve already threatened species, and to alleviate
pressures on their populations—notable habitat loss,

overexploitation for economic gain and climate change.”
Ocean Acidification
Although the burning of fossil fuels has increased carbon
dioxide levels in the atmosphere, the oceans have helped slow
down the inevitable impacts of the greenhouse effect. In effect,
the oceans act as huge carbon sinks. About 50 percent of
human-generated carbon dioxide is being stored in the world’s
oceans. Recent studies have shown that, as a result, the oceans
are becoming more acidic. When carbon dioxide dissolves in
water, it produces carbonic acid. The increase of carbonic acid
in ocean waters has caused oceanic pH to drop.
pH is a measure of acidity and alkalinity of a substance. The pH
scale ranges from 0 to 14, with 7 being considered neutral. A
pH reading below 7 is considered acidic. A pH reading above 7
is considered alkaline (base).
The average ocean pH has dropped from 8.2 to 8.1. That doesn’t
sound like much, but even small changes impact marine life. For
example, some types of marine life depend on calcification.
This is the process by which organisms form shells. Oysters,
shrimp, clams, mussels, lobsters, and some species of fish
corals all engage in calcification. Coral reefs depend upon
calcification to grow. High acidity of ocean water makes it more
difficult for these species to produce their shells.
Additionally, acidic water can have a dramatic impact on
plankton and phytoplankton, which are the base of the oceanic
food chain. These microscopic organisms drift or float and are
eaten by many larger organisms. For example, whales thrive on
plankton, as do many other oceanic species. An increase in
acidity is expected to spur a range of responses in plankton and
phytoplankton. Some species will die out, while others will
begin to flourish. This dynamic can seriously change the marine
ecosystem that produces 50 percent of our oxygen on the planet.
References
“Acid Rain.” National Atmospheric Deposition Program, 2014.
Retrieved May 22, 2018, from
http://nadp.sws.uiuc.edu/educ/acidrain.aspx

Biello, David. “Risks of Global Warming Rising: Is It Too Late
to Reverse Course?” Scientific American, February 27, 2009.
http://www.scientificamerican.com/article/risks-of-global-
warming-rising/
Bradford, Alina. “Deforestation: Facts, Causes & Effects.”
LiveScience, last updated April 3, 2018. Retrieved May 22,
2018, from http://www.livescience.com/27692-
deforestation.html
Chu, Jennifer. “Ocean Acidification May Cause Dramatic
Changes to Phytoplankton.” MIT News, July 20, 2015.
Retrieved May 22, 2018, from http://news.mit.edu/2015/ocean-
acidification-phytoplankton-0720
“Deforestation.” National Geographic. Retrieved May 22, 2018,
from
http://environment.nationalgeographic.com/environment/global-
warming/deforestation-overview/
DeVos, J.M., et al. “Estimating the Normal Background Rate of
Species Extinction.” Conservation Biologyvol. 29, no. 2 (April
2015). Retrieved May 22, 2018, from
https://www.ncbi.nlm.nih.gov/pubmed/25159086
“Earth’s Atmospheric Layers.” NASA, January 22, 2013.
https://www.nasa.gov/mission_pages/sunearth/science/atmosphe
re-layers2.html
“Endangered and Threatened Species in Virginia.” US Wildlife
Service, February 4, 2014. Retrieved May 22, 2018, from
http://www.fws.gov/endangered/map/va-info.html
Ewing, Reid and Kostyack, John. “Endangered by Sprawl.”
National Wildlife Federation, 2005. Retrieved May 22, 2018,
from
http://www.nwf.org/~/media/PDFs/Wildlife/EndangeredBySpra
wl.ashx
Gleason, Karin. “Science: Ozone Basics.” NOAA, March 20,
2008. Retrieved May 22, 2018, from
http://www.ozonelayer.noaa.gov/science/basics.htm

“How Many Species Are We Losing?” World Wildlife
Foundation. Retrieved May 22, 2018, from
http://wwf.panda.org/about_our_earth/biodiversity/biodiversity/
“How We Use Water.” USEPA. Last updated February 5, 2018.
https://www3.epa.gov/watersense/our_water/water_use_today.ht
ml
Leonardo, R. “Negative Effects of Urban Sprawl.” Home
Guides. Retrieved May 25, 2018, from
http://homeguides.sfgate.com/negative-effects-urban-sprawl-
1716.html
“Man and the Biosphere Programme.” UNESCO, 2017.
http://www.unesco.org/mab/doc/ekocd/chapter1.html
Molar-Candanosa, Roberto. “2015 State of the Climate: Carbon
Dioxide.” NOAA Climate.Gov. August 2, 2016. Retrieved May
22, 2018, from https://www.climate.gov/news-features/featured-
images/2015-state-climate-carbon-dioxide
“Ozone Layer Depletion, Its Causes and Remedies.” QSArticle,
July 29, 2013. Retrieved May 22, 2018, from
http://www.qsarticle.com/ozone-layer-depletion-its-causes-and-
remedies/
“Pollutants and Sources.” USEPA, February 23, 2016. Retrieved
May 22, 2018, from
https://www3.epa.gov/airtoxics/pollsour.html
“Pristine Seas.” National Geographic, updated 2018. Retrieved
May 22, 2018, from
http://ocean.nationalgeographic.com/ocean/explore/pristine-
seas/critical-issues-ocean-acidification/
Rafferty, J. P. “Urban Sprawl.” Encyclopedia Britannica, May
12, 2017. Retrieved May 22, 2018, from
http://www.britannica.com/topic/urban-sprawl
“Resources.” AIRS, Jet Propulsion Laboratory, CA Institute of
Technology. Retrieved May 22, 2018, from
https://airs.jpl.nasa.gov/resources
Schmitt, Angie. “Sprawl’s Greatest Hits: A History of Suburban

Protest Ballads.” StreetsBlog USA, July 29, 2011. Retrieved
May 22, 2018, from
http://usa.streetsblog.org/2011/07/29/sprawls-greatest-hits-a-
history-of-suburban-protest-ballads/
“The Ecosystem and How It Relates to Sustainability.”
Introduction to Global Change, Regents of the University of
Michigan, October 31, 2008. Retrieved May 22, 2018, from
http://www.globalchange.umich.edu/globalchange1/current/lectu
res/kling/ecosystem/ecosystem.html
“Volume 3: Obesity.” The Health Impacts of Urban Sprawl,
Ontario College of Family Physicians. Retrieved May 22, 2018,
from http://ocfp.on.ca/docs/default-source/default-document-
library/urban-sprawl-volume-3-obesity---
2005578c944a146060099dafff0000832dca.pdf?sfvrsn=0
“Water Cycle.” USGS, US Department of the Interior. Last
updated December 2, 2016. Retrieved May 22, 2018, from
https://water.usgs.gov/edu/watercycleprecipitation.html
“World’s Biomes.” UC Berkeley, April 2004. Retrieved May 22,
2018, from
http://www.ucmp.berkeley.edu/glossary/gloss5/biome/
Woodward, Susan. (2012). “Temperate Grasslands.” Department
of Geospatial Science, Radford University. Retrieved May 22,
2018, from
https://php.radford.edu/~swoodwar/biomes/?page_id=173

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