Environmental Science

7. Use your hand lens to inspect the area. Be careful not to dis- ̈ Site Maps Your site map should
turb the soil or the organisms. Then record the types of be as detailed as possible, and it
insects and plants you see. should include a legend.

8. Collect a small sample of soil, and observe it with your hand
lens. Record a description of the soil and the organisms that
live in it.

Analysis

1. Organizing Data Return to the classroom, and display your
site map. Use your site map, your classmates’ site maps, and
your notes to answer the following
questions. Write your answers in
your notebook.

2. Analyzing Data Write one para-
graph that describes the 10 m ҂
10 m site you studied.

3. Analyzing Data Describe the
2 m ҂ 2 m site you studied. Is
this site characteristic of the
larger site?

Conclusions

4. Interpreting Conclusions What
are the differences between the
areas that your classmates stud-
ied? Do different plants and
animals live in different areas?

5. Making Predictions As the
seasons change, the types of
organisms that live in the area
you studied may also change.
Predict how your area might
change in a different season or
if a fire or flood occurred. If possible, return
to the site at different times throughout the year
and record your observations.

Extension

1. Asking Questions Based on what you have learned, think
of a question that explores how the components of the area
you observed interact with each other. For example, you
might want to consider the influence of humans on the site;
study a particular predator/prey relationship; or explore the
effects of physical features, such as water or sunlight, on the
growth or behavior of organisms. Write a description of
how you would investigate this topic. WRITING SKILLS

Chapter 1 Exploration Lab 29

CHICKEN OF THE TREES most often destroy when convert- In the first five years of her
ing forestland to farmland. People project, more than 80,000 iguanas
In the stillness of predawn, the air cut down the forest at its edges— were released into the wild.
warms over the Carara Biological which just happens to be prime Ordinarily, less than 2 percent of
Preserve in Costa Rica. Several habitat for iguanas and other all iguanas survive to adulthood in
thousand eggs in sun-heated incuba- plants and animals. the wild, but Dr. Werner’s iguanas
tors just below the surface of the have a 77 percent survival rate.
Earth stir in response. Within these Back at the Iguana Dr. Werner knows this because
eggs are tiny iguanas—lizards that Ranch after she releases the iguanas into
will eventually emerge, grow to a the rain forest, the lizards are
length of 1.5 m to 2.0 m (5 ft to 6.5 Dr. Werner’s “iguana ranch” tracked and monitored to deter-
ft), and weigh up to 6 kg (13 lb). preserve has artificial nests where mine whether they have success-
females can lay their eggs in a fully adapted to life in the wild.
What’s going on here? Well, predator-free environment. After
these giant lizards are being raised they hatch, the young lizards are Passing It On
so that they can be released into placed in a temperature- and
the rain forest. It’s part of a project humidity-controlled incubator and Since the 1980s, Dr. Werner has
led by German-born scientist Dr. given a special diet. As a result, the improved the iguanas’ chances of
Dagmar Werner. Her goal is to iguanas grow faster and stronger survival by breeding them and
help restore an iguana population and are better protected from releasing thousands of young igua-
that has been severely reduced in predators than their noncaptive nas into the wild. But Dr. Werner
the past several decades. counterparts. soon realized that this effort was
not enough, so she began training
The lizard has suffered from the other people to do the same.
effects of hunting, pollution, and
habitat destruction by people who Because she knew there was no
clear the rain forest for farming. time to lose, Dr. Werner took an
Prime iguana habitat is at the edge immediate and drastic approach to
of the forest—where a combination solving the problem. She combined
of open areas, scrub, and trees her captive-breeding program at
occur. Historically, these areas are the preserve with an education pro-
the type of habitat that humans gram that shows farmers that there
is more than one way to make a
̈ These are iguanas at the Carara profit from the rain forest. Instead
Biological Preserve in Costa Rica.

̈ Dr. Werner and an associate dis-
cuss how the iguana can be farmed.

of raising cattle (and cutting down never thought of wild animals as heighten awareness about the
rain forest to do so), she encour- creatures that must be protected in iguana’s economic importance.
ages local farmers to raise iguanas, order to survive. That’s why so
which can be released into the wild many go extinct.” To get her mes- By demonstrating that the needs
or sold for food. Known as the sage across, Dr. Werner has estab- of all concerned parties can be met
“chicken of the trees,” this lizard lished the Fundación Pro Iguana when attempting to save an endan-
has been a favored source of meat Verde (the Green Iguana gered species, Dr. Werner has revo-
among native rain-forest inhabi- Foundation). This organization lutionized the concepts of species
tants for thousands of years. sponsors festivals and education preservation and economic devel-
seminars in local communities. opment. This hard-working scien-
Not only do farmers profit These activities promote the tradi- tist has hit upon a solution that
from the sale of iguana meat, they tional appeal of the iguana, increase may encourage farmers throughout
also produce iguana leather and civic pride in the animal, and Central America to “have their
other handicrafts from the lizard. lizards and eat them too.”

Fundación Pro Iguana

Verde

With Dr. Werner’s methods, farmers
can release many iguanas into the
wild and earn a good living. But
convincing farmers to use her meth-
ods hasn’t been easy. According to
Dr. Werner, “Many locals have

̈ Dr. Werner has established an
innovative way to raise the number
of iguanas living in the wild.

What Do You Think?

How does Dr. Werner’s project
protect iguanas and help local
farmers too? Why do you think
that she trains farmers to raise
and value iguanas—what could
her larger goal be? Can you
think of a similar project that
would be suitable for your area?

Chapter 1 Making a Difference 31

2Tools of Environmental Science CHAPTER

1 Scientific Methods
2 Statistics and Models
3 Making Informed Decisions

PRE-READING ACTIVITY

Key-Term
Fold
Before you
read this chap-
ter, create the FoldNote
entitled “Key-Term Fold”
described in the Reading and
Study Skills section of the
Appendix. Write a key term
from the chapter on each tab
of the key-term fold.
Under each tab, write
the definition of the
key term.

This photograph shows a researcher
filming a Weddell seal in Antarctica.
Although scientists often use sophis-
ticated tools in their work, their
most important tools are those they
carry with them—their senses and
their habits of mind.

32 Chapter 2 Tools of Environmental Science

SECTION 1

Scientific Methods

The word science comes from the Latin verb scire, meaning “to Objectives
know.” Indeed, science is full of amazing facts and ideas about
how nature works. But science is not just something you know; it ̈ List and describe the steps of the
is also something you do. This chapter explores how science is experimental method.
done and examines the tools scientists use.
̈ Describe why a good hypothesis is
The Experimental Method not simply a guess.

You have probably heard the phrase, “Today scientists dis- ̈ Describe the two essential parts of
covered…” How do scientists make these discoveries? Scientists a good experiment.
make most of their discoveries using the experimental method.
This method consists of a series of steps that scientists worldwide ̈ Describe how scientists study
use to identify and answer questions. The first step is observing. subjects in which experiments
are not possible.
Observing Science usually begins with observation. Someone
notices, or observes, something and begins to ask questions. An ̈ Explain the importance of curiosity
observation is a piece of information we gather using our senses— and imagination in science.
our sight, hearing, smell, and touch. To extend their senses, scien-
tists often use tools such as rulers, microscopes, and even satellites. Key Terms
For example, a ruler provides our eyes with a standard way to
compare the lengths of different objects. The scientists in Figure 1 observation
are observing the tail length of a tranquilized wolf with the help of hypothesis
a tape measure. Observations can take many forms, including prediction
descriptions, drawings, photographs, and measurements. experiment
variable
Students at Keene High School in New Hampshire have experimental group
observed that dwarf wedge mussels are disappearing from the control group
Ashuelot River, which is located near their school. The students data
have also observed that the river is polluted. These observations correlation
prompted the students to take the next step in the experimental
method—forming hypotheses.

Figure 1 ̈ These scientists are mea-
suring the tail of a tranquilized wolf.
What questions could these observa-
tions help the scientists answer?

Section 1 Scientific Methods 33

QuickLAB Hypothesizing and Predicting Observations give us answers to
questions, but observations almost always lead to more ques-
Hypothesizing and tions. To answer a specific question, a scientist may form a
Predicting hypothesis. A hypothesis (hie PAHTH uh sis) is a testable idea
or explanation that leads to a scientific investigation. A hypothe-
Procedure sis is more than a guess. A good hypothesis follows from what
1. Place a baking tray on a table, you already know and can be tested.

and place a thin book under The Keene High School students observed two trends: that
one end of the tray. the number of dwarf wedge mussels on the Ashuelot River is
2. Place potting soil, sand, and declining over time and that the number of dwarf wedge mussels
schoolyard dirt in three piles at decreases at sites downstream from the first study site. These
the high end of the baking tray. trends are illustrated in Figure 2. Students tested the water in
3. Use a toothpick to poke several three places and found that the farther downstream they went,
holes in a paper cup. the more phosphate the water had. Phosphates are chemicals in
4. Write down a hypothesis to many fertilizers.
explain why soil gets washed
away when it rains. Armed with their observations, the students might make the
5. Based on your hypothesis, pre- following hypothesis: phosphate fertilizer from a lawn is washing
dict which of the three soils will into the river and killing dwarf wedge mussels. To test their
wash away most easily. hypothesis, the students make a prediction, a logical statement
6. Pour water into the cup, and about what will happen if the hypothesis is correct. The students
slowly sprinkle water on the might make the following prediction: mussels will die when
piles. exposed to high levels of phosphate in their water.
Analysis
1. What happened to the differ- It is important that the students’ hypothesis—high levels of
ent soils? phosphate are killing the mussels—can be disproved. If students
2. Revise your hypothesis, if neces- successfully raised mussels in water that has high phosphate levels,
sary, based on your experiment. their hypothesis would be incorrect. Every time a hypothesis is
disproved, the number of possible explanations for an observation
Figure 2 ̈ The diagram below shows is reduced. By eliminating possible explanations a scientist can
the trends observed by the students at zero in on the best explanation with more confidence.
Keene High School. Site 1 is upstream.
Site 3 is downstream. ■✓● Reading Check What is the difference between a hypothesis and a

1998 prediction? (See the Appendix for answers to Reading Checks.)

Site 1 Students found many Site 2 Students found few mussels Site 3 Students found no
mussels in 1998 but fewer in 2000. in 1998 and fewer in 2000. mussels in 1998 or 2000.

2000

34 Chapter 2 Tools of Environmental Science

Experimenting The questions that arise from observations often www.scilinks.org
cannot be answered by making more observations. In this situa-
tion scientists usually perform one or more experiments. An Topic: Experimenting
experiment is a procedure designed to test a hypothesis under in Science
controlled conditions.
Code: HE80556
Experiments should be designed to pinpoint cause-and-effect
relationships. For this reason, good experiments have two essential
characteristics: a single variable is tested, and a control is used. The
variable (VER ee uh buhl) is the factor of interest, which, in our
example, would be the level of phosphate in the water. To test for
one variable, scientists usually study two groups or situations at a
time. The variable being studied is the only difference between the
groups. The group that receives the experimental treatment is called
the experimental group. In our example, the experimental group
would be those mussels that receive phosphate in their water. The
group that does not receive the experimental treatment is called the
control group. In our example, the control group would be those
mussels that do not have phosphate added to their water. If the
mussels in the control group thrive while most of those in the
experimental group die, the experiment’s results support the
hypothesis that phosphates from fertilizer are killing the mussels.

The Experimental
Method In Action
at Keene
High School

Keene High School students ̈ Keene High School students are conducting an experiment
collected mussels (nonendangered to study the effect of phosphate levels on the growth rates of freshwater mussels.
relatives of the dwarf wedge
mussel) and placed equal numbers and having a control group. What would help ensure that the results
of them in two aquariums. They would happen if the aquarium in are not simply due to chance.
ensured that the conditions in the which most of the mussels died had
aquariums were identical—same phosphate in the water and was also CRITICAL THINKING
water temperature, food, hours warmer? The students would not
of light, and so on. The students know if the phosphate or the higher 1. Applying Ideas Why did the
added a measured amount of temperature killed the mussels. students ensure that the conditions
phosphate to the aquarium of the in both aquariums were identical?
experimental group. They added Another key to experimenting in 2. Evaluating Hypothesis How
nothing to the aquarium of the science is replication, or recreating would you change the hypothesis if
control group. the experimental conditions to make mussels died in both aquariums?
sure the results are consistent. In this
A key to the success of an exper- case, using six aquariums—three
iment is changing only one variable control and three experimental—

Section 1 Scientific Methods 35

Figure 3 ̈ This scientist is analyzing Organizing and Analyzing Data Keeping
his data with the help of a computer. careful and accurate records is extremely
important in science. A scientist cannot
Table 1 ̄ rely on experimental results that are based
on sloppy observations or incomplete
Pollutant Concentrations (mg/L) records. The information that a scientist
Site Nitrates Phosphates gathers during an experiment, which is
often in numeric form, is called data.
1 0.3 0.02
2 0.3 0.06 Organizing data into tables and graphic
3 0.1 0.07 illustrations helps scientists analyze the
data and explain the data clearly to others.
Milligrams per liter of water 0.3 Nitrates The scientist in Figure 3 is analyzing data
Phosphates on pesticides in food. Graphs are often
used by scientists to display relationships
0.2 or trends in the data. Graphs are espe-
cially useful for illustrating conclusions
0.1 drawn from an experiment.

0 One common type of graph is called a
Site 1 Site 2 Site 3 bar graph. Bar graphs are useful for com-
paring the data for several things in one graph. Figure 4 shows
Figure 4 ̈ This graph and the table the data in Table 1 in the form of a bar graph. Look at the data
above it compare the concentrations for Site 3 in the bar graph. The data show that the concentration
of phosphates and nitrates in the of phosphates is higher at Site 3 than at Sites 1 and 2, and the
Ashuelot River in 2000. Site 1 is concentration of nitrates is lower than at Sites 1 and 2.
upstream of Sites 2 and 3.
Drawing Conclusions Scientists determine the results of their
experiment by analyzing their data and comparing the outcome
of their experiment with their prediction. Ideally, this comparison
provides scientists with an obvious conclusion. But often the con-
clusion is not obvious. For example, in the mussel experiment,
what if three mussels died in the control tank and five died in the
experimental tank? The students could not be certain that phos-
phate is killing the mussels. Scientists often use mathematical tools
to help them determine whether such differences are meaningful
or are just a coincidence. Scientists also repeat their experiments.

Repeating Experiments Although the results from a single
experiment may seem conclusive, scientists look for a large
amount of supporting evidence before they accept a hypothesis.
The more often an experiment can be repeated with the same
results, in different places and by different people, the more sure
scientists become about the reliability of their conclusions.

Communicating Results Scientists publish their results to share
what they have learned with other scientists. When scientists
think their results are important, they usually publish their find-
ings as a scientific article. A scientific article includes the question
the scientist explored, reasons why the question is important,
background information, a precise description of how the work
was done, the data that were collected, and the scientist’s inter-
pretation of the data.

36 Chapter 2 Tools of Environmental Science

The Correlation Method Connection to Geology

Whenever possible, scientists study questions by using experi- Coral Correlation Some geolo-
ments. But many questions cannot be studied experimentally. gists use an interesting correla-
The question “What was Earth’s climate like 60 million years tion to study records of past
ago?” cannot be studied by performing an experiment because the climates. Certain species of coral
scientists are 60 million years too late. “Does smoking cause lung put down layers of skeleton every
cancer in humans?” cannot be studied experimentally because year and can live for 300 years.
doing experiments that might injure people would be unethical. Coral skeletons contain the ele-
ments strontium, Sr, and calcium,
When using experiments to answer questions is impossible or Ca. In some corals, the ratio of
unethical, scientists test predictions by examining correlations, these elements in a layer of skele-
or associations between two or more events. For example, scien- ton correlates with local sea sur-
tists know that the relative width of a ring on a tree trunk is a face temperature at the time that
good indicator of the amount of rainfall the tree received in a the layer forms. The correlation
given year. Trees produce wide rings in rainy years and narrow between the Sr to Ca ratio and
rings in dry years. Scientists have used this knowledge to investi- the sea temperature provides sci-
gate why the first European settlers at Roanake Island, Virginia entists with one record of how
(often called the Lost Colony) disappeared and why most of the Earth’s climate has changed over
first settlers at Jamestown, Virginia, died. As shown in Figure 5, the centuries.
the rings of older trees on the Virginia coast indicate that the
Lost Colony and the Jamestown Colony were founded during
two of the worst droughts the coast had experienced in centuries.
The scientists concluded that the settlers may have starved
because the famine made it hard to grow food.

Although correlation studies are useful, cor-
relations do not necessarily prove cause-and-
effect relationships between two variables. For
example, the correlation between increasing
phosphate levels and a declining mussel popula-
tion on the Ashuelot River does not prove that
phosphates harm mussels. Scientists become
more sure about their conclusions if they find
the same correlation in different places and as
they eliminate other possible explanations.

Lost Colony Jamestown
Drought
Drought severity index 4 Drought 1606 –1612 Wet Figure 5 ̈ This cross section of a
1587–1589 conditions baldcypress from southeastern
Virginia (above) shows a record of
0 rainfall beginning in 1531. The graph
translates the relative tree ring width
Dry conditions into what is called a drought index,
–4 which allowed scientists to compare
rainfall between different years.
1560 1600 1640 1680
Year Section 1 Scientific Methods 37

Source: Science.

Connection to Biology Scientific Habits of Mind

Discovering Penicillin Alexander Scientists actually approach questions in many different ways.
Fleming discovered penicillin by But good scientists tend to share several key habits of mind, or
accident. Someone left a window ways of approaching and thinking about things.
open near his dishes of bacteria,
and the dishes were infected with Curiosity Good scientists are endlessly curious. Jane Goodall, pic-
spores of fungi. Instead of throw- tured in Figure 6, is an inspiring example. She studied a chimpanzee
ing the dishes away, Fleming troop in Africa for years. She observed the troop so closely that she
looked at them closely and saw came to know the personality and behavior of each member of the
that the bacteria had died on the troop and greatly contributed to our knowledge of that species.
side of a dish where a colony of
green Penicillium mold had started The Habit of Skepticism Good scientists also tend to be skepti-
to grow. If he had not been a cal, which means that they don’t believe everything they are told.
careful observer, penicillin might For example, 19th century doctors were taught that men and
not have been discovered. You women breathe differently—men use the diaphragm (the sheet of
may find Penicillium yourself on muscle below the rib cage) to expand their chest, whereas women
moldy bread. raise their ribs near the top of their chest. Finally, a female doctor
found that women seemed to breathe differently because their
clothes were so tight that their ribs could not move far enough to
pull air into their lungs.

Openness to New Ideas As the example above shows, skepticism
can go hand in hand with being open to new ideas. Good scien-
tists keep an open mind about how the world works.

Figure 6 ̈ Jane Goodall is famous
for her close observations of chim-
panzees—observations fueled in part
by her endless curiosity.

38 Chapter 2

Intellectual Honesty A scientist Scale 100 yards
may be certain that a hypothesis 0 50
is correct before it has been fully
tested. But when an experiment Oxford St. Dean 0 50 100
is repeated, the results may Gt. Marlborough St. Broad St. Pump sites meters
differ from those obtained the
first time. A good scientist will Poland St. St. Deaths from cholera
consider the possibility that the Wardour
new results may be accurate, even
if this means that the hypothesis St.
might be wrong.
King St.
Conduit St.
Brewer St.
Imagination and Creativity Warwick St.
Good scientists are not only Saville Row
open to new ideas but able to
conceive of new ideas themselves. Piccadilly
The ability to see patterns where
others do not, or to imagine Figure 7 ̈ John Snow (bottom)
things that others cannot, allows a created his famous spot map (top),
good scientist to expand the bound- which enabled him to see a pattern
aries of what we know. that no one had noticed before.

An example of an imaginative and
creative scientist is John Snow, shown in Figure 7. Snow was a
physician in London during a cholera epidemic in 1854. Cholera,
a potentially fatal disease, is caused by a bacterium found in water
that is polluted with human waste. Few people had indoor plumb-
ing in 1854. Most people got their water from public pumps; each
pump had its own well. To find the polluted water source, Snow
made a map showing the homes of everyone who died of cholera.
The map also showed the public water pumps. In this example of
a correlation study, he found that more deaths occurred around a
pump in Broad Street than around other pumps in the area.
London authorities ended the cholera epidemic by shutting off the
Broad Street pump. Using observation, imagination, and creativity,
Snow solved an environmental problem and saved lives.

■✓● Reading Check How did drawing a map of London help John Snow

solve the cholera problem in 1854?

S E C T I O N 1 Review

1. Describe the steps of the experimental method. CRITICAL THINKING
5. Analyzing Methods Read the description of experi-
2. Name three scientific habits of mind and explain
their importance. ments. Describe the two essential parts of a good
experiment, and explain their importance.
3. Explain why a hypothesis is not just a guess.
READING SKILLS
4. Explain how scientists try to answer questions that
cannot be tested with experiments. 6. Analyzing Relationships How can a scientist
be both skeptical and open to new ideas at the
same time? Write a one-page story that describes
such a situation. WRITING SKILLS

Section 1 Scientific Methods 39

SECTION 2

Statistics and Models

Objectives Environmental science provides a lot of data that need to be
organized and interpreted before they are useful. Statistics is the
̈ Explain how scientists use statistics. collection and classification of data that are in the form of num-
̈ Explain why the size of a statistical bers. People commonly use the term statistics to describe num-
bers, such as the batting record of a baseball player. Sportswriters
sample is important. also use the methods of statistics to translate a player’s batting
̈ Describe three types of models record over many games into a batting average, which allows
people to easily compare the batting records of different players.
commonly used by scientists.
̈ Explain the relationship between How Scientists Use Statistics

probability and risk. Scientists are also interested in comparing things, but scientists
̈ Explain the importance of concep- use statistics for a wide range of purposes. Scientists rely on and
use statistics to summarize, characterize, analyze, and compare
tual and mathematical models. data. Statistics is actually a branch of mathematics that provides
scientists with important tools for analyzing and understanding
Key Terms their data.

statistics Consider the experiment in which students studied mussels to
mean see if the mussels were harmed by fertilizer in their water. Students
distribution collected data on mussel length and phosphate levels during this
probability experiment. Some mussels in the control group grew more than
sample some mussels in the experimental group, yet some grew less. How
risk could the students turn this data into meaningful numbers?
model
conceptual model Statistics Works with Populations Scientists use statistics to
mathematical model describe statistical populations. A statistical population is a group
of similar things that a scientist is interested in learning about. For
example, the dwarf wedge mussels shown in Figure 8 are part of
the population of all dwarf wedge mussels on the Ashuelot River.

Figure 8 ̈ Students found these
dwarf wedge mussel shells in a
muskrat den. These mussels are part
of the statistical population of all
dwarf wedge mussels on the
Ashuelot River.

40 Chapter 2 Tools of Environmental Science

What Is the Average? Although statistical populations are com- www.scilinks.org
posed of similar individuals, these individuals often have different
characteristics. For example, in the population of students in your Topic: Statistics in
classroom, each student has a different height, weight, and so on. Science

The Keene High School students measured the lengths of Code: HE81452
dwarf wedge mussels in a population, as shown in Figure 8. They
added the lengths of the mussels and then divided by the number Venn Diagram
of mussels. This gave the average length of the mussels, which in Create the
statistical terms is called the mean. The mean is the number Graphic Organizer entitled
obtained by adding the data for a characteristic and dividing this “Venn Diagram” described in the
sum by the number of individuals. The mean provides a single Appendix. Label the circles with
measure for a given characteristic of a population. Scientists can “Statistics” and “Models.” Then,
compare different populations by comparing their means. The fill in the diagram with the charac-
mean length of the mussels in Figure 9 is about 30 mm. teristics that each
way of interpreting
The Distribution The bar graph in Figure 9 shows the lengths of the data shares with
dwarf wedge mussels in a population. The pattern that the bars the other.
create when viewed as a whole is called the distribution. A
distribution is the relative arrangement of the members of a sta-
tistical population. In Figure 9, the lengths of the individuals are
arranged between 15 and 50 mm.

The overall shape of the bars, which rise to form a hump in
the middle of the graph, is also part of the distribution. The line
connecting the tops of the bars in Figure 9 forms the shape of a
bell. The graphs of many characteristics of populations, such as
the heights of people, form bell-shaped curves. A bell-shaped
curve indicates a normal distribution. In a normal distribution,
the data are grouped symmetrically around the mean.

■✓● Reading Check How was the mean length of the dwarf wedge mus-

sel population calculated?

Number of mussels Size Distribution of Dwarf Wedge Mussels Figure 9 ̈ This bar graph shows the
25 distribution of lengths in a population
of dwarf wedge mussels. For example,
20 the second bar from the left indicates
that the population studied contained
15 four mussels between 20 and 25 mm
long.

10

5

0
0 5 10 15 20 25 30 35 40 45 50 55 60

Length (mm)

Section 2 Statistics and Models 41

MATHPRACTICE What Is the Probability? The chance that something will hap-
pen is called probability. For example, if you toss a penny, what
Probability Probability is the probability that it will come up heads? Most people would
is often determined by say “half and half,” and they would be right. The chance of a
observing ratios or patterns. For tossed penny coming up heads is 1⁄2, which can also be expressed
example, imagine that you count as 0.5 or 50%. In fact, probability is usually expressed as a num-
200 pine trees in a forest and ber between 0 and 1 and written as a decimal rather than as a
notice that 40 of those trees have fraction. Suppose the penny comes up heads 7 out of 10 times.
pine cones. What is the probability Does this result prove that the probability of a penny coming up
that the next pine tree you come heads is 0.7? No, it does not. So what is the problem?
across will have pine cones?
The problem is that the sample size—the number of objects
or events sampled—is too small to yield an accurate result. In sta-
tistics, a sample is a group of individuals or events selected to
represent the population. If you toss a penny 10 times, your sam-
ple size is 10. If you continue tossing 1,000 times, you are almost
certain to get about 50% heads and 50% tails. In this example,
the sample is the number of coin tosses you make, while the pop-
ulation is the total number of coin tosses possible. Scientists try
to make sure that the samples they take are large enough to give
an accurate estimate for the whole population.

Figure 10 ̈ Most people are familiar Statistics in Everyday Life
with statistics regarding the weather,
such as the chance, or probability, of You have probably heard, “There is a 50 percent chance of rain
a thunderstorm. today.” Figure 10 shows an example of a natural event that we often
associate with probability—a thunderstorm. You encounter statistics
often and use them more than you may think. People are constantly
trying to determine the chance of something happening. A guess or
gut instinct is probably just an unconscious sense of probability.

Understanding the News The news contains statistics every day,
even if they are not obvious. For example, a reporter may say,

“A study shows that forest fires
increased air pollution in the city last
year.” We could ask many statistical
questions about this news item. We
might first ask what the average
amount of air pollution in the city is.
We could gather data on air pollution
levels over the past 20 years and graph
them. Then we could calculate the
mean, and ask ourselves how different
last year’s data are from the average.
We might graph the data and look at
the distribution. Do this year’s pollu-
tion levels seem unusually high com-
pared to levels in other years?
Recognizing and paying attention to
statistics will make you a better con-
sumer of information, including infor-
mation about the environment.

42 Chapter 2 Tools of Environmental Science

Figure 11 ̈ The graph below shows
the sources of oil that pollute the
ocean. The photo at left shows an oil
spill off the coast of Galveston, Texas.
Big oil spills are a relatively minor
source of oil pollution.

Runoff from land
51.4%

Routine ship
maintenance

19.4%

Big spills

5.2%

Natural seeps Air pollution
8.8% Offshore 13.0%

drilling

2.2%

Thinking About Risk In scientific terms, risk is the probability Connection to Law
of an unwanted outcome. For example, if you have a 1 in 4
chance of failing a class, the risk of failing is 1⁄4, or 0.25. Oil Tankers The Oil Pollution Act
Figure 11 shows a well-publicized environmental problem—oil of 1990 was a response to a huge
spills. But as you can see in the pie graph, the risk of pollution oil spill from an oil tanker, the
from large oil spills is much smaller than the risk of oil pollu- Exxon Valdez, in Alaska in 1989.
tion from everyday sources. The controversial bill had been
debated for 14 years; it passed
The most important risk we consider is the risk of death. swiftly in the aftermath of the dis-
Most people overestimate the risk of dying from sensational aster. Under the law, all oil
causes, such as terrorism, and underestimate the risk from com- tankers operating in United States
mon causes, such as smoking. Likewise, most citizens over- waters must be protected with
estimate the risk of sensational environmental problems and double hulls by 2015.
underestimate the risk of ordinary ones, as shown in Table 2.
Section 2 Statistics and Models 43
Table 2 ̄

Perceptions of Risk by Experts and Ordinary Citizens

High risk Low risk

Experts ozone depletion; oil spills;
Citizens global climate change radioactive materials;
water pollution
ozone depletion;
radioactive waste; global climate change;
oil spills water pollution

Source: U.S. Environmental Protection Agency.

Figure 12 ̈ This plastic model of a Models
DNA molecule is an example of a
physical model. You are probably already familiar with models. Museums have
models of ships, dinosaurs, and atoms. Architects build models of
Geofact buildings. Even crash-test dummies are models. Models are repre-
sentations of objects or systems. Although people usually think of
Fossil-Fuel Deposits Fossil fuels, models as things they can touch, scientists use several different
such as coal and oil, are often types of models to help them learn about our environment.
buried deep underground in
particular rock formations. We Physical Models All of the models mentioned above are physical
find fossil fuels by drilling for models. Physical models are three-dimensional models you can
rocks that indicate the presence touch. Their most important feature is that they closely resemble
of fossil fuels and then we make the object or system they represent, although they may be larger
models of where the coal or oil or smaller.
is likely to be found.
One of the most famous physical models was used to discover
Figure 13 ̈ This map of the Denver, the structure of DNA. The two scientists who built the structural
Colorado, area is an example of a model of DNA knew information about the size, shape, and
graphical model. bonding qualities of the subunits of DNA. With this knowledge,
the scientists created model pieces that resembled the subunits
and the bonds between them. These pieces helped them figure out
the possible structures of DNA. Discovering the structure of
DNA furthered other research that helped scientists understand
how DNA replicates in a living cell. Figure 12 shows a modern
model of a DNA molecule. The most useful models teach scien-
tists something new and help to further other discoveries.

Graphical Models Maps and charts are the most common exam-
ples of graphical models. Showing someone a road map is easier
than telling him or her how to get somewhere. An example of a
graphical model is the map of the Denver, Colorado, area in
Figure 13. Scientists use graphical models to show things such as
the positions of the stars, the amount of forest cover in a given
area, and the depth of water in a river or along a coast.

Gill

Estes Glen Boyd Lake S.P. Univ. of
Park Haven 34
14 ROUTT Willow Creek ROCKY N. Colo.
NATL. FOR. Pass
Loveland Greeley40 9,621 Fall 402 Evans Kersey
BouldLeorngmontColorado
N 34 MOUNTAIN 7 36 Campion 60 Milliken Garden
S 56 La City
0 5 10 Mi Berthoud Johnstown Salle
Grand Longs Pk. Pinewood Sprs. S
125 Lake 14,255 ROOSEVELT 287 87 60 Gilcrest Box Elder Cr.
W E 25
Meeker Park NATL. Lyons Mead
0 5 10 Km
NATL. PARK FOR. Platteville
ARAPAHO 66
NATL. FOR. Ft. Vasquez
GRAND Lake Allenspark 7
Granby Ione
Hot Sulphur Raymond Frederick Fort 76
Kremmling Springs Lupton 6
Jamestown Niwot
40
Granby ARAPAHO Ward B O U L D E R 119 52 Dacono 52
N.R.A.
Hudson
Parshall 7 Lafayette 85 Brighton
Nederland 72 Louisville 7
Williams Eldora
Fork Res. Tabernash 119

ILLIAMS FORK MTS. BlueARAPAHO Fraser Rollinsville Pinecliffe 36 Broomfield Barr S.P. ADA MS
W Lake
N.F. Winter Park 72 128 Thornton E-470
GORE RANGE E. Portal Denver
Berthoud Pass 40 Commerce Intl. Arpt.
11,315 GILPIN Westminster
City
9 Central City Arvada ROCKY MTN. ARSENAL N.W.A.
Dumont
Ute 119 Golden Watkins Manila 36 B
SUMMIT Pass Empire
9,524 6

Colo. Ski Mus. & Silver Plume 103 40 DENVER Aurora
Lakewood
Hall of Fame Georgetown 70
Bakerville Englewood E-470
Vail Silverthorne 6 285 470 Littleton
DenverAvon
103 70
ARAPAHOE
Loveland Mt. Evergreen
Pass Evans
Dillon 11,990 14,264 5 CLEAR
Keystone
Frisco CREEK

Vail Pass
10,666
EAGLE Gilman 70 Dillon Res.Montezuma Guanella Pass 11,669 Conifer JEFFERSON 121 85 Parker
Kassler
Red Copper Mtn. Grant Louviers 87 83 The ELBERT
Cliff Breckenridge Singleton Sedalia Pinery

24 91 285 Shawnee Pine FoxtonRoxboroSug.Ph. Castle
P A R K Bailey
Fremont Blue River 105 Rock
Pass 9 South 86
11,318 Jefferson Buffalo Creek Platte 67 Elizabeth

44 Chapter 2 Tools of Environmental Science

Conceptual Models A conceptual model is a verbal or graphical FIELD ACTIVITY
explanation of how a system works or is organized. A flow-chart
diagram is an example of a type of conceptual model. A flow- Conceptual Model Accompany
chart uses boxes linked by arrows to illustrate what a system con- your class outdoors. Observe
tains and how those contents are organized. your surroundings, and write
down observations about what
Consider this example. Suppose that a scientist wants to you see. In your Ecolog, draw a
know how mercury, a poisonous metal, moves through the envi- conceptual model of something
ronment to reach people after the mercury is released from burn- you observe. Your model should
ing coal. The scientist would use an understanding of mercury in represent a system with compo-
the environment to build a conceptual model, as shown in Figure nents that interact, such as a
14. Scientists often create such diagrams to help them understand small community of organisms.
how a system works—what components the system contains,
how they are arranged, and how they affect one another. www.scilinks.org

Conceptual models are not always diagrams. They can also Topic: Using Models
be verbal descriptions or even drawings of how something Code: HE81588
works or is put together. For example, the model of an atom as
a large ball circled by smaller balls is a conceptual model of the
structure of an atom. As this example shows, an actual model
can be more than one type. An atomic model made of plastic
balls is both a conceptual model and a physical model.

■✓● Reading Check How does building a conceptual model help

scientists in their work?

Figure 14 ̈ This conceptual model
shows how mercury released from
burning coal could end up reaching
people, where it could cause
poisoning.

Section 2 Statistics and Models 45

Figure 15 ̈ This is a satellite Mathematical Models A mathematical model is one or more
image of the San Francisco Bay Area. equations that represents the way a system or process works.
Scientists use mathematical models You can represent many common situations using math models.
to understand the terrain from the
way objects on the surface reflect For example, suppose that the grapes in a fruit basket at
light. In this image, healthy vegeta- home are getting moldy. You notice that every day the mold cov-
tion is red. ers two more grapes. Here is a mathematical model for the num-
ber of moldy grapes on Tuesday:

MTue ҃ MMon ѿ 2, where M ҃ number of moldy grapes

Mathematical models are especially useful in cases with many
variables, such as the many things that affect the weather.

Because mathematical models use numbers and equations,
people may think the models are always right. But weather
models, for example, sometimes predict rain on dry days. In fact,
people are the ones who interpret data and write the equations.

If the data or the equations are
wrong, the model will not be real-
istic and so will provide incorrect
information. Like all models,
mathematical models are only as
good as the data that went into
building them.

People may think of math-
ematical models as being confined
to blackboards and paper, but sci-
entists can use the models to cre-
ate amazing, useful images. Look
at the image of the San Francisco
Bay Area in Figure 15. This is a
“false color” digital satellite
image. The satellite measures
energy reflected from the Earth’s
surface. Scientists use mathemati-
cal models to relate the amount of
energy reflected from objects to
the objects’ physical condition.

S E C T I O N 2 Review

1. Explain why sample size is important in determining CRITICAL THINKING
probability. 4. Analyzing Relationships Explain the relationship

2. Explain what “the mean number of weeds in three between probability and risk.
plots of land” means.
5. Applying Ideas Write a paragraph that uses exam-
3. Describe three types of models used by scientists. ples to show how scientists use statistics. WRITING SKILLS

6. Evaluating Ideas Why are conceptual and math-
ematical models especially powerful?

46 Chapter 2 Tools of Environmental Science

SECTION 3

Making Informed Decisions

Scientific research is an essential first step to solve environmental Objectives
problems. However, many other factors must also be considered.
How will the proposed solution affect people’s lives? How much ̈ Describe three values that people
will it cost? Is the solution ethical? Questions like these require consider when making decisions
an examination of values, which are principles or standards we about the environment.
consider important. What values should influence decisions that
affect the environment? Table 3 lists some values that often affect ̈ Describe the four steps in a
environmental decisions. You might think of others as well. simple environmental decision-
making model.
An Environmental Decision-Making Model
̈ Compare the short-term and
Forming an opinion about an environmental issue is often difficult long-term consequences of two
and may seem overwhelming. It helps to have a systematic way of decisions regarding a hypothetical
analyzing the issues and deciding what is important. One way to environmental issue.
guide yourself through this process is to use a decision-making
model. A decision-making model is a conceptual model that pro- Key Terms
vides a systematic process for making decisions.
value
Figure 16 shows one possible decision-making model. The decision-making model
first step of the model is to gather information. In addition to
watching news reports and reading about environmental issues, Gather information
you should listen to well-informed people on all sides of an issue.
Then consider which values apply to the issue. Explore the conse- Consider values
quences of each option. Finally, evaluate all of the information to
make a decision. Explore consequences

■✓● Reading Check Why is a decision-making model helpful for making Make a decision

environmental decisions? Figure 16 ̈ The diagram above
shows a simple decision-making
Table 3 ̄ model.

Values That Affect Environmental Decision Making

Value Definition

Aesthetic what is beautiful or pleasing
Economic the gain or loss of money or jobs
Environmental the protection of natural resources
Educational the accumulation and sharing of knowledge
Ethical/moral what is right or wrong
Health the maintenance of human health
Recreational human leisure activities
Scientific understanding of the natural world
Social/cultural the maintenance of human communities
and their values and traditions

Section 3 Making Informed Decisions 47

Figure 17 ̈ The map (above) A Hypothetical Situation
shows the proposed nature
preserve, which would be Consider the following hypothetical example. In the town of
home to warblers like the Pleasanton, in Valley County, biologists from the local college
one pictured (right). have been studying the golden-cheeked warbler, shown in
Figure 17. The warblers have already disappeared from most
areas around the state, and the warbler population is declining
in Valley County. The biologists warn county officials that if the
officials do not take action, the state fish and wildlife service
may list the bird as an endangered species.

Pleasanton is growing rapidly, and much
of the new development is occurring outside

the city limits. This development is destroy-
ing warbler habitat. Valley County
already has strict environmental controls
on building, but these controls do not
prevent the clearing of land.
Several groups join together to pro-
pose that the county buy several hundred

acres of land where the birds are known to

Saving the Everglades: Making
Informed Decisions

The Florida Everglades is an enor- Scientists have shown that what ̈ The roseate spoonbill is a col-
mous, shallow freshwater marsh. remains of the Everglades is dying. Its orful resident of the Everglades.
The water in the Everglades slowly islands and mangrove swamps are
flows from Lake Okeechobee to vanishing, its water is polluted with
Florida Bay. Much of the marsh is fertilizer from farms, and its wading-
filled with sawgrass, mangroves, bird colonies are much smaller than
and other water-loving plants. It is before. These effects have economic
also home to wildlife, from 40 consequences. Because much of the
species of fish to panthers, alliga- Everglades’ water has been diverted
tors, and wading birds such as from Florida Bay into the Atlantic
herons and roseate spoonbills. Ocean, the towns of southeast
Florida are running out of fresh water
In the 1880s, marshlands were and much of the marine life in
considered wastelands. Developers Florida Bay has died.
began to drain the Everglades. They
replaced marsh with houses and In the 1990s, a commission
sugarcane fields. Between 1940 and reported that the destruction of the
1971, the Army Corps of Engineers Everglades had jeopardized the
built dikes, canals, and pumping state’s tourism industry, farming, and
stations that drained even more the economic future of south Florida.
water. The Corps also straightened The solution was obvious—undo
the Kissimmee River, which runs the water diversion dikes and dams
into Lake Okeechobee. and restore water to the Everglades.

48 Chapter 2 Tools of Environmental Science

breed and save that land as a nature preserve. The groups also Ecofact
propose limiting development on land surrounding the preserve.
The group obtains enough signatures on a petition to put the The Everglades There are 112
issue to a vote, and the public begins to discuss the proposal. threatened or endangered plant
and animal species in the Florida
Some people who own property within the proposed pre- Everglades, according to the U.S.
serve oppose the plan. These property owners have an economic Fish & Wildlife Service.
interest in this discussion. They believe that they will lose
money if they are forced to sell their land to the county instead www.scilinks.org
of developing it.
Topic: Environmental
Other landowners support the plan. They fear that without Decision Making
the preserve the warbler may be placed on the state’s endan- Code: HE80525
gered species list. If the bird is listed as endangered, the state
will impose a plan to protect the bird that will require even
stricter limits on land development. People who have land near
the proposed preserve think their land will become more valu-
able. Many residents of Pleasanton look forward to hiking and
camping in the proposed preserve. Other residents do not like
the idea of more government regulations on how private prop-
erty can be used.

plan than without it. Already Florida
has restored 7 miles of the
Kissimmee River to its original path.
Native plants are absorbing some
of the pollution that has killed an
estimated $200 million worth of
fish and wildfowl. The Everglades
Restoration Plan is not perfect, but
the process of creating and approv-
ing it shows how science and
thoughtful negotiation can help solve
complex environmental problems.

̈ The Everglades can be thought of as a shallow, slow-moving river CRITICAL THINKING
that empties into Florida Bay.
1. Analyzing Processes Explain
In 2000, the $7.8 billion Everglades first people were afraid to break up why it was so difficult for people to
Restoration Plan was signed into law. into committees for fear that other agree on how to restore the
The plan was put together by groups people would make deals behind Everglades.
that had been fighting over the their backs. The director instituted
Everglades for decades: environmen- social gatherings, and the members 2. Analyzing Relationships
talists, politicians, farmers, tourism got to know and trust each other. If your county decided to build a
advocates, and developers. Over the landfill, do you think the decision-
course of 5 years, members from the In the end, no one was com- making process would resemble the
groups met and crafted a plan. At pletely satisfied, but all agreed that Everglades example?
they would be better off with the

Section 3 Making Informed Decisions 49

Warbler PopulationNumber of breeding pairs How to Use the Decision-Making Model
in the Pleasanton Area
50 The hypothetical situation in Pleasanton can be used to illustrate
how to use the decision-making model. Michael Price is a voter in
40 Valley County who will vote on whether the county should create
a nature preserve to protect the golden-cheeked warbler. The
30 steps Michael took to make his decision about the proposal are
outlined below.
20
Gather Information Michael studied the warbler issue thor-
10 oughly by watching local news reports, reading the newspaper,
learning more about golden-cheeked warblers from various Web
0 sites, and attending forums where the issues were discussed. An
1992 1994 1996 1998 2000 2002 example of scientific information that Michael considered
includes the graph of warbler population decline in Figure 18.
Year Several of the arguments on both sides made sense to him.

Figure 18 ̈ The population of Consider Values Michael made a table similar to Table 4 to
golden-cheeked warblers in the clarify his thoughts. The values listed are environmental, eco-
Pleasanton area has declined in nomic, and recreational. Someone else might have thought other
recent years. values were more important to consider.

Table 4 ̄ Should Valley County Set Aside a Nature Preserve?

Positive Environmental Economic Recreational
short-term
consequences Habitat destruction in Landowners whose property was bought by Parts of the preserve are
the nature preserve the county receive a payment for their land. made available
area is slowed or immediately for hiking
stopped. Property outside the preserve area can be and picnicking.
developed with fewer restrictions.

Negative Environmental Property owners inside the preserve area do Michael could not think
short-term controls are made
consequences less strict in parts of not make as much money as if they had of any negative short-
the county outside
the preserve area. developed their land. term consequences.

Taxpayers must pay higher taxes to buy
preserve land.

Positive The population of Property near the preserve increases in Large areas of the
long-term warblers increases, value because it is near a natural area. preserve are available for
consequences and the bird does not hiking and picnicking.
become endangered. Businesses move to Valley County because of
its beauty and recreational opportunities, Landowners near the
Other species of which results in job growth. preserve may develop
organisms are also campgrounds with bike
protected. The warbler is not listed as endangered, trails, swimming, and
which avoids stricter controls on land use. fishing available on land
An entire habitat is adjacent to the
preserved. preserve.

Negative Other habitat outside Taxpayers must continue to pay for State officials might
long-term the preserve may be maintaining the preserve. restrict some
consequences damaged by recreational activities on
overdevelopment. Taxpayers lose the tax revenue that this land private land within the
would have provided if it was developed. preserve.

50 Chapter 2 Tools of Environmental Science

Explore Consequences Michael decided that in the short term Figure 19 ̈ Land set aside for a
the positive and negative consequences listed in his table were nature preserve can benefit people as
almost equally balanced. He saw that some people would suffer well as wildlife.
financially from the plan, but others would benefit. Taxpayers
would have to pay for the preserve, but all the residents would
have access to land that was previously off-limits because it was
privately owned. Some parts of the county would have more pro-
tection from development, and some would have less.

The long-term consequences of the plan helped Michael make
his decision. He realized that environmental values were an
important factor. The idea of a bird becoming extinct distressed
him. Also, protecting warbler habitat now would cost
less than doing it later under a state-imposed plan.

Michael considered that there were long-term
benefits to add to the analysis as well. He had read
that property values were rising more rapidly in
counties with land for recreation. He found that peo-
ple would pay more to live in counties that have open
spaces. Michael had found that Valley County had
very little preserved land. He thought that creating
the preserve would bring the county long-term eco-
nomic benefits. He also highly valued the aesthetic
and recreational benefits a preserve would offer, such
as the walking trail in Figure 19.

Make A Decision Michael chose to vote for the nature
preserve. Other people who looked at the same table of
pros and cons might have voted differently. If you lived
in Valley County, how would you have voted?

As you learn about issues affecting the environ-
ment, both in this course and in the future, use this
decision-making model as a starting point to making
your decisions. Make sure to consider your values,
weigh pros and cons, and keep in mind both the short-
term and long-term consequences of your decision.

■✓● Reading Check How did considering long-term conse-

quences help Michael make a decision about creating a

nature preserve in Valley County?

S E C T I O N 3 Review

1. Explain the importance of each of the four steps in a CRITICAL THINKING
simple decision-making model. 4. Making Decisions Pick one of the situations you

2. List and define three possible values to consider described in question 3. Make a decision-making table
when making environmental decisions. that shows the positive and negative consequences of
either of two possible decisions.
3. Describe in a short paragraph examples of two
situations in which environmental values come into 5. Analyzing Ideas Suggest how to make the deci-
conflict with other values. WRITING SKILLS sion-making model presented here more powerful.

Section 3 Making Informed Decisions 51

2C H A P T E R Highlights

1 Scientific Methods Key Terms Main Ideas

observation, 33 ̈ Science is a process by which we learn about
hypothesis, 34 the world around us. Science progresses mainly
prediction, 34 by the experimental method.
experiment, 35
variable, 35 ̈ The experimental method involves making
experimental observations, forming a hypothesis, performing
an experiment, interpreting data, and commu-
group, 35 nicating results.
control group, 35
data, 36 ̈ In cases in which experiments are impossible,
correlation, 37 scientists look for correlations between differ-
ent phenomena.

̈ Good scientists are curious, creative, honest,
skeptical, and open to new ideas.

2 Statistics and Models statistics, 40 ̈ Scientists use statistics to classify, organize,
mean, 41 and interpret data.
distribution, 41
probability, 42 ̈ Measures such as means and probabilities
sample, 42 are used to describe populations and events.
risk, 43
model, 44 ̈ Statistics provides a powerful tool for evalu-
conceptual model, 45 ating information about the environment.
mathematical
̈ Scientists use models, including conceptual
model, 46 and mathematical models, to understand the
systems they study.

3 Making Informed Decisions value, 47 ̈ Making environmental decisions involves
gathering information, considering values, and
decision-making exploring consequences.
model, 47
̈ Decisions about the environment should be
made thoughtfully. Using a decision-making
model will provide you with a systematic
process for making knowledgeable decisions.

̈ Making a table that lists positive and nega-
tive short-term and long-term consequences
will help you recognize and weigh your values
about an environmental decision.

52 Chapter 2 Highlights

2C H A P T E R Review

Using Key Terms 13. In a population, characteristics such as size
will often be clustered around the
Use each of the following terms in a separate a. sample.
sentence. b. mean.
c. distribution.
1. experiment d. collection.
2. correlation
3. model 14. Models used by scientists include
4. distribution a. conceptual models.
5. values b. variable models.
For each pair of terms, explain how the meanings c. physical models.
of the terms differ. d. Both (a) and (c)
6. hypothesis and prediction
7. risk and probability 15. Reading scientific reports is an example of
8. distribution and population a. assessing risk.
9. sample and population b. considering values.
c. gathering information.
STUDY TIP d. exploring consequences.

Imagining Examples To understand how key 16. A conceptual model represents a way of
terms apply to actual examples, work with a part- thinking about
ner and take turns describing an environmental a. relationships.
problem and explaining how the key terms relate b. variables.
to the problem. c. data.
d. positions.
Understanding Key Ideas
17. In an experiment, the experimental treatment
10. Scientists form _______ hypotheses to differs from the control treatment only in the
answer questions. _______ being studied.
a. accurate a. experiment
b. short b. variable
c. mathematical c. hypothesis
d. testable d. data

11. Risk is the _______ of a negative outcome. 18. To fully understand a complex environmen-
a. sample tal issue, you may need to consider
b. statistic a. economics.
c. probability b. values.
d. event c. scientific information.
d. All of the above
12. If the results of your experiment do not sup-
port your hypothesis, you should 19. Scientists _______ experiments to make sure
a. publish your results anyway. the results are meaningful.
b. consider the results abnormal and continue a. perform
working. b. repeat
c. find a way to rationalize your results. c. conclude
d. try another method. d. communicate

Chapter 2 Review 53

2C H A P T E R Review

Short Answer Concept Mapping ?
??
20. Explain the statement, “A good scientist is
one who asks the right questions.” 28. Use the following terms to create a concept
map: control group, experiment, experimen-
21. Explain the role of a control group in a scien- tal group, prediction, data, observations,
tific experiment. conclusions, and hypothesis.

22. How are statistics helpful for evaluating infor- Critical Thinking
mation about the environment?
29. Drawing Conclusions What does a scientist
23. Explain why environmental scientists use mean by the statement, “There is an 80
mathematical models. percent probability that a tornado will hit
this area within the next 10 years”?
24. How does making a table help you evaluate
the values and concerns you have when 30. Making Inferences How does a map of
making a decision? Denver allow you to navigate around the city?

Interpreting Graphics 31. Evaluating Assumptions Are complicated
models always more accurate? Write a para-
The graph below shows the change in size of a graph that uses examples to explain your
shoreline alligator population over time. Use the answer. WRITING SKILLS
graph to answer questions 25–27.
32. Interpreting Statistics Explain what the
25. What happened to the density of alligators following statement proves: “We sampled
between 1986 and 1988? pet owners and found that three out of five
surveyed own dogs and two out of five
26. What happened to the trend in the alligator surveyed own cats.”
concentration between 1994 and 1998?
Cross-Disciplinary Connection
27. How many times greater was the alligator
population in 1986 than it was in 2000? 33. Language Arts The word serendipity, which
means “luck in finding something acciden-
20 tally,” came from a Persian fairy tale called
The Three Princes of Serendip. In the story,
Alligators per kilometer of shoreline 16 each of the princes discovers something by
accident. Research and write a short report
12 on a serendipitous discovery about the envi-
ronment. WRITING SKILLS

8 Portfolio Project

4 34. Make a Poster Choose an environmental
issue in your area. You can choose a real-life
0 1990 1995 2000 problem that you have heard about on the
1985 news, such as improving the sewage system or
building a new landfill, or you can choose a
Year project that you think should be considered.
Research the issue at your school or local
library. Prepare a poster listing the groups of
people likely to be involved in the decision
and the factors that may be taken into con-
sideration, including economic, social, and
environmental factors.

54 Chapter 2 Review

MATH SKILLS READING SKILLS

This table shows the results of an experiment Read the passage below, and then answer
that tested the hypothesis that butterflies are the questions that follow.
attracted to some substances but not to others.
Twenty-four trays containing four substances Jane and Jim observed a group of male but-
were placed in random order on a sandbank to terflies by the roadside. Jane said that this
see if butterflies landed on the trays. The number behavior was called puddling and that the
of butterflies that landed on each type of tray butterflies were counting each other to see if
and stayed for more than 5 min during a 2 h there was room to set up a territory in the
period was recorded in the table. Use the data in area. Jim said he did not think butterflies
the table below to answer questions 35–36. could count each other and suggested the but-
terflies were feeding on nitrogen in the sand.
Butterfly Feeding Preferences Jane agreed that the butterflies appeared to be
feeding, but she said that they may not be
Sugar Nitrogen Salt feeding on nitrogen, because female butterflies
need more nitrogen than males.
solution solution Water solution
Jim and Jane decided to perform some
Number of 5 87 7 403 experiments on the butterflies. They put out
butterflies trays full of sand in an area where butterflies
attracted had been seen. Two trays contained only
sand. Two contained sand and water, two
35. Evaluating Data Do the results in the table contained sand and a salt solution, and two
show that butterflies are attracted to salt contained sand and a solution containing
solution but not any other substance? Why nitrogen. Butterflies came to all the trays, but
or why not? What other data would you they stayed for more than 1 min only at the
like to see to help you evaluate the results trays that contained the salt solution.
of this experiment?
1. Which of the following statements is a
36. Analyzing Data Are there any controls testable hypothesis about the experiment?
shown in this table? a. Male butterflies mate with female
butterflies.
WRITING SKILLS b. Salt is a compound and nitrogen is
an element.
37. Communicating Main Ideas How is the c. Butterflies are never seen in groups
experimental method an important scientific except on sandy surfaces.
tool? d. Butterflies are attracted to salt.

38. Writing Persuasively Write a letter to the 2. Which of the following conclusions is
editor of your local paper outlining your supported by the observations Jane and
opinion on a local environmental issue. Jim made?
a. Male butterflies can count each other.
b. The butterflies were probably feeding
on nitrogen in the sand.
c. The butterflies were probably feeding
on salts in the sand.
d. Female butterflies need less nitrogen
than male butterflies.

Chapter 2 Review 55

2C H A P T E R Standardized Test Prep

Understanding Concepts Reading Skills

Directions (1–4): For each question, write on a Directions (7–9): Read the passage below. Then
separate sheet of paper the letter of the correct answer the questions.
answer.
We use statistics everyday. Weather experts
1 How would a scientist categorize a testable report the forecast in terms of probabilities,
such as “There is a 50 percent chance of rain
explanation for an observation? today.” People are constantly guessing the
A. a correlation possibility that something will or will not
B. an experiment happen. A guess is one of the ways we express
C. a hypothesis probability.
D. a prediction
In scientific terms, risk is the probability
2 What happens when an observation is of an unwanted outcome. Most people over-
estimate the risk of dying from sensational
submitted for peer review? causes, such as terrorism, and underestimate
F. The article is proofread before it is the risk from common causes such as smoking.
Likewise, most citizens overestimate the risk of
published. sensational environmental problems such as oil
G. A professor gives a lecture based on a spills, and underestimate the risk of ordinary
ones, like ozone depletion. However, when
published article. decisions must be made on proposals affecting
H. The results are looked at closely by other the environment, it is important that all the
benefits and risks of the possible action are
scientific experts. calculated.
I. Information on the experimental design
7 Assess which of the following experts
is included in published works.
would perceive as having the highest risk.
3 Which of the following is an example of a A. the threat of global climate change
B. the radioactivity from the waste of a
scientist’s physical model?
A. a crash-test dummy for a car company nuclear power plant
B. a diagram of the structure of an atom C. the possibility of a tidal wave reaching a
C. a map of Denver, Colorado
D. a satellite image of South America highly populated land mass
D. the danger of widespread water pollution
4 What attribute of a skeptic would
8 How would a scientist define the term risk?
contribute to a good scientific mind?
F. willingness to travel F. the likelihood of something good
G. empathetic nature G. a chance event
H. desire to conduct experiments H. the probability of an unwanted outcome
I. continual questioning of observations I. a benefit that is overestimated

Directions (5–6): For each question, write a short 9 How could a decision-making model be
response.
helpful for estimating the benefits and risks
5 A penny is tossed and comes up heads 7 of a proposal?
A. It would eliminate uncertainty.
out of 10 times. Is the probability that it B. It would create a digital image.
will be heads on the next toss 70%? Why C. It would predict the outcome of the
or why not?
decision.
6 A mean is the number obtained by adding D. It would allow consideration of all the

up the data for a given characteristic of a variables.
statistical population, and dividing the sum
by the total number of individuals in the
given population. Why do scientists calcu-
late the mean of a statistical population?

56 Chapter 2 Standardized Test Prep

Interpreting Graphics

Directions (10–13): For each question below, record the correct answer on
a separate sheet of paper.
The bar graph below shows the distribution of lengths in a population of
dwarf wedge mussels. Use this graph to answer questions 10 through 13.

Size Distribution of Dwarf Wedge Mussels

25

20

Number of mussels 15

10

5

0
0 5 10 15 20 25 30 35 40 45 50 55 60
Length (mm)

0 What type of distribution does this bell-shaped curve depict?

F. asymmetric
G. correlative
H. normal
I. random

q How many mussels are less than 25 mm in length?

A. 6
B. 9
C. 12
D. 15

w Determine the total size of this statistical population of dwarf wedge Test

mussels. Probability is the
F. 60 chance of an outcome
G. 70 occurring. The highest
H. 80 probability occurs in
I. 90 the group with the
largest number of
e What is the most likely size predictable for a mussel randomly drawn individuals.

from this population?
A. 15–20 mm
B. 25–30 mm
C. 30–35 mm
D. 40–45 mm

Chapter 2 Standardized Test Prep 57

2C H A P T E R Skills Practice Lab: OBSERVATION

Objectives Scientific Investigations

̈ USING SCIENTIFIC METHODS Formulate A scientist considers all the factors that might be responsible for
a hypothesis about the relationship what he or she observes. Factors that can vary and that can be
between temperature and fermen- measured are called variables. The variable that you experimentally
tation by yeast. manipulate is the independent variable. The variable that you
think will respond to this manipulation is the dependent variable.
̈ USING SCIENTIFIC METHODS Test your
hypothesis. You can practice the scientific method as it relates to everyday
observations, such as the observation that bread dough rises
̈ Analyze your data. when it is baked. According to a bread recipe, you dissolve a
̈ Explain whether your data support package of yeast in warm water and add flour, corn syrup, salt,
and oil. Yeast is a microorganism that plays an important role in
or refute your hypothesis. making bread. Yeast obtains energy by converting sugar to alco-
hol and carbon dioxide gas in a process called fermentation. The
Materials carbon dioxide forms bubbles, which make the bread dough rise.
But what role, if any, does temperature play in this process? In
beakers, 100 mL (3) this investigation, you will work as part of a team to try to
beakers, 400 mL (3) answer these questions. Together, you will form a hypothesis and
clock conduct an experiment that tests your hypothesis.
delivery tubes, rubber or
Procedure
plastic (3)
graph paper 1. Restate the question relating temperature to fermentation in
ice cubes yeast as a hypothesis.
solution of yeast, corn syrup,
2. Set up three test tubes containing yeast, water, and corn
and water syrup stoppered with a gas-delivery tube. Label the test
stoppers, no. 2, one-hole (3) tubes “A”, “B”, and “C”. Place each test tube in a water
test tubes, 20 mm ҂ 200 mm (3) bath of different temperature. Place tube A in a water bath
thermometer cooled by a few ice cubes, place tube B in room-tempera-
ture water, and place tube C in a warm water bath.
̈ Step 3 Carbon dioxide bubbles
will be released from the delivery tube. 3. Allow the apparatus to sit for 5 min.
Then place the open end of the delivery
tube under water and begin to collect
data on gas production. For the next
10 min, count the number of gas bub-
bles released from each tube, and
record your data in the table on the
next page.

4. Prepare a graph of data by placing time
on the x-axis and the total number of gas
bubbles released on the y-axis. Plot three
curves on the same graph, and label each
with the temperature you recorded for
each test tube. Compare your graph with
that of three other teams before handing
in your report.

58 Chapter 2 Skills Practice Lab

Carbon Dioxide Bubbles Released by Yeast

Time (min) 1 2 3 4 5 6 7 8 9 10

Tube A:_____ DO NOT WRITE IN THIS BOOK
Tube B:_____
Tube C:_____

Analysis ̈ Recording Data Count the
number of bubbles produced under
1. Classifying Data Which set of conditions is most similar to each experimental condition and
the conditions for the bread dough in the recipe? Why were record the data in a table.
two other conditions used in this experiment?

2. Classifying Data What was the independent variable in this
experiment? Explain your answer.

3. Classifying Data What was the dependent variable in this
experiment? Explain your answer.

Conclusions

4. Drawing Conclusions Write a conclusion for this exper-
iment. Describe how the independent and dependent
variables are related. Tell how the data supports your
conclusion.

5. Evaluating Results What does temperature have to do
with making bread dough rise?

6. Evaluating Methods Why did you compare your
results with those of other teams before writing your
conclusions?

7. Applying Conclusions Science is not just something
you know but also something you do. Explain this
statement in light of what you have learned in this
investigation.

Extension

1. Designing Experiments Formulate a new hypothesis
about the effect of different types of sugar on carbon
dioxide production by yeast. Test your new hypothesis
under controlled conditions. Did your results support
your hypothesis? Research the types of sugar you used,
and write a short explanation for your findings.

Chapter 2 Skills Practice Lab 59

EARTH SCIENCE CONNECTION

A TOPOGRAPHIC MAP OF KEENE, NEW HAMPSHIRE

MAP SKILLS

Topographic maps use contour lines to indicate drain into the river around Site 3 or Site 2? Explain
areas that share a common elevation. Where the your answer.
lines are close together, the terrain is steep. Where
the lines are far apart, the landscape is flat. In 3. Identifying Trends Which site is more likely to be
this map, the Ashuelot River flows downhill from polluted? Explain your answer.
Site 1 to Site 3. Use the map to answer the ques-
tions below. 4. Analyzing Data Trace the sections of the Ashuelot
River between each site to determine the length of
1. Using a Key Use the scale at the top of the map stream between each site.
to calculate the distance between Sites 1 and 2 and
between Sites 2 and 3. 5. Interpreting Landforms A flood plain is an area
that is periodically flooded when a river overflows its
2. Understanding Topography Are the hills to the banks. Interpret the contour lines to locate the flood
east and west of the town of Keene more likely to plain of the Ashuelot River.

60 Chapter 2 Maps in Action

BATS AND BRIDGES In the 1990s, the Texas Depart- Congress Avenue Bridge in Austin
ment of Transportation and Bat to find out. Crevices under the
A large colony of Mexican free- Conservation International, a non- bridge appeared to be crucial, and
tailed bats lives under the Congress profit organization located in the crevices had to be the right size.
Avenue Bridge in Austin, Texas. Austin, set out to discover what Free-tailed bats appeared to prefer
These bats eat millions of insects a made a bridge attractive to bats. crevices 1 to 3 cm wide and about
night, so they are welcome neigh- They collected data on 600 30 cm deep in hidden corners of
bors. Communities around the coun- bridges, including some that had the bridge, and they preferred
try and around the world have bat colonies and some that did bridges made of concrete, not steel.
learned of the bats and have asked not. They answered the following
Austin for help in building bat- questions: Where was the bridge The scientists looked again at
friendly bridges. But all that the peo- located? What was it made of? their data on bridges. They dis-
ple of Austin knew was that the bats How was it constructed? Was it covered that 62 percent of bridges
appeared after the Congress Avenue over water or land? What was the in central and southern Texas that
Bridge was rebuilt in the 1980s. temperature under the bridge? had appropriate crevices were
What attracted the bats? The people How was the land around the occupied by bats. Now, the Texas
of Austin had to do a little research. bridge used? Department of Transportation is
adding bat houses to existing
A Crevice Will Do Some Bridges are Better bridges that do not have crevices.
These houses are known as Texas
In the wild, bats spend the day Statistical analysis of the data Bat-Abodes, and they can make
sleeping in groups in caves or in revealed a number of differences any bridge bat friendly.
crevices under the flaking bark of between bridges occupied by bats
old trees. They come back to the and bridges unoccupied by bats. Bat Conservation International
same place every day to roost. Which differences were important is collecting data on bats and bridges
Deep crevices in tree bark are rare to the bats and which were not? everywhere. Different bat species
now that many of our old forests The researchers returned to the may have different preferences. A
have been cut down, and many Texas Bat-Abode might not attract
bats are in danger of extinction. bats to a bridge in Minnesota or
Maine. If we can figure out what
features attract bats to bridges, we
can incorporate these features into
new bridges and make more
bridges into bat-friendly abodes.

What Do You Think?

Many bridges in the United
States could provide roosting
places for bats. Do you think
communities should try to
establish colonies of bats
under local bridges? How
should communities make
this decision, and what infor-
mation would they need to
make it wisely?

̈ Mexican free-tailed bats leave their roost under the Congress Avenue
Bridge in Austin, Texas, to hunt for insects.

Chapter 2 Society and the Environment 61

The Dynamic Earth 3C H A P T E R

1 The Geosphere

2 The Atmosphere

3 The Hydrosphere and

Biosphere

PRE-READING ACTIVITY

Pyramid
Before you
read this chap-
ter, create the
FoldNote entitled “Pyramid”
described in the Reading and
Study Skills section of the
Appendix. Label the sides of
the pyramid with
“Geosphere,” “Atmosphere,”
“Hydrosphere,” and
“Biosphere.” As you read the
chapter, write information
you learn about each cat-
egory under the
appropriate
flap.

Landmasses are moving slowly across
our planet’s surface. The atmosphere is
a swirling mix of gases and vapor. Our
planet, which may appear placid from
space, is always changing.

62 Chapter 3 The Dynamic Earth

SECTION 1

The Geosphere

EARTH SCIENCE CONNECTION

Molten rock from Earth’s interior flows over the surface of the Objectives
planet, and violent eruptions blow the tops off volcanoes.
Hurricanes batter beaches and change coastlines. Earthquakes ̈ Describe the composition and
shake the ground and topple buildings and freeway overpasses. structure of the Earth.
None of this activity is caused by people. Instead, it is the result
of the dynamic state of planet Earth. What are the conditions ̈ Describe the Earth’s tectonic
that allow us to survive on a constantly changing planet? plates.

The Earth as a System ̈ Explain the main cause of earth-
quakes and their effects.
The Earth consists of rock, air, water, and living things that all
interact with each other. Scientists divide this system into four ̈ Identify the relationship between
parts. As shown in Figure 1, the four parts are the geosphere volcanic eruptions and climate
(rock), the atmosphere (air), the hydrosphere (water), and the change.
biosphere (living things).
̈ Describe how wind and water
The solid part of the Earth that consists of all rock, as well as the alter the Earth’s surface.
soils and loose rocks on Earth’s surface, makes up the geosphere.
Most of the geosphere is located in Earth’s interior. At the equator, Key Terms
the average distance through the center of the Earth to the other
side is 12,756 km. The atmosphere is the mixture of gases that geosphere
makes up the air we breathe. Nearly all of these gases are found in crust
the first 30 km above the Earth’s surface. The hydrosphere makes mantle
up all of the water on or near the Earth’s surface. Much of this core
water is in the oceans. Water is also found in the atmosphere, on lithosphere
land, and in the soil. The biosphere is made up of parts of the geo- asthenosphere
sphere, the atmosphere, and the hydrosphere. The biosphere is the tectonic plate
part of the Earth where life exists. It is a thin layer at Earth’s sur- erosion
face that extends from about 9 km above the Earth’s surface down
to the bottom of the ocean. Figure 1 ̈ The Earth is an integrated
system that consists of the geosphere,
the atmosphere, the hydrosphere,
and the biosphere (inset).

Section 1 The Geosphere 63

www.scilinks.org Discovering Earth’s Interior

Topic: Composition of Studying the Earth beneath our feet is not easy. The deepest well that
the Earth has been drilled into Earth’s interior is only about 12 km deep. An
alternative method must be used to study the interior of the Earth.
Code: HE80329 Scientists can use seismic waves to learn about Earth’s interior.
Seismic waves are the waves that travel through Earth’s interior
Figure 2 ̈ Seismologists have meas- during an earthquake. If you have ever tapped a melon to see if it is
ured changes in the speed and direc- ripe, you know that the state of the melon’s interior affects the
tion of seismic waves that travel sound you detect. Similarly, a seismic wave is altered by the nature
through Earth’s interior. Through this of the material through which it travels. As shown in Figure 2, seis-
process, they have learned that the mologists measure changes in the speed and direction of seismic
Earth is made up of different layers. waves that penetrate the interior of the planet. By doing this, seis-
mologists have learned that the Earth is made up of different layers
and have inferred what substances make up each layer.

The Composition of the Earth Scientists divide Earth into three
layers—the crust, the mantle, and the core—based on their com-
position. These layers are composed of progressively denser mate-
rials toward the center of the Earth. Figure 3 shows a cross section
of the Earth. Earth’s thin outer layer, the crust, is composed
almost entirely of light elements. The crust makes up less than
1 percent of the Earth’s mass. The crust is the Earth’s thinnest
layer. It is 5 km to 8 km thick beneath the oceans and is 20 km to
70 km thick beneath the continents. The mantle, which is the

64 Chapter 3 The Dynamic Earth

layer beneath the crust, makes up 64 percent of the mass of the Figure 3 ̈ Earth’s Layers
Earth. The mantle is approximately 2,900 km thick and is made Scientists divide the Earth into
of rocks of medium density. Earth’s innermost layer is the core. different layers based on compo-
The core is composed of the densest elements. It has a radius of sition and physical properties.
approximately 3,400 km.

The Structure of the Earth If we consider the physical properties
of each layer, instead of their chemistry, the Earth can be divided
into five layers. Earth’s outer layer is the lithosphere. It is a cool,
rigid layer, 15 km to 300 km thick, that includes the crust and
uppermost part of the mantle. It is divided into huge pieces called
tectonic plates. The asthenosphere is the layer beneath the litho-
sphere. The asthenosphere is a plastic, solid layer of the mantle
made of rock that flows very slowly and allows tectonic plates to
move on top of it. Beneath the asthenosphere is the mesosphere, the
lower part of the mantle.

The Earth’s outer core is a dense liquid layer. At the center of
the Earth is the dense, solid inner core, which is made up mostly
of the metals iron and nickel. The temperature of the inner core
is estimated to be between 4,000ºC to 5,000ºC. It is solid because
it is under enormous pressure. Earth’s outer and inner core
together make up about one-third of Earth’s mass.

■✓● Reading Check Which of Earth’s physical layers is liquid? (See the

Appendix for answers to Reading Checks.)

Section 1 The Geosphere 65

North American Eurasian plate
plate

Pacific plate African Indian
plate plate

Nazca South American Australian
plate plate plate

Antarctic
plate

Figure 4 ̈ Earth’s lithosphere is Plate Tectonics
divided into pieces called tectonic
plates. The tectonic plates are mov- You learned that the lithosphere—the rigid, outermost layer of the
ing in different directions and at dif- Earth—is divided into pieces called tectonic plates. These plates
ferent speeds. glide across the underlying asthenosphere in much the same way
as a chunk of ice drifts across a pond. The continents are located
66 Chapter 3 The Dynamic Earth on tectonic plates and move around with them. The major tec-
tonic plates include the Pacific, North American, South American,
African, Eurasian, and Antarctic plates. Figure 4 illustrates the
major tectonic plates and their direction of motion.

Plate Boundaries Much of the geologic activity at the surface of
the Earth takes place at the boundaries between tectonic plates.
Plates may move away from one another, collide with one
another, or slip past one another. Enormous forces are generated
at tectonic plate boundaries, where the crust is pulled apart, is
squeezed together, or is constantly slipping. The forces produced
at the boundaries of tectonic plates can cause mountains to form,
earthquakes to shake the crust, and volcanoes to erupt.

Plate Tectonics and Mountain Building When tectonic plates
collide, slip by one another, or pull apart, enormous forces cause
rock to break and buckle. Where plates collide, the crust becomes
thicker, is pushed up, and eventually forms a mountain range. As
shown in Figure 5, the Himalaya Mountains in south-central Asia
began to form when the Eurasian tectonic plate and the Indian
tectonic plate began to push into each other about 50 million
years ago.

Earthquakes Figure 5 ̈ The Himalaya Mountains
are still growing today because the
A fault is a break in the Earth’s crust along which tectonic plate containing Asia and
blocks of the crust slide relative to one another. When the tectonic plate containing India
rocks that are under stress suddenly break along a fault, continue to collide.
a series of ground vibrations is set off. These vibrations
of the Earth’s crust caused by slippage along a fault are
known as earthquakes. Earthquakes are occurring all of
the time, but many are so small that we cannot feel
them. Other earthquakes are enormous movements of
the Earth’s crust that cause widespread damage.

The Richter scale is used by scientists to quantify
the amount of energy released by an earthquake. The
measure of the energy released by an earthquake is
called magnitude. The smallest magnitude that can be
felt is approximately 2.0, and the largest magnitude
that has ever been recorded is 9.5. Each increase of
magnitude by one whole number indicates the release
of 31.7 times more energy than the whole number
below it. For example, an earthquake of magnitude 6.0
releases 31.7 times the energy of an earthquake of
magnitude 5.0. Earthquakes that cause widespread
damage have magnitudes of 7.0 and greater.

Where Do Earthquakes Occur? Areas of the world where earth-
quakes occur are shown on the map in Figure 6. As you can see
from the map, the majority of earthquakes take place at or near
tectonic plate boundaries. Over the past 15 million to 20 million
years, large numbers of earthquakes have occurred along the San
Andreas fault, which runs almost the entire length of California.
The San Andreas fault is the line where parts of the North
American plate and the Pacific plate are slipping past one
another.

■✓● Reading Check What is meant by the magnitude of an earthquake?

Figure 6 ̈ The largest and most
active earthquake zones lie along
tectonic plate boundaries.

Section 1 The Geosphere 67

Connection to Biology Earthquake Hazard Despite much study, scientists cannot predict
when earthquakes will take place. However, information about
Can Animals Predict Earth- where they are most likely to occur can help people prepare for
quakes? Can animals that live them. An area’s earthquake-hazard level is determined by past
close to the site of an earthquake and present seismic activity. The Maps in Action activity located
detect changes in their physical at the end of this chapter shows earthquake-hazard levels for the
environment prior to an earth- contiguous United States.
quake? Documentation of
unusual animal behavior prior to Earthquakes are not restricted to high-risk areas. In 1886, an
earthquakes can be found as far earthquake shook Charleston, South Carolina, which is considered
back as 1784. Examples of this to be in a medium-risk area. Because the soil beneath the city is
odd behavior include zoo animals sandy, this earthquake caused extensive damage. During shaking
refusing to enter shelters at night, from a strong earthquake, sand acts like a liquid and causes build-
snakes and small mammals aban- ings to sink. In areas that are prone to earthquakes, it is worth the
doning their burrows, and wild extra investment to build bridges and buildings that are at least
birds leaving their usual habitats. partially earthquake resistant. Earthquake-resistant buildings are
These behaviors reportedly hap- slightly flexible so that they can sway with the ground motion.
pened within a few days, hours,
or minutes of earthquakes. Volcanoes

Figure 7 ̈ The Ring of Fire A volcano is a mountain built from magma—melted rock—that
Tectonic plate boundaries are places rises from the Earth’s interior to its surface. Volcanoes are often
where volcanoes usually form. The located near tectonic plate boundaries where plates are either col-
Ring of Fire contains nearly 75 percent liding or separating from one another. Volcanoes may occur on
of the world’s active volcanoes that land or under the sea, where they may eventually break the ocean
are on land. A large number of people surface as islands. As Figure 7 shows, the majority of the world’s
live on or near the Ring of Fire. active volcanoes on land are located along tectonic plate bound-
aries that surround the Pacific Ocean.

68 Chapter 3 The Dynamic Earth

Local Effects of Volcanic Eruptions A volcano erupts when the Figure 8 ̈ On May 18, 1980, Mount
pressure of the magma inside becomes so great that it blows open St. Helens in Washington State
the solid surface of the volcano. Some volcanoes have magma erupted. Sixty-three people lost their
flowing out of them all the time, so the pressure never builds up lives, and 400 km2 of forest were
and they never erupt. Volcanic eruptions can be devastating to destroyed in an eruption that blew
local economies and can cause great human loss. Clouds of hot away the top 410 m of the volcano.
ash, dust, and gases can flow down the slope of a volcano at
speeds of up to 200 km/h and sear everything in their path. During Comparison
an eruption, volcanic ash can mix with water and produce a mud- Table
flow. In addition, ash that falls to the ground can cause buildings Create the Graphic Organizer
to collapse under its weight, bury crops, and damage the engines of entitled “Comparison Table”
vehicles. Volcanic ash may also cause breathing difficulties. described in the Appendix. Label
the columns with “Local Effects”
Global Effects of Volcanic Eruptions Major volcanic eruptions, and “Global Effects.” Label the
such as the eruption of Mount St. Helens shown in Figure 8, can rows with “Volcanic Eruptions”
change Earth’s climate for several years. In large eruptions, clouds and “Earthquakes.” Then, fill in the
of volcanic ash and sulfur-rich gases may reach the upper atmo- table with details about the char-
sphere. As the ash and gases spread across the planet, they can acteristics and the
reduce the amount of sunlight that reaches the Earth’s surface. effects of each type
This reduction in sunlight can cause a drop in the average global of natural disaster.
surface temperature. In the 1991 eruption of Mount Pinatubo in
the Philippines, the amount of sunlight that reached the Earth’s Section 1 The Geosphere 69
surface was estimated to have decreased by 2 to 4 percent. As a
result, the average global temperature dropped by several tenths
of a degree Celsius over a period of several years.

Figure 9 ̈ Over long periods of Erosion
time, erosion can produce spectacular
landforms on Earth’s surface. Forces at the boundaries of tectonic plates bring rock to the surface
of the Earth. At the Earth’s surface, rocks are altered by other
forces. The Earth’s surface is continually battered by wind and
scoured by running water, which moves rocks around and changes
their appearance. The removal and transport of surface material is
called erosion. Erosion wears down rocks and makes them
smoother as time passes. The older a mountain range is, the longer
the forces of erosion have acted on it. This information helped
geologists learn that the round-topped Appalachian Mountains in

the eastern United States are older than
the jagged Rocky Mountains in the west.

Water Erosion Erosion by both rivers
and oceans can produce dramatic changes
on Earth’s surface. Waves from ocean
storms can erode coastlines to give rise to
a variety of spectacular landforms. Over
time, rivers can carve deep gorges into the
landscape, as shown in Figure 9.

Wind Erosion Like moving water, wind
can also change the landscape of our
planet. In places where plants grow, their
roots hold soil in place. But in places
where there are few plants, wind can
blow soil away very quickly. Beaches and
deserts, which have loose, sandy soil, are
examples of places where few plants
grow. Soft rocks, such as sandstone, erode
more easily than hard rocks, such as
granite, do. In parts of the world, spectac-
ular rock formations are sometimes seen
where pinnacles of hard rock stand alone
because the softer rock around them has
been eroded by wind and/or water.

S E C T I O N 1 Review

1. Name and describe the physical and compositional CRITICAL THINKING
layers into which scientists divide the Earth.
5. Analyzing Processes How might the surface of
2. Explain the main cause of earthquakes and their the Earth be different if it were not divided into tec-
effects. tonic plates?

3. Describe the effects that a large-scale volcanic erup- 6. Compare and Contrast Read about the effects of
tion can have on the global climate. erosion on mountains on this page. From what you
have read, describe the physical features you would
4. Describe how wind and water alter the Earth’s associate with a young mountain range and an old
surface. mountain range. READING SKILLS

70 Chapter 3 The Dynamic Earth

SECTION 2

The Atmosphere

EARTH SCIENCE CONNECTION

Earth is surrounded by a mixture of gases known as the Objectives
atmosphere. Nitrogen, oxygen, carbon dioxide, and other gases
are all parts of this mixture. Earth’s atmosphere changes con- ̈ Describe the composition of the
stantly as these gases are added and removed. For example, ani- Earth’s atmosphere.
mals remove oxygen from the atmosphere when they breathe in
and add carbon dioxide when they breathe out. Plants take in ̈ Describe the layers of the Earth’s
carbon dioxide and add oxygen to the atmosphere when they pro- atmosphere.
duce food. Gases can be added to and removed from the atmo-
sphere in ways other than through living organisms. A volcanic ̈ Explain three mechanisms of heat
eruption adds gases. A vehicle both adds and removes gases. transfer in Earth’s atmosphere.

The atmosphere also insulates Earth’s surface. This insulation ̈ Explain the greenhouse effect.
slows the rate at which the Earth’s surface loses heat. The
atmosphere keeps Earth at temperatures at which living things Key Terms
can survive.
atmosphere
Composition of the Atmosphere troposphere
stratosphere
Figure 10 shows the percentages of gases that make up Earth’s ozone
atmosphere. Nitrogen makes up 78 percent of the Earth’s atmo- radiation
sphere. It enters the atmosphere when volcanoes erupt and when conduction
dead plants and animals decay. Oxygen, the second most abun- convection
dant gas in Earth’s atmosphere, is primarily produced by plants. greenhouse effect
Other gases, including argon, carbon dioxide, methane, and
water vapor, make up the rest of the atmosphere. Nitrogen 78%

In addition to gases, the atmosphere contains many types of Oxygen
tiny, solid particles, or atmospheric dust. Atmospheric dust is 21%
mainly soil but includes salt, ash from fires, volcanic ash, particu-
late matter from combustion, skin, hair, bits of clothing, pollen,
bacteria and viruses, and tiny, liquid droplets called aerosols.

Other 1%

Figure 10 ̈ Nitrogen and oxygen
make up 99 percent of the composi-
tion of the atmosphere.

Figure 11 ̈ This sunrise scene that
was taken from space captures the
tropopause, the transitional zone that
separates the troposphere (yellow
layer) from the stratosphere (white
layer). The tropopause is the illumi-
nated brown layer.

Section 2 The Atmosphere 71

www.scilinks.org Air Pressure Earth’s atmosphere is pulled toward Earth’s surface
by gravity. As a result of the pull of gravity, the atmosphere is
Topic: Layers of the denser near Earth’s surface. Almost the entire mass of Earth’s
Atmosphere atmospheric gases is located within 30 km of our planet’s surface.
Fewer gas molecules are found at altitudes above 30 km; less pres-
Code: HE80861 sure at these altitudes pushes downward on atmospheric gases.
The air also becomes less dense as elevation increases, so breath-
Geofact ing at higher elevations is more difficult.

The Mesosphere In geology, the Layers of the Atmosphere
term mesosphere, which means
“middle sphere,” refers to the The atmosphere is divided into four layers based on temperature
2,550 km thick physical layer of the changes that occur at different distances above the Earth’s sur-
Earth that lies below the astheno- face. Figure 12 shows the four layers of Earth’s atmosphere.
sphere. The mesosphere is also the
name of the atmospheric layer that The Troposphere The atmospheric layer nearest Earth’s surface
extends from 50 to 80 km above is the troposphere. The troposphere extends to about 18 km
Earth's surface. above Earth’s surface. Almost all of the weather occurs in this
layer, as shown in Figure 13. The troposphere is Earth’s densest
atmospheric layer. Temperature decreases as altitude increases in
the troposphere.

0 2.0 i 104 Pressure (Pa) 1.0 i 105
6.0 i 104

600
500

Thermosphere
100

90

Altitude (km) 80 Temperature

70
Mesosphere

60

50

40 Ozone layer
30 Stratosphere
Figure 12 ̈ The layers of the atmo- 20 Pressure
sphere differ in temperature and
pressure. The red line indicates tem- 10
perature, and the green line indicates Troposphere
pressure in pascals.
0
72 Chapter 3 The Dynamic Earth –80 –70 –60 –50 –40 –30 –20 –10 0 10 20

Temperature (˚C)

The Stratosphere Above the troposphere is the stratosphere. The Figure 13 ̈ Scientists on board a
stratosphere extends from about 18 km to an altitude of about research plane from the National
50 km. Temperatures rise as altitude increases in the stratosphere. Oceanic and Atmospheric Admini-
This happens because ozone in the stratosphere absorbs the sun’s stration (NOAA) are making measure-
ultraviolet (UV) energy and warms the air. Ozone, O3, is a mole- ments of temperature, humidity,
cule made up of three oxygen atoms. Almost all the ozone in the barometric pressure, and wind speed
atmosphere is concentrated in the ozone layer in the stratosphere. as they fly over the eye of a hurricane.
Ozone reduces the amount of UV radiation that reaches Earth.
UV radiation can harm humans and other organisms. Figure 14 ̈ The aurora borealis, or
Northern Lights, can be seen in the
The Mesosphere The layer above the stratosphere is the meso- skies around Earth’s North Pole.
sphere. This layer extends to an altitude of about 80 km. The
mesosphere is the coldest layer of the atmosphere, and its temper- Section 2 The Atmosphere 73
atures have been measured as low as –93°C.

The Thermosphere The atmospheric layer farthest from Earth’s
surface is the thermosphere. In the thermosphere, nitrogen and
oxygen absorb solar radiation, which results in temperatures
above 2,000°C. Despite these high temperatures, the thermo-
sphere would not feel hot to us. Air particles that strike one
another transfer heat. The air in the thermosphere is so thin
that air particles rarely collide, so little heat is transferred.

Nitrogen and oxygen atoms in the lower region of the ther-
mosphere (about 80 km to 550 km above Earth’s surface) absorb
harmful solar radiation, such as X rays and gamma rays. This
absorption causes atoms to become electrically charged. Electri-
cally charged atoms are called ions. The lower thermosphere is
called the ionosphere. Sometimes ions radiate energy as light.
This light often glows in spectacular colors in the night skies near
the Earth’s North and South Poles, as shown in Figure 14.

■✓● Reading Check How does ozone in the stratosphere affect life on

the Earth’s surface?

QuickLAB Energy in the Atmosphere

The Heat As shown in Figure 15, energy from the sun is transferred in
Is On! Earth’s atmosphere by three mechanisms: radiation, convection,
and conduction. Radiation is the transfer of energy across space
Procedure and in the atmosphere. When you stand before a fire or a bed of
1. Fill two 250 mL beakers with coals, the heat you feel has reached you by radiation. Conduction
is the flow of heat from a warmer object to a colder object when
water. Use a thermometer to the objects are placed in direct physical contact. Convection is
record the initial temperature of the transfer of heat by air currents. Hot air rises and cold air
the water in both beakers. The sinks. Thus, if you hold your hand above a hot iron, you will feel
temperature of the water should the heat because a current of hot air rises up to your hand.
be the same for both beakers.
2. Wrap one beaker with white Heating of the Atmosphere Solar energy reaches the Earth as
paper, and wrap one with electromagnetic radiation, which includes visible light, infrared
black paper. Secure the paper radiation, and ultraviolet light. Our planet only receives about
with a piece of tape. two-billionths of this energy. But this seemingly small amount of
3. Place a 150 W floodlight 50 radiation contains a tremendous amount of energy. As shown in
cm away from the beakers, and Figure 15, about half of the solar energy that enters the atmo-
turn the light on. sphere passes through and reaches Earth’s surface. The rest is
4. Record the temperature of the absorbed or reflected in the atmosphere by clouds, gases, and
water in both beakers at 1 min, dust, or it is reflected by the Earth’s surface. On a sunny day,
5 min, and 10 min. rocks may become too hot to touch. If the Earth’s surface
Analysis continually absorbed energy, it would get hotter and hotter.
1. By what mechanism is energy
being transferred to the
beakers? Explain your answer.

Figure 15 ̈ Thermal Radiation
Three important mechanisms
responsible for transferring heat
in the atmosphere are radiation,

conduction, and convection.

74

This does not happen, because the oceans and the land radiate Ecofact
the energy they have absorbed back into the atmosphere.
Lost Weekend Have you ever
You may have noticed that dark-colored objects become much complained about how it always
hotter in the sun than light-colored objects. Dark-colored objects seems to rain on the weekends? If
absorb more solar radiation than light-colored objects, so dark- you live on the East Coast, you
colored objects have more energy to release as heat. This is one might actually have a point.
reason the temperature in cities is higher than the temperature in Researchers recently found that the
the surrounding countryside. mid-Atlantic states have a 30 to 40
percent greater chance of rain on
The Movement of Energy in the Atmosphere Air that is con- the weekends. Why? Researchers
stantly moving upward, downward, or sideways causes Earth’s suggest that the automobile
weather. In the troposphere, currents of less dense air, warmed by exhaust that accumulates in the
the Earth’s surface, rise into the atmosphere and currents of denser atmosphere over the course of the
cold air sink toward the ground. As a current of air rises into the work week has actually caused
atmosphere, it begins to cool. Eventually, the air current becomes weather patterns in this area to
more dense than the air around it and sinks instead of continuing shift. By Friday, the exhaust levels
to rise. So, the air current moves back toward Earth’s surface until are high enough to trigger rain
it is heated by the Earth and becomes less dense. Then, the air cur- over the weekend, which cleanses
rent begins to rise again. The continual process of warm air rising the atmosphere for another week.
and cool air sinking moves air in a circular motion, called a con-
vection current. A convection current is shown in Figure 15.

■✓● Reading Check Why does cool air sink and warm air rise in the

atmosphere?

Solar Energy that Reaches Earth

5% reflected by 20% absorbed by
the Earth’s surface ozone, clouds, and
atmospheric gases

50% absorbed by 25% scattered
the Earth’s surface and reflected by
clouds and air

Section 2 The Atmosphere 75

FIELD ACTIVITY The Greenhouse Effect

Exploring the Greenhouse The gases in Earth’s atmosphere act like the glass in the car
Effect Some of your classmates shown in Figure 16. Sunlight that penetrates Earth’s atmosphere
and teachers probably drive to heats the surface of the Earth. The Earth’s surface radiates heat
school. Given what you know back to the atmosphere, where some of the heat escapes into
about the reflection and absorp- space. The remainder of the heat is absorbed by greenhouse
tion of heat, go to the parking lot gases, which warms the air. Heat is then radiated back toward
on a sunny day and hypothesize the surface of the Earth. This process, in which gases trap heat
which cars will have the hottest near the Earth, is known as the greenhouse effect. Without the
interiors. Base your hypothesis on greenhouse effect, the Earth would be too cold for life to exist.
such variables as the color of car
interiors and whether the win- The gases in our atmosphere that trap and radiate heat are
dows are tinted or untinted. called greenhouse gases. None of the greenhouse gases have a
Record your observations in high concentration in Earth’s atmosphere. The most abundant
your Ecolog. greenhouse gases are water vapor, carbon dioxide, methane, and
nitrous oxide. The quantities of carbon dioxide and methane
Figure 16 ̈ The gases in the atmo- in the atmosphere vary considerably as a result of natural
sphere act like a layer of glass. Both and industrial processes, and the amount of water
glass and the gases in the atmosphere varies because of natural processes.
allow solar energy to pass through.
But glass and some of the gases in the
atmosphere absorb heat and stop the
heat from escaping into space.

S E C T I O N 2 Review CRITICAL THINKING

1. Describe the composition of Earth’s atmosphere. 5. Analyzing Processes Read about the density of
2. Describe a characteristic of each layer of the Earth’s atmosphere under the heading “Air Pressure.”
Write a paragraph that explains why Earth’s atmos-
atmosphere. phere becomes less dense with increasing altitude
3. Explain the three mechanisms of heat transfer in above Earth. WRITING SKILLS

Earth’s atmosphere. 6. Analyzing Processes How does human activity
4. Describe the role of greenhouse gases in Earth’s change some greenhouse-gas levels?

atmosphere.

76 Chapter 3 The Dynamic Earth

SECTION 3

The Hydrosphere and Biosphere

EARTH SCIENCE CONNECTION

Life on Earth is restricted to a very narrow layer around the Objectives
Earth's surface. In this layer, called the biosphere, everything that
organisms need to survive can be found. One of the requirements ̈ Name the three major processes in
of living things is liquid water. the water cycle.

The Hydrosphere and Water Cycle ̈ Describe the properties of ocean
water.
The hydrosphere includes all of the water on or near the Earth's
surface. The hydrosphere includes water in the oceans, lakes, ̈ Describe the two types of ocean
rivers, wetlands, polar icecaps, soil, rock layers beneath Earth's currents.
surface, and clouds.
̈ Explain how the ocean regulates
The continuous movement of water into the air, onto land, Earth’s temperature.
and then back to water sources is known as the water cycle,
which is shown in Figure 17. Evaporation is the process by which ̈ Discuss the factors that confine life
liquid water is heated by the sun and then rises into the atmo- to the biosphere.
sphere as water vapor. Water continually evaporates from Earth's
oceans, lakes, streams, and soil, but the majority of the water evap- ̈ Explain the difference between
orates from the oceans. In the process of condensation, water open and closed systems.
vapor forms water droplets on dust particles. These water
droplets form clouds, in which the droplets collide, stick together, Key Terms
and create larger, heavier droplets. These larger droplets fall from
clouds as rain in a process called precipitation. Precipitation may water cycle
also take the form of snow, sleet, or hail. evaporation
condensation
precipitation
salinity
fresh water
biosphere

Figure 17 ̈ The major processes
of the water cycle include

evaporation, condensation,
and precipitation.

Section 3 The Hydrosphere and Biosphere 77

Connection to Geology Earth’s Oceans

Submarine Volcanoes Geolo- We talk about the Atlantic Ocean, the Pacific Ocean, the Arctic
gists estimate that approximately Ocean, and the Indian Ocean. However, if you look at Figure 18,
80 percent of the volcanic activity you see that these oceans are all joined. This single, large, inter-
on Earth takes place on the ocean connected body of water is called the world ocean. Its waters
floor. Most of this activity occurs cover a little over 70 percent of the Earth’s surface. As we will
as magma slowly flows onto the see, the world ocean plays many important roles in regulating our
ocean floor where tectonic plates planet’s environment.
pull away from each other. But
enormous undersea volcanoes are The largest ocean on Earth is the Pacific Ocean. It covers a sur-
also common. Off the coast of face area of approximately 165,640,000 km2 and has an average
Hawaii, a submarine volcano depth of 4,280 m. The deepest point on the ocean floor is in the
called the Loihi Seamount rises Pacific Ocean. This point is called the Challenger Deep and is
5,185 m from the ocean floor. located east of the Philippine Islands at the bottom of the Mariana
Loihi is just 915 m below the Trench. The Challenger Deep is 11,033 m below sea level, which is
ocean’s surface, and in several deeper than Mount Everest is tall. Oceanographers often divide the
thousand years, this volcano may Pacific Ocean into the North Pacific and South Pacific based on the
become the next Hawaiian Island. direction of surface current flow in each half of the Pacific Ocean.
Surface currents in the Pacific move in a clockwise direction north

Hydrothermal Vents

The light from your tiny research dive, many more hydrothermal ̈ Superheated, mineral-rich water
submarine illuminates the desert- vents have been located on the streams through a chimney at a
like barrenness of the deep-ocean ocean bottom. hydrothermal vent on the floor of
floor. Suddenly, the light catches the Pacific Ocean.
something totally unexpected—an Hydrothermal vents are
underwater oasis teeming with sea openings in the ocean floor water cools from above 100°C to
creatures that no human has laid where super-hot, mineral-rich less than 50°C. The tallest chimney
eyes on before. At the center of waters stream into the ocean. reported to date is 49 m. Vent
this community is a tall chimney- Hydrothermal vents form
like structure from which a column where tectonic plates are sepa-
of black water is rising. rating and where deep frac-
tures are opening in the Earth’s
This scene is much like the one crust. Water seeps down into
that John Corliss and John Edmond some of these fractures to a
witnessed when they discovered the depth where it is heated by molten
first deep-sea hydrothermal vents rock and enriched with minerals.
and the odd community of creatures The water returns to the ocean floor
that inhabit them. Corliss’s and through other fractures and then
Edmond’s discovery was made dur- pours into the ocean. Water often
ing a dive in the submarine Alvin in streams through structures called
early 1977. The dive site was in the chimneys. Chimneys form when the
eastern Pacific Ocean near the minerals in the vent water—mostly
Galápagos Islands. Since the original iron and sulfur—precipitate as the

78 Chapter 3 The Dynamic Earth