1. Science differs from other fields of study in that its goal is to understand and explain natural events using observations and experiments, rather than answer philosophical questions. Scientists assume nature is understandable and predictable. 2. Scientific methods involve making observations and measurements, asking questions, developing hypotheses, experimentation and testing, analyzing results, and communicating findings. Hypotheses must be tested and evidence evaluated through peer review before new scientific theories are accepted. 3. Scientific knowledge advances through an ongoing process as new discoveries are shared, reviewed, built upon, and integrated across disciplines over time, potentially leading hypotheses to become accepted theories or revealing flaws requiring revision. This benefits society by furthering understanding and enabling new technologies.

1. Name Class Date
CHAPTER 1 Introduction to Earth Science
SECTION
2 Science as a Process
KEY IDEAS
As you read this section, keep these questions in mind:
• How is science different from other fields of study?
• What are scientific methods?
• How does scientific knowledge change?
• How does science affect society?
How Is Science Different from Other Fields
of Study?
Art, architecture, philosophy, and science are all READING TOOLBOX
examples of fields of study. However, science has dif-
Organize As you read, make
ferent goals than other fields of study. For example, an outline of this section.
a philosopher may ask questions such as “Why do we Use the headings from the
exist?” or “What is the place of humans in the universe?” section in your outline.
Scientists do not seek to answer questions such as these.
Instead, the goal of scientists is to explain natural events.
Scientists look for answers about how the natural
world works by making observations and by doing
experiments. As they study the natural world, scientists
assume two things:
• It is possible to understand nature.
• Nature is predictable. READING CHECK
Scientists must first assume that people can under- 1. Explain What are two
stand nature. That is, scientists assume that with the right assumptions that all
scientists make?
tools and correct methods, they can find the answers
they are looking for. There are many natural events that
scientists do not yet understand. Scientists assume that
they will someday be able to understand these events.
Scientists also assume that nature is predictable. In
general, scientists observe patterns in nature. From the
way a pattern repeats, scientists can predict that an event
will happen in a similar way in the future. For example,
suppose a scientist observes that certain weather condi-
tions happen before a tornado forms. The scientist may
predict that when these same weather conditions happen
again, another tornado will form.
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Holt McDougal Earth Science 5 Introduction to Earth Science

2. Name Class Date
SECTION 2 Science as a Process continued
What Are Scientific Methods?
Over time, scientists have developed methods, or a set
of ways, to study the natural world. The methods scien-
tists use are organized and logical. However, these
scientific methods are not a set of rules that scientists
must follow in an exact order. Instead, scientific methods
are guidelines that scientists follow to help them solve
LOOKING CLOSER scientific problems. The flowchart below shows one way
2. Infer Why is there an
arrow pointing from
that a scientist may use scientific methods.
“Drawing conclusions” to
“Asking questions”? Making Asking Forming a
observations questions hypothesis
Testing a Drawing Comunicating
hypothesis conclusions results
OBSERVING AND ASKING QUESTIONS
Scientific methods generally begin with observation.
Observation is the process of using the five senses to
collect information about the world. When you compare
the colors and texture of two different rocks or listen to
waves crashing on a beach, you are making observations.
Observations that scientists make often lead them to
ask questions. For example, a scientist might observe
that the weather is often cooler after a thunderstorm. He
may then ask the question, “Why is the weather cooler
after a thunderstorm?”
FORMING A HYPOTHESIS
Once scientists have asked a question and made a
READING CHECK few observations, they might then form a hypothesis. A
3. Explain On what do hypothesis is a possible way to explain or solve a prob-
scientists base their lem. Scientists base their hypotheses on observations or
hypotheses? on known facts about similar events.
For example, a scientist might know that when hot
air and cool air mix, they can form clouds and rain. She
could make the hypothesis that thunderstorms happen
when cool air moves into an area and mixes with hot air.
The mixing air causes the thunderstorm. The weather is
cooler after the storm because the cool air has moved
into the area.
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Holt McDougal Earth Science 6 Introduction to Earth Science

3. Name Class Date
SECTION 2 Science as a Process continued
TESTING THE HYPOTHESIS
After scientists form a hypothesis, they look for ways
to test it in an investigation. In some investigations, the
scientist will make more observations and see if they fit
the hypothesis. For example, a scientist may use tools
to study the movements of cool and warm air. He could
use the measurements he takes to learn whether cool air
moves into an area after a thunderstorm.
In other investigations, a scientist will do an experi-
ment to test a hypothesis. An experiment is a set of pro-
cedures that a scientist carries out. Every experiment
has conditions or factors that can change. These factors
are called variables. There are two types of variables.
Independent variables are factors that the scientist
changes. Dependent variables are factors that change
as a result of the independent variables. READING CHECK
For example, suppose a scientist did an experiment to 4. Discuss What are two
learn how water affects a plant’s growth. The indepen- ways scientists can test a
hypothesis?
dent variable is the amount of water the plants get. The
dependent variable is how much the plants grow. In this
experiment, the scientist would change only the amount
of water each plant gets. She would keep all other condi-
tions, such as amount of sunlight, temperature, and type
of plant, the same.
This astronaut, Shannon
Lucid, is observing wheat LOOKING CLOSER
plants growing in space. 5. Apply Ideas What might
Experiments like this one be the dependent variable in
will help scientists learn Shannon Lucid’s experiment?
how plants grow in space
where the pull of Earth’s
gravity is weaker.
DRAWING CONCLUSIONS
Scientists must decide if their observations support
the hypothesis, or show that the hypothesis was correct.
In many cases, the results of an experiment are unex-
pected. If the results do not support the hypothesis, the
scientists must throw out the hypothesis or change it.
Unexpected results are important to science. They can
cause scientists to ask new questions.
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Holt McDougal Earth Science 7 Introduction to Earth Science

4. Name Class Date
SECTION 2 Science as a Process continued
How Do Scientists Use Models?
In Earth science, it is often impossible to use an exper-
iment to test a hypothesis. Instead, scientists make addi-
tional observations to gather evidence. Then they test the
hypothesis by thinking about how well the hypothesis
explains the evidence that they gathered.
Scientists also may use models to test hypotheses they
cannot test using an experiment. A model is a description
or a representation of an object, an idea, a system, or
an event. Some models describe objects, such as atoms.
Others describe processes, such as the water cycle.
Scientists often use models to study things that are too
big, too small, too fast, too slow, or too dangerous to
READING CHECK study directly.
6. Explain What is the main
reason scientists use models? TYPES OF MODELS
The table below describes five types of models that
scientists use.
Type of Model Definition Examples
Physical three-dimensional models globe
Graphical two-dimensional models map, chart
(pictures)
Conceptual description of an idea flowchart
Mathematical mathematical equation that 2 ϩ 2 ϭ 4 (used to represent
describes the way a system two items joined to two
or process works other items)
Computer a type of mathematical computer model of Mount
model that uses a Everest
computer to do calculations
and display results
LOOKING CLOSER
7. Evaluate Methods What
are two advantages this
physical model has over the This scientist is working
actual mountain? with a physical model of
Mount Everest. The model
has the same shape and
relative position of the
features that the real
mountain has.
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Holt McDougal Earth Science 8 Introduction to Earth Science

5. Name Class Date
SECTION 2 Science as a Process continued
How Do Scientists Make Accurate
Measurements?
Scientists gather information during investigations.
Measurement is a very important method for gathering
information in most scientific investigations.
SI UNITS
Scientists need to be able to compare and analyze each
other’s results. Therefore, scientists around the world use
a common system of measurement. The system is called
the International System of Units, or SI. Meters and
kilograms are examples of SI units. READING CHECK
8. Explain Why is the
ACCURACY AND PRECISION International System of Units
important?
Accuracy and precision are two ways to describe mea-
surements. Accuracy describes how close a measurement
is to the true value. Precision describes how exact a mea-
surement is. For example, stating the length of a string
as 1 m is less precise than stating that the length of the
string is 1.05 m.
A measurement can be accurate but not precise.
A measurement can also be precise but not accurate.
Scientists want to have measurements that are both accu-
rate and precise. The figure below shows the difference
between accuracy and precision.
LOOKING CLOSER
9. Infer If there were
Good overall accuracy but poor precision Poor accuracy but good precision another picture labeled “Poor
accuracy and poor precision,”
what would it look like?
Good accuracy and good precision
No measurement can be completely precise. There are
two ways to express error: as a percentage error or as a
confidence interval.
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Holt McDougal Earth Science 9 Introduction to Earth Science

6. Name Class Date
SECTION 2 Science as a Process continued
PERCENTAGE ERROR
Math Skills A percentage error is one way of expressing how far
10. Calculate You have a measured value is from the true value. You can use
made a meterstick out of the following equation to find the percentage error of
cardboard, but you’re not
sure how accurate it is. You a measurement.
measure your stick against a
real meterstick. You find that
your meterstick is only 90 cm
percentage error ϭ [(actual value − measured value)] × 100
actual value
long. What is your percentage
error? CONFIDENCE INTERVAL
A confidence interval describes the range of values
for a sample of measurements. For example, suppose
a scientist wants to express the values for the length of
ears of corn in a field. The average length of all the ears
of corn in the field is 23 cm. Of all the ears, 90% of them
Talk About It are within 3 cm of this average length. The scientist may
Calculate As a class, make report the average length of all the ears of corn in the
a list of shoe sizes. Discuss field as “23 Ϯ 3 cm with 90% confidence.”
what confidence interval you
could use to discuss shoe
sizes. How Does Scientific Knowledge Grow?
When scientists discover something new, they share
their ideas with other scientists. The other scientists
review and test the ideas before accepting the new ideas.
SHARING RESULTS
Scientists typically share their results as papers in sci-
entific journals. They also share ideas at meetings with
other scientists. Many journals are now published online
so that scientists can share their ideas more quickly and
easily.
PEER REVIEW
Before scientists publish their work, they show it to
other scientists who are experts on the topic. Those
READING CHECK experts review the work. The reviewers may suggest
changes to the investigation. They may also point out
11. Define What happens
during peer review?
errors in thinking that scientists did not see. This process
is called peer review.
If reviewers think that the ideas are incorrect or that
the investigation was invalid, or flawed, the journal will
not publish the paper. The peer review process helps
make sure only well-supported ideas are published.
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Holt McDougal Earth Science 10 Introduction to Earth Science

7. Name Class Date
SECTION 2 Science as a Process continued
DEVELOPING A THEORY
After a scientist publishes his ideas and results, other
scientists typically test the hypothesis and build on the
results. The process of repeated testing may continue for
years. In time, the hypothesis may be proved incorrect,
be changed, or be accepted by most scientists.
When a hypothesis has been tested many times and
becomes accepted, the hypothesis may help form a
theory. A theory is an explanation that is supported by
all existing observations and study results. However, if
repeated results from later tests do not support the
theory, scientists may need to change it. READING CHECK
12. Identify Relationships
THE IMPORTANCE OF INTERDISCIPLINARY SCIENCE What is the relationship
Scientists from many different fields of science share between a hypothesis and a
theory?
their ideas. Sharing ideas between fields is important
because discoveries in different fields may add support
to one idea. When an idea is supported by evidence
from more than one field, the idea is more likely to be
accurate.
The figure below shows one hypothesis that is based
on evidence from several fields of science.
Paleontology Geology Astronomy Climatology
(study of fossils)
Scientists found All over Earth, Scientists have
No dinosaur a large impact iridium appears in used computer
fossils exist in crater in the ocean rocks that are models to show
LOOKING CLOSER
rock layers that that is about 65 about 65 million what would
are less than 65 million years old. years old. Iridium happen if a large
million years old. is rare on Earth, asteroid hit Earth.
but is common in They have found 13. Draw Conclusions
asteroids. that it would
Impact Hypothesis change Earth’s Suppose scientists find
of Extinction of the climate and affect
Dinosaurs life on Earth.
evidence of dinosaur fossils
that are only 30 million years
Discoveries and ideas from different fields of science have helped scientists old. What effect would this
develop a hypothesis about how dinosaurs became extinct. new evidence have on the
hypothesis that the figure
describes?
Scientific knowledge helps people understand the
natural world. It also helps people develop new technolo-
gies, such as tools, materials, and processes.
Many technologies are helpful, but some new technol-
ogies can cause problems. For example, plastic is a tech-
nology that is useful in many products. However, plastics
can cause pollution and harm wildlife. An understanding
of science is important for all citizens. Thinking scientifi-
cally can help people make wise decisions about prod-
ucts they buy, where they live, and even how they vote.
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Holt McDougal Earth Science 11 Introduction to Earth Science

8. Name Class Date
Section 2 Review
SECTION VOCABULARY
dependent variable in an experiment, the observation the process of obtaining informa-
factor that changes as a result of manipulation tion by using the senses; the information
of one or more other factors (the independent obtained by using the senses
variables) peer review the process in which experts in
hypothesis a testable idea or explanation that a given field examine the results and conclu-
leads to scientific investigation sions of a scientist’s study before that study is
independent variable in an experiment, the accepted for publication
factor that is deliberately manipulated theory a system of ideas that explains many
related observations and is supported by a
large body of evidence acquired through
scientific investigation
1. Identify Relationships What is the relationship between a dependent variable and
an independent variable?
2. List What are the six main processes that are part of scientific methods?
3. Compare What is the difference between accuracy and precision?
4. Explain Why is peer review of a scientific paper important?
5. Apply Ideas Give one example of a technology that can be both helpful and
harmful. Think of a different example from the one given in the text.
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Holt McDougal Earth Science 12 Introduction to Earth Science