## National Geographic

Figure 1.6 Scientific methods are used by scientists to help organize and plan their experiments and investigations. The flow chart below outlines some of the methods commonly used by scientists.

Observe an unexplained phenomenon.

Collect information. Make observations.

Ask questions. Use prior knowledge. Review related research.

Form a hypothesis.

Design an experiment to test the chosen hypothesis.

Conduct an experiment and record the data

 Actual results Compare Expected results

Repeat experiment many times until results are consistent.

Refine and test an alternate hypothesis.

Draw a conclusion.

Hypothesis is supported.

Draw a conclusion.

Hypothesis is not supported.

Report results of the experiment.

Compare results from similar experiments.

Accepted hypothesis

Additional experimentation based on accepted hypothesis m ^n£1'ltI Jn To explore more about scientific methods, visit glencoe.com. 1 Earth ¡¿r. Scienc^ Section 2 • Methods of Scientists 11

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Report results of the experiment.

Determine the Relationship Between Variables

How do the rates of heat absorption and release vary between soil and water?

Different substances absorb and release heat at different rates.

Procedure ^ El t^

1. Read and complete the lab safety form.

2. Read the procedure and create a data table to record your temperature results.

3. Pour soil into one container until it is half full. Pour water into a second container until it is half full. Leave a third container empty.

4. Place one thermometer in the soil so that the bulb is barely covered. Use masking tape to secure another thermometer about 1 cm from the top of the soil.

5. Repeat Step 4 for the empty container and the container with water.

6. Put the containers on a sunny windowsill. Record the temperature shown on each thermometer. Write these values in a table. Record temperature readings every 5 min for 30 min.

7. Remove the containers from the windowsill and continue to record the temperature on each thermometer every 5 min for 30 min.

Analysis

1. Determine Which substance absorbed heat more quickly? Which substance lost heat more quickly?

2. Specify What was your independent variable? What was your dependent variable?

Experimentation An experiment is classified as an organized procedure that involves making observations and measurements to test a hypothesis. Collecting good qualitative and quantitative data is vital to the success of an experiment.

Imagine a scientist is conducting an experiment on the effects of acid on the weathering of rocks. In this experiment, there are three different samples of identical rock pieces. The scientist does not add anything to the first sample. To the second and third samples, the scientist adds two different strengths of acid. The scientist then makes observations (qualitative data) and records measurements (quantitative data) based on the results of the experiment.

A scientific experiment usually tests only one changeable factor, called a variable, at a time. The independent variable in an experiment is the factor that is changed by the experimenter. In the experiment described above, the independent variable was the strength of the acid.

A dependent variable is a factor that is affected by changes in the independent variable. In the experiment described above, the dependent variable was the effect of the acid on the rock samples.

Constants are factors that do not change during an experiment. Keeping certain variables constant is important to an experiment. Placing the same amount of acid on each rock tested, or using the same procedure for measurement, are two examples. A control is used in an experiment to show that the results of an experiment are a result of the condition being tested. The control for the experiment described above was the rock that did not have anything added to it. You will experiment with variables in the MiniLab on this page and in many other activities throughout this textbook.

^P Reading Check Explain the difference between a dependent and an independent variable.

Investigation Earth scientists cannot always control the aspects of an experiment. It would be impossible to control the rainfall or temperature when studying the effects of a new fertilizer on thousands of acres of corn. When this is the case, scientists refer to their research as an investigation. An investigation involves observation and collecting data but does not include a control. Investigations can often lead scientists to design future experiments based on the observations they have made.

Safety Many of the experiments and investigations in this book will require that you handle various materials and equipment. When conducting any scientific investigation, it is important to use all materials and equipment only as instructed. Refer to the Reference Handbook for additional safety information and a table of safety symbols.

Analysis and conclusions New ideas in science are carefully examined by the scientist who made the initial discovery and by other scientists in the same field. Processes, data, and conclusions must be examined to eliminate influence by expectations or beliefs, which is called bias. During a scientific experiment, all data are care fully recorded. Once an experiment is complete, graphs, tables, and charts are commonly used to display data. These data are then analyzed so that a conclusion can be drawn. Many times, a conclusion does not support the original hypothesis. In such a case, the hypoth esis must be reevaluated and further research must be conducted.

### Measurement

Scientific investigations often involve making measurements. A measurement includes both a number and a unit of measure. Scientific investigations use a standard system of units called Le Système International d'Unités (SI), which is a modern version of the metric system. SI is based on a decimal system that uses the number 10 as the base unit. See Table 1.2 for information on SI and metric units of measure commonly used in science.

Length The standard SI unit to measure length is the meter (m). The distance from a doorknob to the floor is about 1 m. The meter is divided into 100 equal parts called centimeters (cm). Thus, 1 cm is 1/100 of 1 m. One millimeter (mm) is smaller than 1 cm. There are 10 mm in 1 cm. Longer distances are measured in kilometers (km). There are 1000 m in 1 km.

Vocabulary

Bias to influence in a particular, typically unfair, direction; prejudice Their choice of teammates showed a bias toward their friends

 Table 1.2 Measurement and Units 1 Measurement SI and Metric Units Commonly Used in Science Length millimeter (mm), centimeter (cm), meter (m), kilometer (km) Mass and weight gram (g), kilogram (kg), metric ton Area square meter (m2), square centimeter (cm2)* Volume cubic meter (m3)*, milliliter (mL), liter (L) # Density grams per cubic centimeter (g/cm3), grams per milliliter (g/mL), kilograms per cubic meter (kg/m3) Time second (s), hour (h) Temperature kelvin (K) * units derived from SI units # commonly used metric units

Mass The amount of matter in an object is called mass. Mass depends on the number and types of atoms that make up the object. The mass of an object is the same no matter where the object is located in the universe. The SI unit of mass is the kilogram (kg).

Weight Weight is a measure of the gravitational force on an object. Weight is typically measured with some type of scale. Unlike mass, weight varies with location. For example, the weight of an astronaut while on the Moon is about one-sixth the astronaut's weight on Earth. This is because the gravitational force exerted by the Moon on the astronaut is one-sixth the force exerted by Earth on the astronaut. Weight is a force, and the SI unit for force is the newton (N). A 2-L bottle of soft drink with a mass of 2 kg weighs about 20 N on Earth.

^p Reading Check Compare mass and weight.

Area and volume Some measurements, such as area, require a combination of SI units. Area is the amount of surface included within a set of boundaries and is expressed in square units of length, such as square meters (m2).

The amount of space occupied by an object is the object's volume. The SI units for volume, like those for area, are derived from the SI units used to measure length. The basic SI unit of volume for a solid object is the cubic meter (m3). Measurements for fluid volumes are usually made in milliliters (mL) or liters (L). Liters and milliliters are metric units that are commonly used to measure liquid volumes. Volume can also be expressed in cubic centimeters (cm3)—1 cm3 equals 1 mL.

Figure 1.7

Major Events in Earth Science

Many discoveries during the twentieth and early twenty-first centuries revolutionized our understanding of Earth and its systems.

Figure 1.7

Major Events in Earth Science

Many discoveries during the twentieth and early twenty-first centuries revolutionized our understanding of Earth and its systems.

1913 French physicists discover the ozone layer in Earth's upper atmosphere and propose that it protects Earth from the Sun's ultraviolet radiation.

15 uo

1907 Scientists begin using radioactive decay to determine that Earth is billions of years old. This method will be used to develop the first accurate geological time scale.

1913 French physicists discover the ozone layer in Earth's upper atmosphere and propose that it protects Earth from the Sun's ultraviolet radiation.

1907 Scientists begin using radioactive decay to determine that Earth is billions of years old. This method will be used to develop the first accurate geological time scale. 1925 Cecilia Payne's analysis of the spectra of stars reveals that hydrogen and helium are the most abundant elements in the universe. 1955 Louis Essen invents a highly accurate atomic clock that tracks radiation emitted and absorbed by cesium atoms.

1M4IJ

1925 Cecilia Payne's analysis of the spectra of stars reveals that hydrogen and helium are the most abundant elements in the

universe.

1936 Inge Lehmann discovers the inner core of Earth 5121 km below the planet's surface by studying seismic waves.

14 Chapter 1 • The Nature of Science

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Density The measure of the amount of matter that occupies a given space is density. Density is calculated by dividing the mass of the matter by its volume. Density is often expressed in grams per cubic centimeter (g/cm3), grams per milliliter (g/mL), or kilograms per cubic meter (kg/m3).

Time The interval between two events is time. The SI unit of time is the second. In the activities in this book, you will generally measure time in seconds or minutes. Time is usually measured with a watch or clock. The atomic clock provides the most precise measure of time currently known. Known as UTC, Coordinated Universal Time is based on the atomic clock element cesium-133 and is adapted to the astronomical demarcation of day and night. See Figure 1.7 for more information on the invention of the atomic clock and other advances in Earth science.

Temperature A measure of the average kinetic energy of the particles that make up a material is called temperature. A mass made up of particles that vibrate quickly generally has a higher temperature than a mass whose particles vibrate more slowly. Temperature is measured in degrees with a thermometer. Scientists often measure temperature using the Celsius (°C) scale. On the Celsius scale, a comfortable room temperature is about 21°C, and the normal temperature of the human body is about 37°C.

The SI unit for temperature is the kelvin (K). The coldest possible temperature, absolute zero, was established as 0 K or -273 °C. Since both temperature units are the same size, the difference between the two scales (273) is used to convert from one scale to another. For example, the temperature of the human body is 37°C, to which you would add 273 to get 310 K.

Vocabulary

Interval space of time between two events or states

### The interval for pendulum swings was three seconds

1962 Harry Hess's seafloor spreading hypothesis, along with the discoveries made about the ocean floor, lays the foundation for plate tectonic theory.

libSO

1979-1980 Magsat, a NASA satellite, takes the first global measurement of Earth's magnetic field.

1970 George Carruthers' ultraviolet camera and spec-trograph, placed on the Moon's surface, analyzes pollutants in Earth's atmosphere and detects interstellar hydrogen.

1970 George Carruthers' ultraviolet camera and spec-trograph, placed on the Moon's surface, analyzes pollutants in Earth's atmosphere and detects interstellar hydrogen. 1990 The Hubble Space Telescope goes into orbit, exploring Earth's solar system, measuring the expansion of the universe, and providing evidence of black holes.

? 2004 A sediment core retrieved from the ocean floor discloses 55 million years of Earth's atmospheric and climatic history. The sample reveals that the north pole once had a warm climate.

1990 The Hubble Space Telescope goes into orbit, exploring Earth's solar system, measuring the expansion of the universe, and providing evidence of black holes.

Section 2 • Methods of Scientists 15

NASA/epa/Corbis Figure 1.8 On a 5-km-long beach, such as the one shown above, there might be 8 x 1015 grains of sand. The average size of a grain of sand is 0.5 mm.

Scientific Notation

In many branches of science, some numbers are very small, while others are very large. To express these numbers conveniently, scientists use a type of shorthand called scientific notation, in which a number is expressed as a value between 1 and 10 multiplied by a power of 10. The power of 10 is the number of places the decimal point must be shifted so that only a single digit remains to the left of the decimal point.

If the decimal point must be shifted to the left, the exponent of 10 is positive. Figure 1.8 shows a beach covered in sand. The number of grains of sand on Earth has been estimated to be approximately 4,000,000,000,000,000,000,000. In scientific notation, this number is written as 4 X 1021.

In astronomy, masses and distances are usually so large that writing out the numbers would be cumbersome. For example, the mass of Earth at 5,974,200,000,000,000,000,000,000 kg would be written as 5.9742 X 1024 kg in scientific notation.

If the decimal point in a number must be shifted to the right, the exponent of 10 is negative. The diameter of an atom in meters, for example, which is approximately 0.0000000001 m, is written as 1 X 10-10 m.

Section 1.2 Assessment

Section Summary

### I Scientists work in many ways to gather data.

I A good scientific experiment includes an independent variable, dependent variable, and control. An investigation, however, does not include a control.

I Graphs, tables, and charts are three common ways to communicate data from an experiment.

I SI, a modern version of the metric system, is a standard form of measurement that all scientists can use.

I To express very large or very small numbers, scientists use scientific notation.

Understand Main Ideas

1. imanExplain why scientific methods are important and why there is not one established way to conduct an investigation.

2. Compare and contrast the purpose of a control, an independent variable, and a dependent variable in an experiment.

3. Calculate Express 0.00049386 in scientific notation.

4. Calculate Convert the temperature 49°C to kelvin.

5. Compare and contrast volume and density.

### Think Critically

6. Construct a plan to test the absorption of three different kinds of paper towels, including a control, dependent variable, and independent variable.

7. Explain which is more useful when comparing mass and weight on different planets.

OBX» Earth Science

8. If you have 20 mL of water, how many cubic centimeters of water do you have?

16 Chapter 1 • The Nature of Science

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Science

Self-Check Quiz glencoe.com

16 Chapter 1 • The Nature of Science

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Science

Section 1.3

### Objectives

I Explain why precise communication is crucial in science. I Compare and contrast scientific theories and scientific laws. I Identify when it is appropriate to use a graph or a model.

Review Vocabulary hypothesis: testable explanation of a situation

New Vocabulary scientific model scientific theory scientific law Communication in Science

MANŒSS Precise communication is crucial for scientists to share their results effectively with each other and with society.

Real-World Reading Link If you read an advertisement for a product called "Glag" without any description, would you know whether to eat it or wear it? When a scientist does an investigation, he or she has to describe every part of it precisely so that everyone can understand his or her conclusions.

### Communicating Results

There are many ways to communicate information, such as newspapers, magazines, TV, the Internet, and scientific journals. Think back to the Launch Lab from the beginning of the chapter. Although you and your lab partner both used the same form of communication, were your descriptions identical? Scientists have the responsibility to truthfully and accurately report their methods and results. To keep them ethical, a system of peer review is used in which scientists in the same field verify each other's results and examine procedures and conclusions for bias. Communicating scientific data and results, as the scientists are shown doing in Figure 1.9, also allows others to learn of new discoveries and conduct new investigations that build on previous investigations.

Lab reports Throughout this book, you will conduct many Earth science investigations and experiments. During and after each, you will be asked to record and analyze the information that you collected and to draw conclusions based on your data. Your written account of each lab is your lab report. This will be used by your teacher to assess your understanding. You might also be asked to compare your results with those of other students to help you find both similarities and differences among the results.

Figure 1.9 Scientists, like those shown in the photo, communicate data and discoveries with each other to maintain accuracy in methods and reporting. Infer what could happen if scientists did not compare results.

Figure 1.9 Scientists, like those shown in the photo, communicate data and discoveries with each other to maintain accuracy in methods and reporting. Infer what could happen if scientists did not compare results. Section 3 • Communication in Science 17

Royalty-free/CORBIS

Section 3 • Communication in Science 17

Royalty-free/CORBIS

Graphs By graphing data in a variety of ways, scientists can more easily show the relationships among data sets. Graphs also allow scientists to represent trends in their data. You will be asked to graph the results of many experiments and activities in this book. There are three types of graphs you will use in this book.

Line graphs A visual display that shows how two variables are related is called a line graph. As shown in Figure 1.10, on a line graph, the independent variable is plotted on the horizontal (x) axis, and the dependent variable is plotted on the vertical (y) axis.

Circle graphs To show a fixed quantity, scientists often use a circle graph, also called a pie graph. The circle represents the total and the slices represent the different parts of the whole. The slices are usually presented as percentages.

Bar graphs To represent quantitative data, bar graphs use rectangular blocks called bars. The length of the bar is determined by the amount of the variable you are measuring as well as the scale of the bar graph. See the Skillbuilder Handbook, page 951, for examples of all the types of graphs described above.

Models In some of the investigations, you will be making and using models. A scientific model is an idea picture, a system, or a mathematical expression that represents the concept being explained. While a model might not have all of the components of a given idea, it should be a fairly accurate representation.

»ATA ANALYSIS LAll

Based on Real Data*

### Make and Use Graphs

How can graphs help interpret data? The table shows the average surface temperature of Earth over the past 125 years. The data in the table are global, average surface temperatures, in kelvin, starting in the year 1880.

Think Critically

1. Construct a line graph from the average surface temperatures in the data table.

2. Convert each temperature from kelvin to degrees Celsius by subtracting 273 from each value. Place both on your graph.

3. Determine from your graph the average surface temperature for 1988 in degrees Celsius.

4. Extrapolate, in Celsius, what the average surface temperature will be in the year 2100 if this trend continues.

 Gas Volume v. Temperature 2 1

0 100 200 300 400 500 600 700 Temperature (K)

0 100 200 300 400 500 600 700 Temperature (K)

Figure 1.10 A line graph shows the relationship between two variables. Determine Based on this graph, what is the relationship between gas volume and temperature?

Figure 1.10 A line graph shows the relationship between two variables. Determine Based on this graph, what is the relationship between gas volume and temperature?

 Average Global Surface Temperatures Years Average surface temperature (K) 1880-1899 286.76 1900-1919 286.77 1 920 - 1 939 286.97 1 940 - 1 959 287.02 1 960 - 1 979 286.98 1 980 - 1 999 287.33 2000-2004 287.59

*Data obtained from Goddard Institute for Space Studies, NASA Goddard Space Flight Center

*Data obtained from Goddard Institute for Space Studies, NASA Goddard Space Flight Center

Models can change when more data are gathered. As shown in Figure 1.11, early astronomers thought that Earth was the center of the solar system. This model was changed as the result of observations of the motions of the Sun and the planets in the night sky. The observations showed that the planets in our solar system orbit the Sun.

### Theories and Laws

A scientific theory is an explanation based on many observations during repeated investigations. A scientific theory is valid only if it is consistent with observations, makes predictions that can be tested, and is the simplest explanation of observations. Like a scientific model, a theory can be changed or modified with the discovery of new data.

A scientific law is a principle that describes the behavior of a natural phenomenon. A scientific law can be thought of as a rule of nature, even though the cause of the law might not be known. The events described by a law are observed to be the same every time. An example of a scientific law is Newton's first law of motion, which states that an object at rest or in motion stays at rest or in motion unless it is acted on by an outside force. This law explains why Earth and other planets in our solar system remain in orbit around the Sun. Theories are often used to explain scientific laws.

In this book, you will communicate your observations and draw conclusions based on scientific data. You will also read that many of the models, theories, and laws used by Earth scientists to explain various processes and phenomena grow from the work of other scientists and sometimes develop from unexpected discoveries. Figure 1.11 Scientific models, like this ancient one of the solar system, are used to represent a larger idea or system. As scientists gather new information, models can change or be revised. Explain what is wrong with this model.

Figure 1.11 Scientific models, like this ancient one of the solar system, are used to represent a larger idea or system. As scientists gather new information, models can change or be revised. Explain what is wrong with this model.

Section 1.3 Assessment

Section Summary

I Scientists communicate data so others can learn the results, verify the results, examine conclusions for bias, and conduct new experiments.

I There are three main types of graphs scientists use to represent data: line graphs, circle graphs, and bar graphs.

I A scientific model is an accurate representation of an idea or theory.

I Scientific theories and scientific laws are sometimes discovered accidentally.

lane

Understand Main Ideas

1. iman4ffl!fl Explain what might happen if a scientist inaccurately reported data from his or her experiment.

2. Describe the difference between scientific theory and scientific law.

3. Apply Why is it important to compare your data from a lab with that of your classmates?

Think Critically

4. Interpret Why would a model be important when studying the solar system?

5. Explain when to use a line graph, a circle graph, and a bar graph.

CEZES^Earth Science

6. Research scientific laws and theories, and write a concise example of each.

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Section 3 • Communication in Science 19

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### Responses

• toivo rajam
How do you express numbers in scientific notation 0.00049386?
8 years ago
• Sandra
What would happen if a scientist inaccurately reported data from his experiment?
8 years ago
• david
How do the rates of heat absorption and release vary between soil and water?
8 years ago
• daniel konig
What are the three types of graphs scientists commonly use?
8 years ago
• barry
Why is there not one established way to conduct an investigation?
8 years ago
• PRIMROSE
Why is it important to use the metric system when conducting scientific investigations?
8 years ago