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  • 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 Fieldsof Study? Art, architecture, philosophy, and science are all READING TOOLBOXexamples of fields of study. However, science has dif- Organize As you read, makeferent 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 theexist?” 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 naturalworld works by making observations and by doingexperiments. As they study the natural world, scientistsassume 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 twostand nature. That is, scientists assume that with the right assumptions that all scientists make?tools and correct methods, they can find the answersthey are looking for. There are many natural events thatscientists do not yet understand. Scientists assume thatthey will someday be able to understand these events. Scientists also assume that nature is predictable. Ingeneral, scientists observe patterns in nature. From theway a pattern repeats, scientists can predict that an eventwill 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 maypredict that when these same weather conditions happenagain, another tornado will form.Copyright © Holt McDougal. All rights reserved.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 solveLOOKING CLOSER scientific problems. The flowchart below shows one way2. Infer Why is there anarrow 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. A3. 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 orhypotheses? 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.Copyright © Holt McDougal. All rights reserved.Holt McDougal Earth Science 6 Introduction to Earth Science
  • 3. Name Class Date SECTION 2 Science as a Process continuedTESTING THE HYPOTHESIS After scientists form a hypothesis, they look for waysto test it in an investigation. In some investigations, thescientist will make more observations and see if they fitthe hypothesis. For example, a scientist may use toolsto study the movements of cool and warm air. He coulduse the measurements he takes to learn whether cool airmoves 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 experimenthas conditions or factors that can change. These factorsare called variables. There are two types of variables.Independent variables are factors that the scientistchanges. Dependent variables are factors that changeas a result of the independent variables. READING CHECK For example, suppose a scientist did an experiment to 4. Discuss What are twolearn 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. Thedependent variable is how much the plants grow. In thisexperiment, the scientist would change only the amountof water each plant gets. She would keep all other condi-tions, such as amount of sunlight, temperature, and typeof 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 supportthe 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, thescientists must throw out the hypothesis or change it.Unexpected results are important to science. They cancause scientists to ask new questions.Copyright © Holt McDougal. All rights reserved.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 mainreason 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 resultsLOOKING CLOSER7. Evaluate Methods Whatare two advantages thisphysical model has over the This scientist is workingactual 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.Copyright © Holt McDougal. All rights reserved.Holt McDougal Earth Science 8 Introduction to Earth Science
  • 5. Name Class Date SECTION 2 Science as a Process continuedHow Do Scientists Make AccurateMeasurements? Scientists gather information during investigations.Measurement is a very important method for gatheringinformation in most scientific investigations.SI UNITS Scientists need to be able to compare and analyze eachother’s results. Therefore, scientists around the world usea common system of measurement. The system is calledthe International System of Units, or SI. Meters andkilograms are examples of SI units. READING CHECK 8. Explain Why is theACCURACY AND PRECISION International System of Units important? Accuracy and precision are two ways to describe mea-surements. Accuracy describes how close a measurementis to the true value. Precision describes how exact a mea-surement is. For example, stating the length of a stringas 1 m is less precise than stating that the length of thestring 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 differencebetween accuracy and precision. LOOKING CLOSER 9. Infer If there wereGood 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 aretwo ways to express error: as a percentage error or as aconfidence interval.Copyright © Holt McDougal. All rights reserved.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 far10. Calculate You have a measured value is from the true value. You can usemade a meterstick out of the following equation to find the percentage error ofcardboard, but you’re notsure how accurate it is. You a measurement.measure your stick against areal meterstick. You find thatyour meterstick is only 90 cm percentage error ϭ [(actual value − measured value)] × 100 actual valuelong. What is your percentageerror? 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 themTalk About It are within 3 cm of this average length. The scientist mayCalculate As a class, make report the average length of all the ears of corn in thea list of shoe sizes. Discuss field as “23 Ϯ 3 cm with 90% confidence.”what confidence interval youcould use to discuss shoesizes. 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 out11. Define What happensduring 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.Copyright © Holt McDougal. All rights reserved.Holt McDougal Earth Science 10 Introduction to Earth Science
  • 7. Name Class Date SECTION 2 Science as a Process continuedDEVELOPING A THEORY After a scientist publishes his ideas and results, otherscientists typically test the hypothesis and build on theresults. The process of repeated testing may continue foryears. In time, the hypothesis may be proved incorrect,be changed, or be accepted by most scientists. When a hypothesis has been tested many times andbecomes accepted, the hypothesis may help form atheory. A theory is an explanation that is supported byall existing observations and study results. However, ifrepeated results from later tests do not support thetheory, scientists may need to change it. READING CHECK 12. Identify RelationshipsTHE 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 importantbecause discoveries in different fields may add supportto one idea. When an idea is supported by evidencefrom more than one field, the idea is more likely to beaccurate. The figure below shows one hypothesis that is basedon 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 thenatural 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, plasticscan cause pollution and harm wildlife. An understandingof 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.Copyright © Holt McDougal. All rights reserved.Holt McDougal Earth Science 11 Introduction to Earth Science
  • 8. Name Class DateSection 2 ReviewSECTION 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.Copyright © Holt McDougal. All rights reserved.Holt McDougal Earth Science 12 Introduction to Earth Science