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1.1 What Is Earth Science?

Reading StrategyCategorizing As you read about thedifferent branches of Earth science, fill in thecolumn with the name of each branch and listsome of the things that are studied.

Key ConceptsWhat is the study of Earthscience?

How did Earth and thesolar system form?

Vocabulary◆ Earth science◆ geology◆ oceanography◆ meteorology◆ astronomy

The spectacular eruption of a volcano, the magnificent scenery of arocky coast, and the destruction created by a hurricane are all subjectsfor Earth science. The study of Earth science deals with many fasci-nating and practical questions about our environment. What forcesproduced the mountains shown on page 1? Why does our dailyweather change? Is our climate changing? How old is Earth? How isEarth related to the other planets in the solar system? What causesocean tides? What was the Ice Age like? Will there be another?

Understanding Earth is not an easy task because our planet is alwayschanging. Earth is a dynamic planet with a long and complex history.

Overview of Earth ScienceEarth science is the name for the group of sciences that deals with

Earth and its neighbors in space. Earth science includes many subdivi-sions of geology such as geochemistry, geophysics, geobiologyand paleontology, as well as oceanography, meteorology, andastronomy.

Units 1 through 4 focus on the science of geology, a wordthat means “study of Earth.” Geology is divided into twobroad areas—physical geology and historical geology.

Physical geology includes the examination of the materi-als that make up Earth and the possible explanations for themany processes that shape our planet. Processes below thesurface create earthquakes, build mountains, and produce vol-canoes. Processes at the surface break rock apart and create

geology a.

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d. e.

f. g. ??

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Figure 1 Scientists calledpaleontologists study fossils,which are signs of life in thedistant past, to find out how life-forms have changed through time. Posing Questions Whatquestions do you have about this fossil?

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FOCUS

Section Objectives1.1 Define Earth science.1.2 Describe the formation of

Earth and the solar system.

Build VocabularyWord Parts Ask students to use adictionary to determine the meaningsof the following word parts:geo- (Earth); astro- (outer space);-ology (study of); -ography (study of);-onomy (study of)Based on this discussion and their priorknowledge, have students predict themeaning of this section’s vocabularywords. Then, have students look up thewords in the Glossary to check theirpredictions and make any necessarycorrections. Meteorology will likelypresent a problem, with most studentspredicting that it is the study of meteors,rather than the study of the atmosphere.

Reading Strategya. Earth, earthquakes, mountains,volcanoes, Earth’s historyb. oceanographyc. composition and movements ofseawater, coastal processes, seafloortopography, marine lifed. meteorologye. atmosphere, weather, climatef. astronomyg. universe, solar system

INSTRUCT

Overview ofEarth ScienceBuild Reading LiteracyRefer to p. 216D in Chapter 8, whichprovides guidelines for comparingand contrasting.

Compare and Contrast Have studentscreate a table to compare and contrastphysical geology and historical geology.They should fill in their table as theyread the first part of this section. Areasto consider include the focus of eacharea and examples of what is studied.Visual

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Introduction to Earth Science 3

different landforms. Erosion by water, wind, and ice results in differ-ent landscapes. You will learn that rocks and minerals form in responseto Earth’s internal and external processes. Understanding the origin ofrocks and minerals is an important part of understanding Earth.

In contrast to physical geology, the aim of historical geology is tounderstand Earth’s long history. Historical geology tries to establish atimeline of the vast number of physical and biological changes thathave occurred in the past. See Figure 1. We study physical geologybefore historical geology because we must first understand how Earthworks before we try to unravel its past.

Unit 5 is devoted to oceanography. Oceanography integrates thesciences of chemistry, physics, geology, and biology. Oceanographersstudy the composition and movements of seawater, as well as coastalprocesses, seafloor topography, and marine life. See Figure 2.

Unit 6 examines the composition of Earth’s atmosphere. The com-bined effects of Earth’s motions and energy from the sun cause theatmosphere to produce different weather conditions. This, in turn, cre-ates the basic pattern of global climates. Meteorology is the study of theatmosphere and the processes that produce weather and climate. Likeoceanography, meteorology also involves other branches of science.

Unit 7 demonstrates that understanding Earth requires an under-standing of Earth’s position in the universe. The science of astronomy,the study of the universe, is useful in probing the origins of our ownenvironment. All objects in space, including Earth, are subject to thesame physical laws. Learning about the other members of our solarsystem and the universe beyond helps us to understand Earth.

Throughout its long existence, Earth has been changing. In fact, it ischanging as you read this page and will continue to do so. Sometimes thechanges are rapid and violent, such as when tornados, landslides, orvolcanic eruptions occur. Many changes, however, take place so grad-ually that they go unnoticed during a lifetime.

Formation of EarthEarth is one of nine planets that revolve around the sun. Our solarsystem has an orderly nature. Scientists understand that Earth andthe other planets formed during the same time span and from thesame material as the sun. The nebular hypothesis suggests thatthe bodies of our solar system evolved from an enormous rotatingcloud called the solar nebula. It was made up mostly of hydrogenand helium, with a small percentage of heavier elements. Figure 3 onpage 4 summarizes some key points of this hypothesis.

What are the two main areas of geology?

Figure 2 Oceanographers studyall aspects of the ocean—thechemistry of its waters, thegeology of its seafloor, the physicsof its interactions with theatmosphere, and the biology of its organisms.

Use CommunityResourcesThe USGS (United States GeologicalSurvey) has a network of regional officeswhere geologists study geologicalphenomena at local, regional, andglobal levels. Their activities includemonitoring earthquake activity,mapping subsurface rock formations,and providing the public with infor-mation about geologic events suchas floods and landslides. Ask a USGSgeologist from a local office to talk tothe class about what geologists do attheir jobs. Ask students to preparequestions in advance.Interpersonal

Formation of EarthBuild Reading LiteracyRefer to p. 186D in Chapter 7, whichprovides guidelines for relating textand visuals.

Relate Text and Visuals Have studentsturn ahead in the text to Figure 3 on p. 4for a visual representation of the nebularhypothesis. Have them read the figurecaption, then use the figure to describethe major steps in the nebular hypothesis.(Solar system begins as cloud of dust andgases. Cloud starts to rotate and collapse.Heated center forms the sun. Coolingcreates solid particles. Collisions createasteroid-sized bodies. Asteroids form theinner planets. Lighter materials and gasesform the outer planets.)Visual

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Customize for English Language Learners

Students should use the words and wordparts they just learned, along with their priorknowledge, to define the following words:oceanographer, meteorologist, geography,geologist, geological, astronaut, astronomer.

Students should then use a dictionary to checktheir definitions. Review the correct meaningsof these words with students when they arefinished.

Answer to . . .

The two main areas ofgeology are physical

geology and historical geology.

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Figure 3 Formation of the Solar System According to the Nebular Hypothesis A Our solar system began as anenormous cloud of dust and gases made up mostly of hydrogen and helium with a small percentage of heavier elements.B This cloud, called a nebula, started to rotate and collapse toward the center of the cloud. Heat was generated at thecenter, which eventually formed the sun. C Cooling of the nebula caused rocky and metallic materials to form tiny solidparticles. D Repeated collisions of these particles resulted in the formation of asteroid-sized bodies. E These asteroidseventually combined to form the four inner planets—Mercury, Venus, Earth, and Mars. The lighter materials and gasescombined farther away from the center to form the four outer planets—Jupiter, Saturn, Uranus, and Neptune.

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Use VisualsFigure 3 Have students study thediagram illustrating the nebularhypothesis. Ask: What do all stages ofthis hypothesis have in common? (Inall stages, the system is spinning.) Whatwas the first stage in the develop-ment of our solar system? (Our solarsystem began as an enormous cloud ofgas and dust.) Challenge students tomake a timeline or flowchart of thekey events in the formation of oursolar system. (Students should make atimeline or flowchart based on steps Athrough E given in the figure caption.)Visual, Logical

Separation and DensityPurpose Students see how substancesseparate based on density.

Materials 2 large glass jars with lids,100 mL sand, 100 mL rock salt, 100 mLsugar, 100 mL water, 100 mL vegetableoil, 100 mL corn syrup

Procedure At the start of the class,place all of the solids in one jar and allthe liquids in another jar. Put the lids onboth jars and shake them carefully. Letthe jars settle during the class. Then,have the students look at them. Ask:Why did the liquids separate?(Differences in density made the liquidsrise or fall and separate.) Why didn’t thesolids separate? (The solid particles wereunable to move past each other.) Whatstate was Earth most likely in when itseparated into layers? (The materialsthat made up Earth must have beenmolten or nearly molten.)

Expected Outcome The liquids willseparate into different layers. The solidswill remain mixed.Visual, Logical

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As Earth was forming, density differencescaused denser materials to sink to Earth’s core,while less dense materials escaped to theatmosphere. Density differences continue toshape Earth today. Today’s volcanic eruptionsare generally caused by less dense magma andgases rising up through the mantle until theypenetrate the crust, resulting in a volcanic

eruption. This is an example of the principleof uniformitarianism, which is essential to thestudy of geology. This principle states that theprocesses that exist on Earth today are identicalto the processes that existed on Earth in thedistant past. This principle allows geologiststo make useful inferences based oncontemporary observations.

Facts and Figures

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Section 1.1 Assessment

Reviewing Concepts1. What are the sciences that are included in

Earth science?

2. What topics are included in the study ofphysical geology?

3. Explain how physical geology differs fromhistorical geology.

4. Describe the nebular hypothesis.

Critical Thinking5. Forming Conclusions Explain why Earth is

called a dynamic planet.

6. Inferring Would meteorology be a usefulscience to apply to the study of planets suchas Mercury and Mars? Explain.

7. Hypothesizing Suppose that as Earthformed, all lighter elements were released tosurrounding space. How might this affect thestructure of Earth today?

High temperatures and weak fields of gravity characterized theinner planets. As a result, the inner planets were not able to hold ontothe lighter gases of the nebular cloud. The lightest gases, hydrogen andhelium, were whisked away toward the heavier planets by the solarwind. Earth, Mars, and Venus were able to retain some heavier gasesincluding water vapor and carbon dioxide. The materials that formedby outer planets contained high percentages of water, carbon dioxide,ammonia, and methane. The size and frigid temperatures of the outerplanets provided the surface gravity to hold these heavier gases.

Layers Form on Earth Shortly after Earth formed, the decay ofradioactive elements, combined with heat released by colliding particles,produced some melting of the interior. This allowed the denser elements,mostly iron and nickel, to sink to Earth’s center. The lighter, rocky com-ponents floated outward, toward the surface. This sinking and floatingis believed to still be occurring, but on a much smaller scale. As a resultof this process, Earth’s interior is not made of uniform materials. It con-sists of layers of materials that have different properties.

An important result of this process is that gaseous materials wereallowed to escape from Earth’s interior, just as gases escape todayduring volcanic eruptions. In this way, an atmosphere graduallyformed along with the ocean. It was composed mainly of gases thatwere released from within the planet.

Why does Earth have layers?

Introduction to Earth Science 5

Summarizing Earth science is composedof many different areas of study. Why is itimportant to include all of these areas inthe study of Earth and the solar system?

Build Science SkillsInferring Based on the information inthis section, ask students to infer whichof Earth’s layers will be the densest.Have students turn ahead in the text toFigure 6 on p. 8 to see a diagram ofEarth’s layers.Logical

ASSESSEvaluateUnderstandingTo assess students’ knowledge of sectioncontent, ask them to answer the KeyConcepts questions at the beginningof this section.

ReteachHave students use Figure 3 to explain intheir own words the formation of oursolar system.

Because Earth is an ever-changingplanet, all the spheres on Earth areinteractive and affect one another. Tounderstand Earth’s existence and history,it is important to study all aspects ofEarth together.

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Answer to . . .

Earth has layers becausedenser elements sank to

Earth’s center and less dense elementsfloated to the surface.

4. This hypothesis suggests that the solarsystem began as an enormous cloud of dustand gas. The cloud began to rotate, heat wasproduced, and the cloud began to collapsetoward the center. The sun formed at thecenter from this heat. Cooling of the cloudcaused rocky and metallic materials to formthe inner planets. The outer planets formedfrom lighter materials and gases.5. The surface of Earth is continually chang-ing due to its layered structure.

Section 1.1 Assessment

1. Earth science includes many subdivisionsof geology such as geochemistry, geophysics,geobiology, and paleontology, as well asmeteorology, oceanography, and astronomy.2. Physical geology includes processes thatoperate on and below Earth’s surface such asvolcanoes, mountain building, erosion, andearthquakes.3. Historical geology’s aim is to understandEarth’s history. Physical geology’s aim is tounderstand the processes that shape Earth.

6. It would not be very useful because thesetwo planets have only very thin atmospheres.Very few meteorological processes are occur-ring on them.7. If all the lighter elements were no longer apart of Earth’s structure, Earth probably wouldnot have layers defined by their density.

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Earth’s Place in the UniverseFor centuries, people who have gazed at the nightsky have wondered about the nature of the universe,Earth’s place within it, and whether or not we arealone. Today many exciting discoveries in astron-

omy are beginning to provide answers about theorigin of the universe, the formation and evolutionof stars, and how Earth came into existence.

14 b.y. 13 b.y. 10 b.y. 5 b.y. Present

BigBang

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Galaxies evolveand move apart Milky

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Figure 4 Big BangTheory Between 13 and14 billion years ago, ahuge explosion sent allof the universe’s matterflying outward at greatspeed. After a fewbillion years, thematerial cooled andcondensed into the firststars and galaxies.About 5 billion yearsago, our solar systembegan forming in agalaxy that is now calledthe Milky Way galaxy.

The realization that the universe is immense andorderly began in the early 1900s. Edwin Hubble andother scientists demonstrated that the Milky Waygalaxy is one of hundreds of billions of galaxies,each of which contains billions of stars. Evidencesupports that Earth, its materials, and all livingthings are the result of the Big Bang theory. The uni-verse began between 13 and 14 billion years ago as adense, hot, massive amount of material exploded withviolent force. See Figure 4. Within about one second,the temperature of the expanding universe cooled toapproximately 10 billion degrees. Basic atomic parti-cles called protons and neutrons began to appear.After a few minutes, atoms of the simplest elements—hydrogen and helium—had formed. The initialconversion of energy to matter in the young universewas completed.

During the first billion years or so, matter (essentiallyhydrogen and helium) in the expanding universeclumped together to form enormous clouds thateventually collapsed to become galaxies and clustersof galaxies. Inside these collapsing clouds, smaller con-centrations of matter formed into stars. One of thebillions of galaxies to form was the Milky Way.

During the life of most stars, energy produced ashydrogen nuclei (protons) fuses with other hydrogen

nuclei to form helium. During this process, callednuclear fusion, matter is converted to energy. Starsbegin to die when their nuclear fuel is used up.Massive stars often have explosive deaths. Duringthese events, called supernovas, nuclear fusion pro-duces atoms such as oxygen, carbon, and iron. Theseatoms may become the materials that make up futuregenerations of stars. From the debris scattered duringthe death of a preexisting star, our sun, and the solarsystem formed

Our star, the sun, is at the very least a second-generation star. Along with the planets in our solarsystem, the sun began forming nearly 5 billion yearsago from a large interstellar cloud called a nebula.This nebula consisted of dust particles and gasesenriched in heavy elements from supernova explo-sions. Gravitational energy caused the nebula tocontract, rotate, and flatten. Inside, smaller concen-trations of matter began condensing to form theplanets. At the center of the nebula there was suffi-cient pressure and heat to initiate hydrogen nuclearfusion, and our sun was born.

It has been said that all life on Earth is related to thestars. This is true because the atoms in our bodiesand the atoms that make up everything on Earth,owe their origin to a supernova event that occurredbillions of years ago, trillions of kilometers away.

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Earth’s Place inthe UniverseBackgroundThe Milky Way is a collection of severalhundred billion stars, the oldest ofwhich is about 10 billion years. It is oneof a cluster of approximately 28galaxies, called the Local Group, thatexists in our region of the universe.Initially, the oldest stars in the Milky Wayformed from nearly pure hydrogen.Later, succeeding generations ofyounger stars, including our Sun, wouldhave heavier, more complex atomsavailable for their formation.

Teaching Tips• As students read the feature and look

at Figure 4, have them make a timelineof the events shown from the bigbang to the present.

• While reading Earth’s Place in theUniverse feature, have students createa flowchart showing the chain ofevents starting with the big bang andending with the formation of our sunand the planets of our solar system.(Big Bang → Protons and neutronsappear → Hydrogen and helium form →Hydrogen and helium condense intoclouds → Galaxies and galaxy clustersform and start spreading apart →Clouds of gas and dust collapse, formingstars → Stars become supernovas →Nebula, enriched from supernovas,contracts, rotates, and flattens →Planets and our sun form)

Students may think that the Milky Wayis at the center of the universe. Theymay have inferred this from learningthat almost all galaxies are moving awayfrom the Milky Way in all directions. Todispel this misconception, have studentsmark with a black marker a number ofdots on a partially inflated balloon. Blowup the balloon and observe whathappens to the dots. They all moveaway from each other, as do almost allgalaxies. All points in the universe canbe thought of as being the center of theuniverse, as everything else is movingaway from everything else.Visual

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