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  • Chapter

    The Dynamic Earth

    What does this photo show? Is it the strange surfaceof another planet? No. It shows the broken surfaceof a glowing lava flow. The hot, liquid lavaunderneath slowly cools and hardens into rock. Early in Earth'shistory, its surface probably looked much like this. Over time,the oceans and atmosphere formed, followed by l iv ing things.Today, Earth continues to change. In Chapter 2, you will learnabout Earth's formation and how Earth has changed in the past.You will also learn about natural cycles that continue to shapeEarth today.

    Organize Your Thoughts

    Dynamic earth



    Weather and climate


    Air pressure

    Goals for Learning

    Cycles of life

    Water Oxygen Carbon Nitrogen


    To describe the origins of Earth

    To identify and describe Earth's three major parts

    To describe how water, oxygen, and other elementsmove through the environment

    To define weather and climate

    To explain the changes that happen on Earth overshort and long time periods

  • Objectives

    After reading thislesson, you shouldbe able to+ describe how

    and when Earthformed

    + name conditionsthat made theyoung Earthunwelcomingto life

    + explain how someof the earliest lifeforms createda more livableplanet

    Life-supportsystemA system that provideseverything needed tostay alive

    DebrisThe remains ofsomething that wasdestroyed

    MoltenMelted into a liquid

    The Earth Forms

    The earth travels through the universe at about 107,000kilometers per hour. Some people have compared it to aspaceship. Like a spaceship, the earth has everything it takesto keep people alive. You can think of it as a giantlife-support system.

    The Solid EarthEarth was not always so welcoming to life, though. Scientistsbelieve Earth formed when gas and rocky debris circling thesun crashed together. This crash happened 4.6 billion years ago.Energy heated the new planet to high temperatures. Earth wasso hot, in fact, that its surface was molten, or liquid, rock.

    Over time, the earth began to cool. Its molten surface hardenedinto solid rock. Yet its interior kept some of that original heat.Imagine that you could hold the earth in your hands and pull itapart. You would see that it has three layers. Together they looksomething like the inside of a hard-boiled egg.


    Figure 2.1.1 The earth has three major layers.

    44 Chapter 2 The Dynamic Earth

  • CrustThe outer layer ofthe earth

    ContinentalcrustThe lighter crust thatmakes up the continents

    Oceanic crustThe heavier crust thatmakes up the oceanfloor

    MantleThe layer of the earth(hat surrounds the core

    CoreThe hot center ofthe earth

    VentA opening in the earththat lets out gases andother materials

    EruptionAn explosion frombeneath the earth'ssurface


    MeteoriteA piece of rock that hitsthe surface o) a planetor moon after travelingthrough space

    CometA ball of ice, rock, frozengases, and dust thatorbits the sun

    The surface layer of rock and soil is called the crust. It is likethe shell of the hard-boiled egg. Today, Earth's crust includeseverything from high mountains to deep ocean floors. Thereare two types of crust. The lighter kind, called continentalcrust, makes up the continents. The heavier kind, the oceaniccrust, forms the ocean floor.

    Below the crust is a rock layer called the mantle. Think of it asthe hard-boiled egg's white interior. Heat can make the mantlerock soften and move like warm butter.

    The final section of the lithosphere is a round hot center calledthe core. It is a bit like an egg yolk that is not quite cooked. Youwill learn more about the layers of the earth in Lesson 2.

    Gases and LiquidsOther major changes occurred as the earth cooled. Gasesescaping from millions of volcanoes and vents formed a layerof air around the earth. As these gases cooled, some of themformed the oceans. Even so, this was not an environment wherehumans could have survived. Volcanic eruptions, or explosionsfrom beneath the earth's surface, were violent. The air wastoxic, or poisonous, to life. Rocky meteorites and icy cometsbattered Earth's surface. Damaging rays from the sun addedto the dangerous conditions.


    Mt. Vesuvius, Italy's most famous volcano, erupted explosively inA.D. 79. Ash and hot rocks from the volcano quickly buried theRoman town of Pompeii. As a result, everyday life in Pompeii waspreserved for almost 1,700 years. Careful excavation of Pompeii hashelped historians learn many details about ancient Roman culture.

    The Dynamic Earth Chapter 2 45

  • BacteriaThe simplest organismsthat carry out all basiclife activities

    ExtremeophileA tiny organism thatlives in one of Earth'sharshest environments

    Extremeophileslive in the worstenvironmentson Earthforexample, extremeheat, cold, orpressure. Theending -philemeans "one thatloves." These lifeforms thrive inconditions that noother living thingcan stand.

    The First Life on EarthStill, life finally appeared on Earth. Tiny living things thatresembled bacteria emerged in Earth's warm oceans. Bacteriaare the simplest living things on Earth, made of a single cell.These early organisms could live without oxygen, a gas necessaryfor most life today. Some of them fed on chemicals in theenvironment. Others used hydrogen to make their own food.

    Today, similar bacteria-like organisms known as extremeophilesstill exist. They can thrive in Earth's harshest environments. Theylive in the hot springs of Yellowstone National Park. They arefound around hot vents deep in the ocean and far underground.They live inside the stomachs of cows and other animals. Theseorganisms help scientists understand how life existed early inEarth's history.

    Figure 2.1.2 These crabs and tube worms live in extreme conditionsnear an undersea vent. While they are not extremeophiles, they live insimilar conditions.

    46 Chapter 2 The Dynamic Earth

  • CyanobacteriaThe first organisms onEarth to use sunlight to

    make their own food;also known as blue-green algae

    Science JMyth

    Myth: Life is arecent additionto Earth.

    Fact: Life has beenon Earth for mostof its history. Fossilsof early life formshave been found inrocks that are 3.5billion years old.However, somescientists think thatlife first appearedon Earth about 3.8billion years ago.

    About 2 to 2.7 billion years ago, another form of life appearedon Earth: the first bacteria. These blue-green algae, orcyanobacteria, formed in shallow seas. With energy from thesun, they produced their own food. In the process, they releasedoxygen as a waste product. As the number of cyanobacteriagrew, they began to change the chemicals in the air. Instead oftoxic gases like methane and ammonia, the air became full ofoxygen. This was air that animals could breathe.

    Earth had changed from an unstable place too toxic for any life.It had solid surfaces, warm oceans, and oxygen-rich air. Theplanet now had the requirements for many different forms of life.

    Express Lab 2


    * safety goggles

    * lab coat or apron

    * cereal bowl

    * pie pan* small plastic or paper cup

    4 vinegar

    * red food coloring

    * spoon

    4 baking powder

    Procedure1. Put on safety goggles and

    a lab coat or apron.

    2. Place the bowl upsidedown in the pie pan.

    3. Fill the cup two-thirds fullwith vinegar. Add the foodcoloring and stir.

    4. Set the cup on top of thebowl, and add a spoonfulof baking powder.

    Analysis1. What caused the "lava" to

    flow out of this "volcano"?

    2. What happened tothe gases in the "lava"bubbles?

    The Dynamic Earth Chapter 2 47

  • Lesson 1 R E V I E W

    Word Bank





    On a sheet of paper, write the word from the Word Bank thatcompletes each sentence correctly.

    1. When Earth first formed, its surface was so hot it wasliquid, or _ , rock.

    2. For a long time, Earth's atmosphere was too , orpoisonous, for life to exist.

    3. The first life forms to use sunlight to make their own foodwere called _,

    On a sheet of paper, write the letter of the answer thatcompletes each sentence correctly.

    4. Earth is about 4.6 years old.

    A thousand B million C billion D tril l ion

    5. Earth's atmosphere was formed by gases escaping fromvents and .

    A meteors B the sun C earthquakes D volcanoes

    6. Earth's earliest life forms appeared in the .

    A oceans B land C air D volcanoes

    Critical ThinkingOn a sheet of paper, write the answers to the followingquestions. Use complete sentences.

    7. How did Earth form?

    8. What were some of the reasons the young Earth could notsupport life?

    9. What do today's extremeophiles have in common withEarth's earliest life forms?

    10. How did cyanobacteria change Earth's air?

    48 Chapter 2 The Dynamic Earth

  • Lesson Land, Water, and Air


    After reading thislesson, you shouldbe able to+ describe several

    effects of platemovement

    + name differentparts of thehydrosphere

    + name severalbenefits of theatmosphere

    LithosphereThe solid surface andinterior of the earth

    HydrosphereThe water layer of the earth

    AtmosphereThe layer of airsurrounding the earth

    BiosphereThe parts of the earth whereliving things are found

    Plate tectonicsThe study of plates andhow they move

    ContinentaldriftThe theory of howcontinents move over time

    Earth's life-support system still contains the three major partsdescribed in Lesson 1. The lithosphere is Earth's solid surfaceand interior. The hydrosphere is t


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