8 The History of Life on Earth Compression guide: Chapter...

OBJECTIVES LABS, DEMONSTRATIONS, AND ACTIVITIES TECHNOLOGY RESOURCES

Compression guide:To shorten instructionbecause of time limitations,omit Section 3.

The History of Life on EarthChapter Planning Guide

OSP Lesson Plans (also in print) TR Bellringer Transparency* TR L27 Using Half-Lives to Date Fossils* TR L117 The Geologic Time Scale* TR L29 Moving Continents and

Tectonic Plates*CD Science Tutor

TE Activity Newspaper Layers, p. 195 ◆g

SE Connection to Social Studies A Place in Time,p. 196 ◆g

TE Group Activity Detailed Geologic Timeline, p. 196a SE Quick Lab Making a Geologic Timeline, p. 197 ◆g

CRF Datasheet for Quick Lab* TE Activity Rock Collectors, p. 197g SE Skills Practice Lab The Half-Life of Pennies,

p. 769 ◆g

CRF Datasheet for LabBook*

Section 1 Evidence of the Past• Explain how fossils can be formed and how their age

can be estimated.• Describe the geologic time scale and the way that

scientists use it.• Compare two ways that conditions for life on Earth

have changed over time.

OSP Lesson Plans (also in print) TR Bellringer Transparency* SE Internet Activity, p. 201g

CRF SciLinks Activity*g CD Interactive Explorations CD-ROM

Rock On!gCD Science Tutor

TE Connection Activity Earth Science, p. 201 ◆g

TE Activity Using Maps, p. 201 ◆g

TE Group Activity Ancient Plants, p. 202g TE Connection Activity Real World, p. 202 ◆g

LB Long-Term Projects & Research Ideas A Horse isa Horse*a

PACING • 45 min pp. 200–205Section 2 Eras of the Geologic

Time Scale• Outline the major developments that allowed life to

exist on Earth.• Describe the types of organisms that arose during the

four major divisions of the geologic time scale.

OSP Lesson Plans (also in print) TR Bellringer Transparency* TR L30 Comparison of Primate Skeletons*VID Lab Videos for Life ScienceCD Science Tutor

TE Activity Exploring Vision, p. 207g TE Activity Primate Characteristics, p. 208 ◆b

TE Group Activity Comparing Hominids, p. 208 ◆g

SE School-to-Home Activity Thumb Through This,p. 209g

TE Connection Activity Art, p. 209 ◆g

TE Activity Classifying Primates, p. 211a SE Inquiry Lab Mystery Footprints, p. 212 ◆g

CRF Datasheet for Chapter Lab* SE Science in Action Math, Social Studies, and Language

Arts Activities, pp. 218–219g

PACING • 90 min pp. 206–211Section 3 Humans and Other Primates• Describe two characteristics that all primates share.• Describe three major groups of hominids.

OSP Parent Letter ■

CD Student Edition on CD-ROM CD Guided Reading Audio CD ■

TR Chapter Starter Transparency*VID Brain Food Video Quiz

SE Start-up Activity, p. 193 ◆gpp. 192–199PACING • 90 minChapter Opener

CRF Vocabulary Activity*g SE Chapter Review, pp. 214–215g

CRF Chapter Review* ■g

CRF Chapter Tests A* ■g, B*a, C*s SE Standardized Test Preparation, pp. 216–217g

CRF Standardized Test Preparation*gCRF Performance-Based Assessment*gOSP Test Generator, Test Item Listing

CHAPTER REVIEW, ASSESSMENT, ANDSTANDARDIZED TEST PREPARATION

PACING • 90 min

Online and Technology Resources

Visit go.hrw.com foraccess to Holt OnlineLearning, or enter thekeyword HL7 Homefor a variety of freeonline resources.

This CD-ROM package includes:• Lab Materials QuickList Software• Holt Calendar Planner• Customizable Lesson Plans• Printable Worksheets

• ExamView® Test Generator• Interactive Teacher’s Edition• Holt PuzzlePro®

• Holt PowerPoint® Resources

191A Chapter 8 • The History of Life on Earth

8

STANDARDS CORRELATION SKILLS DEVELOPMENT RESOURCES SECTION REVIEW AND ASSESSMENT CORRELATIONS

CRF Directed Reading A* ■b, B*sIT Interactive Textbook* Struggling ReadersStruggling Readers

CRF Vocabulary and Section Summary* ■g

SE Reading Strategy Reading Organizer, p. 194g SE Math Practice Fractions of Fractions, p. 195g TE Support for English Language Learners, p. 195 TE Inclusion Strategies, p. 198 SE Connection to Geology Mid-Atlantic Ridge, p. 199g MS Math Skills for Science Radioactive Decay and the Half-Life*g MS Math Skills for Science Geologic Time Scale*gCRF Reinforcement Worksheet Earth Timeline*b

SE Reading Checks, pp. 195, 197, 198g TE Homework, p. 197g TE Reteaching, p. 198b TE Quiz, p. 198g TE Alternative Assessment, p. 199g SE Section Review,* p. 199 ■g

CRF Section Quiz* ■g

UCP 1, 2, 4; SAI 1, 2; HNS 1, 2,3; LS 1a, 3d, 5b, 5c; LabBook:UCP 1, 3; SAI 1; LS 5c

CRF Directed Reading A* ■b, B*sIT Interactive Textbook* Struggling ReadersStruggling Readers


SE Reading Strategy Mnemonics, p. 200g TE Support for English Language Learners, p. 201 SE Connection to Oceanography Prehistoric Marine Organisms,

p. 202g TE Inclusion Strategies, p. 202 SE Math Focus Relative Scale, p. 204g TE Connection to Math Another Time Scale, p. 204a MS Math Skills for Science Subtraction Review*gCRF Reinforcement Worksheet Condensed History*b

SE Reading Checks, pp. 200, 203, 204g TE Reteaching, p. 204b TE Quiz, p. 204g TE Alternative Assessment, p. 204g SE Section Review,* p. 205 ■g

CRF Section Quiz* ■

UCP 1, 2, 3, 4; SAI 1;LS 1a, 1b, 3d, 5a, 5b, 5c

CRF Directed Reading A*b, B*sIT Interactive Textbook* Struggling ReadersStruggling Readers


SE Reading Strategy Discussion, p. 206g TE Support for English Language Learners, p. 207

CRF Critical Thinking Fossil Revelations*a

SE Reading Checks, pp. 207, 208, 211g TE Homework, p. 210g TE Reteaching, p. 210b TE Quiz, p. 210g TE Alternative Assessment, p. 210a SE Section Review,* p. 211 ■ g

CRF Section Quiz* ■g

UCP 2, 4, 5; SAI 1, 2; ST 1, 2;HNS 2, 3; LS 1a, 3d, 5a, 5b, 5c;Chapter Lab: UCP 2, 5; SAI 1;HNS 2

SE Pre-Reading Activity, p. 192gOSP Science Puzzlers, Twisters & Teasersg

National ScienceEducation Standards

UCP 2, 3, SAI 1, 2; SPSP 5;HNS 3

CRF Chapter Resource File SS Science Skills Worksheets IT Interactive TextbookOSP One-Stop Planner MS Math Skills for Science Worksheets * Also on One-Stop Planner

SE Student Edition LB Lab Bank CD CD or CD-ROM ◆ Requires advance prepTE Teacher Edition TR Transparencies VID Classroom Video/DVD ■ Also available in Spanish

KEY

Maintained by the NationalScience Teachers Association.See Chapter Enrichment pagesthat follow for a complete listof topics.

www.scilinks.orgCheck out Current Sciencearticles and activities byvisiting the HRW Web siteat go.hrw.com. Just typein the keyword HL5CS08T.

• Lab Videos demonstratethe chapter lab.

• Brain Food Video Quizzeshelp students review thechapter material.

ClassroomVideos

Holt Lab GeneratorCD-ROM

Search for any lab by topic, standard,difficulty level, or time. Edit any labto fit your needs, or create your ownlabs. Use the Lab Materials QuickListsoftware to customize your labmaterials list.

• Guided Reading Audio CD(Also in Spanish)

• Interactive Explorations• Virtual Investigations• Visual Concepts• Science Tutor

ClassroomCD-ROMs

Chapter 8 • Chapter Planning Guide 191B

Planning ResourcesTEST ITEM LISTINGPARENT LETTERLESSON PLANS

Visual ResourcesCHAPTER STARTER

TRANSPARENCYBELLRINGER

TRANSPARENCIES

CONCEPT MAPPINGTRANSPARENCYTEACHING TRANSPARENCIES

TEACHING TRANSPARENCIES

TEST ITEM LISTING

Copyright © by Holt Rinehart and Winston All rights reserved

The World of ScienceMULTIPLE CHOICE

1. A limitation of models is thata. they are large enough to see.b. they do not act exactly like the things that they model.c. they are smaller than the things that they model.d. they model unfamiliar things.Answer: B Difficulty: I Section: 3 Objective: 2

2. The length 10 m is equal toa. 100 cm. c. 10,000 mm.b. 1,000 cm. d. Both (b) and (c)Answer: B Difficulty: I Section: 3 Objective: 2

3. To be valid, a hypothesis must bea. testable. c. made into a law.b. supported by evidence. d. Both (a) and (b)Answer: B Difficulty: I Section: 3 Objective: 2 1

4. The statement "Sheila has a stain on her shirt" is an example of a(n)a. law. c. observation.b. hypothesis. d. prediction.Answer: B Difficulty: I Section: 3 Objective: 2

5. A hypothesis is often developed out ofa. observations. c. laws.b. experiments. d. Both (a) and (b)Answer: B Difficulty: I Section: 3 Objective: 2

6. How many milliliters are in 3.5 kL?a. 3,500 mL c. 3,500, 000 mLb. 0.0035 mL d. 35,000 mLAnswer: B Difficulty: I Section: 3 Objective: 2

7. A map of Seattle is an example of aa. law. c. model.b. theory. d. unit.Answer: B Difficulty: I Section: 3 Objective: 2

8. A lab has the safety icons shown below. These icons mean that you should weara. only safety goggles. c. safety goggles and a lab apron.b. only a lab apron. d. safety goggles, a lab apron, and gloves.Answer: B Difficulty: I Section: 3 Objective: 2

9. The law of conservation of mass says the tot al mass before a chemical change isa. more than the total mass after the change.b. less than the total mass after the change.c. the same as the total mass after the change.d. not the same as the total mass after the change.Answer: B Difficulty: I Section: 3 Objective: 2

10. In which of the following areas might you find a geochemist at work?a. studying the chemistry of rocks c. studying fishesb. studying forestry d. studying the atmosphereAnswer: B Difficulty: I Section: 3 Objective: 2

TEACHER RESOURCE PAGE

Lesson Plan

Section: Waves

PacingRegular Schedule: with lab(s):2 days without lab(s):2 days

Block Schedule: with lab(s): 1 1/2 days without lab(s): 1 day

Objectives1. Relate the seven properties of life to a living organism.

2. Describe seven themes that can help you to organize what you learn aboutbiology.

3. Identify the tiny structures that make up all living organisms.

4. Differentiate between reproduction and heredity and between metabolismand homeostasis.

National Science Education Standards CoveredLSInter6: Cells have particular structures that underlie their functions.

LSMat1: Most cell functions involve chemical reactions.

LSBeh1:Cells store and use information to guide their functions.

UCP1:Cell functions are regulated.

SI1: Cells can differentiate and form complete multicellular organisms.

PS1: Species evolve over time.

ESS1: The great diversity of organisms is the result of more than 3.5 billion yearsof evolution.

ESS2: Natural selection and its evolutionary consequences provide a scientificexplanation for the fossil record of ancient life forms as well as for the strikingmolecular similarities observed among the diverse species of living organisms.

ST1: The millions of different species of plants, animals, and microorganismsthat live on Earth today are related by descent from common ancestors.

ST2: The energy for life primarily comes from the sun.

SPSP1: The complexity and organization of organisms accommodates the needfor obtaining, transforming, transporting, releasing, and eliminating the matterand energy used to sustain the organism.

SPSP6: As matter and energy flows through different levels of organization ofliving systems—cells, organs, communities—and between living systems and thephysical environment, chemical elements are recombined in different ways.

HNS1: Organisms have behavioral responses to internal changes and to externalstimuli.

This CD-ROM includes all of theresources shown here and thefollowing time-saving tools:

• Lab Materials QuickListSoftware

• Customizable lesson plans

• Holt Calendar Planner

•The powerfulExamView® TestGenerator

Chapter Resources

Dear Parent,

Your son's or daughter's science class will soon begin exploring the chapter entitled “The

World of Physical Science.” In this chapter, students will learn about how the scientific

method applies to the world of physical science and the role of physical science in the

world. By the end of the chapter, students should demonstrate a clear understanding of the

chapter’s main ideas and be able to discuss the following topics:

1. physical science as the study of energy and matter (Section 1)

2. the role of physical science in the world around them (Section 1)

3. careers that rely on physical science (Section 1)

4. the steps used in the scientific method (Section 2)

5. examples of technology (Section 2)

6. how the scientific method is used to answer questions and solve problems (Section 2)

7. how our knowledge of science changes over time (Section 2)

8. how models represent real objects or systems (Section 3)

9. examples of different ways models are used in science (Section 3)

10. the importance of the International System of Units (Section 4)

11. the appropriate units to use for particular measurements (Section 4)

12. how area and density are derived quantities (Section 4)

Questions to Ask Along the Way

You can help your son or daughter learn about these topics by asking interesting questions

such as the following:

• What are some surprising careers that use physical science?

• What is a characteristic of a good hypothesis?

• When is it a good idea to use a model?

• Why do Americans measure things in terms of inches and yards instead of centimeters

and meters ?

191C Chapter 8 • The History of Life on Earth

8

The History of Life on Earth CHAPTER STARTER

One day you and your friends learnabout a secret underground passage thatleads into an old abandoned mansion,and you set out to find it. As you walkaround a field in search of the passage,you stumble across a large hole in theground. Could this be it?

One by one, you and your friendssqueeze down into the hole. You slidedown the sloping tunnel andfinally land. Dusting yourself off,you turn on your flashlight.Instead of finding a passage toan abandoned mansion, you andyour friends find yourselves in animmense cavern. Painted high onthe cavern’s walls are pictures ofbulls, cows, horses, and stags. Youget the feeling these images havebeen here for a very long time.Who made these paintings?

This adventure actually occurred insouthern France in the late 1940s. Fourteenage boys went hunting for a passage-way to the old manor of Lascaux. Insteadof finding a passageway, they stumbledonto a 17,000-year-old connection withour ancestors, the Cro-Magnons. Three ofthe adventurers are shown below talkingto their teacher.

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Imagine . . .

The History of Life on Earth BELLRINGER TRANSPARENCY


Section: Evidence of the PastImagine that you haven’t cleaned your room for 30years and you finally decide to sort through the 2 mpile of stuff on your floor. What might you find onthe top of the pile? in the middle? on the bottom?

Write your responses in your science journal.

Section: Eras of the Geologic Time ScaleSuppose that electrical energy had never beendeveloped. How would your life differ from what it islike now? What do you do every day that requireselectricity?

Write your answers in your science journal.

Using Half-Lives to Date Fossils


TEACH

ING

TRA

NSPA

REN

CY

Amount of unstable atoms (mg)

Time

1half-life

2half-lives

3half-lives

21

0.5 4

Rockform

s

A

B

CD

AThe unstable atom

s in this sample

of rock have a half-life of 1.3 billionyears. The sam

ple contained 4 mg

of unstable atoms w

hen it formed.

After 1.3 billion years, (one half-

life for this type of unstable atom),

2 mg of the unstable atom

s havedecayed to becom

e stable atoms,

and 2 mg of unstable atom

s remain.

After 2.6 billion years (tw

o half-livesfor this sam

ple), the rock sample

contains 3 mg of stable decay

atoms and 1 m

g of unstable atoms.

After three half-lives, only 0.5 m

g ofunstable atom

s remain in the rock

sample. This is equal to one-eighth

of the original amount.

BCDA

toms of unstable

element

Atom

s of stabledecay product

L27

Moving Continents and Tectonic PlatesTEACHING TRANSPARENCY


PANTHALASSAOCEAN

NorthAmerica

SouthAmerica

Eurasia

Africa

India

Antarctica

Australia

PA

NG

AE

A

PA

N G A E A

The continents have been slowly moving throughout the history of Earth. The colored areas show the location of the continents 245 million years ago, and blue outlines show where the continents are today.

L29

SouthAmerican

plate

Africanplate

The continents ride on tectonic plates, outlined here in black. The plates are still moving about 1 to 10 cm per year.

The Geologic Time ScaleTEACHING TRANSPARENCY


Tertiary 65.5

Precambrian time

Era Period Time*

Cenozoic era

Mesozoic era

Jurassic 200

Triassic 251Paleozoic era

Carboniferous 359

Devonian 416

Silurian 444

Ordovician 488

Cambrian 542

Quaternary 1.8

Cretaceous 146

Permian 299

4,600

*indicates how many millions of years ago the period began

L117 Comparison of Primate SkeletonsTEACHING TRANSPARENCY


The gorilla pelvis tilts the ape’s largerib cage and heavy neck and headforward. The gorilla spine is curvedin a C shape. The arms are long toprovide balance on the ground.

The bones of gorillas (a type of ape) andhumans (a type of hominid) have a verysimilar form, but the human skeleton isadapted for walking upright.

The human pelvisis vertical and helpshold the entireskeleton upright.The human spineis curved in an Sshape. The arms areshorter than the legs.

L30

from thefrom thefrom the from the

divisions arebased on

the fossil records of

using

Cenozoic

plants

is an outline of Earth’shistory created by

era

The History of Life on Earth CONCEPT MAPPING


Use the following terms to complete the concept map below:geologic time scale, mammals, Mesozoic, paleontologists, eukaryotes,relative dating, absolute dating, Paleozoic, dinosaurs, Precambrian

The Tectonic Plates; Close-up of a Tectonic Plate


TEACH

ING

TRA

NSPA

REN

CY

This image show

s what you m

ight see if youcould lift the South A

merican plate out of its

position between other tectonic plates.

Oceaniccrust

Man

tle

Andes m

ountain range

Continental

crust

E20

Chapter: Plate Tectonics

SAMPLE SAMPLE SAMPLE

Meeting Individual Needs

Review and Assessments

Labs and Activities

DIRECTED READING A VOCABULARY ACTIVITY REINFORCEMENT

STANDARDIZED TEST PREPARATIONCHAPTER TEST BCHAPTER REVIEWSECTION QUIZ

SCILINKS ACTIVITY

MARINE ECOSYSTEMS

Go to www.scilinks.com. To find links relatedto marine ecosystems, type in the keywordHL5490. Then, use the links to answer thefollowing questions about marine ecosys-tems.

1. What percentage of the Earth’s surface iscovered by water?

2. What percentage of the Earth’s water is found in the oceans?

3. What is the largest animal on Earth?

4. Describe an ocean animal.

Name Class Date

SciLinks ActivityActivity

Developed and maintained by theNational Science Teachers Association

Topic: Reproductive SystemIrregularitiesSciLinks code: HL5490


Name Class Date

Vocabulary ActivityActivity

Getting the Dirt on the SoilAfter you finish reading Chapter: [Unique Title], try this puzzle! Use the clues belowto unscramble the vocabulary words. Write your answer in the space provided.

1. the breakdown of rock intosmaller and smaller pieces:AWERIGNETH

2. layer of rock lying beneath soil:CROKDEB

3. type of crop that is plantedbetween harvests to reduce soilerosion: CROVE

4. action of rocks and sedimentscraping against each other andwearing away exposed surfaces:SABRONIA

5. a mixture of small mineral frag-ments and organic matter: LISO

6. rock that is a source of soil:PRATEN CORK

7. type of reaction that occurs whenoxygen combines with iron toform rust: oxidation

8. type of weathering caused byphysical means: CLEMANIACH

9. the chemical breakdown of rocksand minerals into new substances: CAMILCHETHEARIGWEN

10. layers of soil, to a geologist:SNORHIZO

11. the uppermost layer of soil:SPOTOIL

12. process in which rainwater car-ries dissolved substances fromthe uppermost layers of soil to thebottom layers: HELANCIG

13. small particles of decayed plantand animal material in soil:MUUSH

14. the process in which wind, water,or ice moves soil from one location to another: ROOSINE

15. the methods humans use to takecare of soil:OSIL VASETONRICON

LONG-TERM PROJECTS & RESEARCH IDEAS

VOCABULARY AND SECTION SUMMARY


Section: EnergIn the space provided, write the letter of the description that best matches theterm or phrase.

______ 1. building molecules that can be used asan energy source. or breaking down moleculesin which energy is stored

______ 2. the process by which light energy is convertedto chemical energy

______ 3. an organism that uses sunlight or inorganicsubstances to make organic compounds

______ 4. an organism that uses sunlight or inorganicsubstances to make organic compounds

______ 5. an organism that consumes food to get energy

______ 6. the process of getting energy from food

In the space provided, write the letter of the term or phrase that best completeseach statement or best answers each question.

Name Class Date

Section QuizAssessment

a. photosynthesis

b. autotroph

c. heterotroph

d. cellular respiration

e. metabolism

f. cellular respiration

______ 7. Which of the following mostclosely resembles cellularrespiration?a. warm water moving

through copper pipesb. people movimg alomg a

escalatorc. mixing different foods in

a blenderd. logs burning in a fire

______ 8. An organism’s reproductivecells, such as sperm or eggcells, are called?a. genesb. chromosomesc. gamates.d. zygotes.

______ 9. An organism’s reproductivecells, such as sperm or eggcells, are called?a. genesb. chromosomesc. gamates.d. zygotes.

______10. Which of the following mostclosely resembles cellularrespiration?a. warm water moving

through copper pipesb. people movimg alomg a

escalatorc. mixing different foods in

a blenderd.

logs burning in a fire


Section: ExploringTHAT’S SCIENCE!

1. How did James Czarnowski get his idea for the penguin boat, Proteus?Explain.

2. What is unusual about the way that Proteus moves through the water?

MATTER + AIR ➔ PHYSICAL SCIENCE

3. What do air, a ball, and a cheetah have in common?

4. What is one question you will answer as you explore physical science?

5. Chemistry and physics are both fields of . Chemists

study the different forms of and how they interact.

and how it affects are

studied in physics.

Identify the field of physical science to which each of the following descriptionsbelongs by writing physics or chemistry in the space provided.

_______________________ 6. how a compass works

_______________________ 7. why water boils at 100°C

_______________________ 8. how chlorine and sodium combine to form table salt

_______________________ 9. why you move to the right when the car you are inturns left

Directed Reading A

Name Class Date

Skills Worksheet

DIRECTED READING B

Section: ExploringTHAT’S SCIENCE!

1. How did James Czarnowski get his idea for the penguin boat, Proteus?Explain.

2. What is unusual about the way that Proteus moves through the water?

MATTER + AIR ➔ PHYSICAL SCIENCE

3. What do air, a ball, and a cheetah have in common?

Directed Reading B

Name Class Date

Skills Worksheet

Section: UniqueVOCABULARY

In your own words, write a definition of the following term in the space provided.

1. scientific method

2. technology

3. observation

Name Class Date

Vocabulary & NotesSkills Worksheet

Name Class Date

ReinforcementSkills Worksheet

The Plane TruthComplete this worksheet after you finish reading the Section: [Unique SectionTitle]

You plan to enter a paper airplane contest sponsoredby Talkin’ Physical Science magazine. The personwhose airplane flies the farthest wins a lifetime sub-scription to the magazine! The week before the con-test, you watch an airplane landing at a nearbyairport. You notice that the wings of the airplane haveflaps, as shown in the illustration at right. The paperairplanes you’ve been testing do not have wing flaps.What question would you ask yourself based on these observations? Write yourquestion in the space below for “State the problem.” Then tell how you could usethe other steps in the scientific method to investigate the problem.

1. State the problem.

2. Form a hypothesis.

3. Test the hypothesis.

4. Analyze the results.

5. Draw conclusions.

Flaps


CRITICAL THINKING

SECTION REVIEW

Section: UniqueKEY TERMS

1. What do paleontologist study?

2. How does a trace fossil differ from petrified wood?

3. Define fossil.

UNDERSTANDING KEY IDEAS

Name Class Date

Section ReviewSkills Worksheet


[UniqueMULTIPLE CHOICE


______ 1. Surface currents are formed by a. the moon’s gravity. c. wind.b. the sun’s gravity. d. increased water density.

______ 2. When waves come near the shore, a. they speed up. c. their wavelength increases.b. they maintain their speed. d. their wave height increases.

______ 3. Longshore currents transport sediment a . out to the open ocean. c. only during low tide.b. along the shore. d. only during high tide.

______ 4. Which of the following does NOT control surface currents?a. global wind c. Coriolis effectb. tides d. continental deflections

______ 5. Whitecaps break a. in the surf. c. in the open ocean.b. in the breaker zone. d. as their wavelength increases.

______ 6. Most ocean waves are formed by a . earthquakes. c. landsides.b. wind. d. impacts by cosmic bodies.

______ 7. Which factor controls surface currents? a. global winds c. continental deflectionb. the Coriolis effect d. all of the above

______ 8. Streamlike movments of ocean water far below the surface arecalleda. jet currents c. surface currents.b. Coriolis currents. d. deep currents.

______ 9. When the sunlit part of the moon that can be seen from Earthgrows larger, it is a. waxing. c. in the new moon phase.b. waning. d. in the full moon phase.

______10. The Milky Way is thought to be a. an elliptical galaxy. c. a spiral galaxy.

Name Class Date

Chapter Test BAssessment


READING

Read the passages below. Then, read each question that follows the passage.Decide which is the best answer to each question.

Passage 1 adventurous summer camp in the world. Billy can’twait to head for the outdoors. Billy checked the recommendedsupply list: light, summer clothes; sunscreen; rain gear; heavy,down-filled jacket; ski mask; and thick gloves. Wait a minute! Billythought he was traveling to only one destination, so why does heneed to bring such a wide variety of clothes? On further investiga-tion, Billy learns that the brochure advertises the opportunity to“climb the biomes of the world in just three days.” The destinationis Africa’s tallest mountain, Kilimanjaro.

______ 1. The word destination in this passage means A camp B vacation.C place. D mountain.

______ 2. Which of the following is a FACT in the passage? F People ski on Kilimanjaro.G Kilimanjaro is Africa’s tallest mountain.H It rains a lot on Kilimanjaro.J The summers are cold on Kilimanjaro.

______ 3. Billy wondered if the camp was advertising only one destination afterhe read the brochure, which said thatA the camp was the most adventurous summer camp in the world. B he would need light, summer clothes and sunscreen.C he would need light, summer clothes and a heavy, down-filled

jacket.D the summers are cold on Kilimanjaro.

Name Class Date

Standardized Test PreparationAssessment

PERFORMANCE-BASEDASSESSMENT

OBJECTIVEDetermine which factors cause some sugar shapes to break down faster than others.

KNOW THE SCORE!As you work through the activity, keep in mind that you will be earning a gradefor the following:

• how you form and test the hypothesis (30%)

• the quality of your analysis (40%)

• the clarity of your conclusions (30%)

ASK A QUESTIONSWhy do some sugar shapes erode more rapidly than others?

MATERIALS AND EQUIPMENT

Name Class Date

Performanced-Based AssessmentAssessment SKILL BUILDER

Using Scientific Methods

• 1 regular sugar cube • 90 mL of waterCopyright © by Holt, Rinehart and Winston. All rights reserved.

USING VOCABULARY

1. Define biome in your own words.

2. Describe the characteristics of a savanna and a desert.

3. Identify the relationship between tundra and permafrost.

4. Compare the open-water zone and the deep-water zone.

5. Use each of the following terms in an original sentence: plankton, littoralzone, and estuary.

6. Describe how marshes and swamps differ.

Name Class Date

Chapter ReviewSkills Worksheet

SCIENCE PUZZLERS, TWISTERS & TEASERS

CHAPTER TEST A






______ 4. Which of the following does NOT control surface currents?a global wind c Coriolis effect

Name Class Date

Chapter Test AAssessment

CHAPTER TEST C






______ 4. Which of the following does NOT control surface currents?a global wind c Coriolis effect

Name Class Date

Chapter Test CAssessment

For a preview of available worksheets covering math and science skills, see pages T26–T33. All of these resources are also on the One-Stop Planner®.

Chapter 8 • Chapter Resources 191D

An Ancient Ancestor1. All animals living today are descendants of ancient animals.

Some of these animals looked different from their moderndescendants. Pick a modern mammal, and trace its evolu-tion. Illustrate its evolution using a family tree. How doesthe modern animal differ from its ancient ancestor? Whatother animals have evolved from the same common ances-tor? Create a poster of your findings.

Other Research Ideas2. Have you ever found a fossil of a plant or animal? Are

you interested in the Earth’s ancient past? Maybe youwould enjoy being a paleontologist! Research the career of a paleontologist, such as Charles Walcott, O. C. Marsh,or E. D. Cope. Write a paper about the paleontologist’s lifeand contributions to the field.

3. Should we do everything possible to protect a species fromextinction? Will extinction occur no matter what humansdo? Research this debate. Form an opinion and write aposition paper defending your opinion. Be sure to includeexamples of controversial efforts to protect endangeredspecies such as the spotted owl.

4. Did a comet kill the dinosaurs? In 1980, Luis Alvarezhypothesized that every 26 million years an unknowncelestial object passes near our solar system, bringing alonga host of comets. According to this theory, whenever thisobject approaches, comets bombard the Earth. The result ismass destruction and extinction of many species. Researchthe evidence Alvarez used to develop this theory. Write amagazine article about your findings.

Long-Term Project Idea5. Which part of the history of life on Earth do you find

most interesting? Visit a local museum or an on-line nat-ural history museum. Take a look at the exhibits about thehistory of the Earth. Create either a video documentary ora series of short articles about your favorite exhibits. Inyour presentation, be sure to explain the scientific infor-mation in each exhibit.

USEFUL TERM

paleontologista scientist who studiesthe fossil record

Name ___________________________________________________ Date _________________ Class _____________

STUDENT WORKSHEET8

A Horse Is a Horse

PROJECT

Horses haven’t always had hooves. In the tropical forests of the Eocene epoch, amany-toed creature about the size of a dog fed on soft tree leaves. Scientists call itHyracotherium, but we also know it as Eohippus, the dawn horse. Hyracotherium wasan ancient ancestor of the modern horse.

Scientific Sleuthing1. Each of the statements below was made by an organism during

the era in which it evolved. Write the correct era in the space provided. The organisms evolved during the following eras:Precambrian, Paleozoic, Mesozoic, or Cenozoic.a. I’ve seen the greatest swimmers of my generation destroyed.

b. People often accuse me of monkeying around.

c. Oxygen? What is that?

d. Smoke and flames have frightened me ever since the day alarge meteorite came crashing into my backyard.

e. My mother had to settle for a potted plant instead of flowers

Name _______________________________________________ Date ________________ Class______________

SCIENCE PUZZLERS, TWISTERS & TEASERS8

The History of Life on Earth

CHAPTER

A Solar Solution

Name Class Date

Critical Thinking Skills Worksheet

Joseph D. Burns

Inventors’ Advisory Consultants

Portland, OR 97201

Dear Mr. Burns,I’ve got this great idea for a new product called the BlissHeater. It’s a portable, solar-powered space heater. The heater’s design includes these features:•T

he heater will be as longas an adult’s arm and aswide as a

packing box.

•T

he heater will have aglass top set at an angleto catch the sun’s rays.

•T

he inside of the heaterwill be dark colored toabsorb solar heat.If you think my idea will work, I will make the Bliss

Heaters right away without wasting time and money on test-ing and making models. Please write back soon with youropinion.SPECIAL NEEDS

GENERAL

GENERAL

GENERAL

GENERAL

GENERAL

GENERAL

GENERAL

GENERAL SPECIAL NEEDS

GENERAL

GENERAL

SAMPLE

SAMPLE SAMPLE

SAMPLE SAMPLE

SAMPLE

SAMPLE

SAMPLE

SAMPLESAMPLE

SAMPLE

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SAMPLE

DATASHEETS FOR QUICKLABS

DATASHEETS FOR QUICK LABS


Name Class Date

Reaction to StressQuick Lab DATASHEET FOR QUICK LAB

BackgroundThe graph below illustrates changes that occur in the membrane potential of aneuron during an action potential. Use the graph to answer the followingquestions. Refer to Figure 3 as needed.

Analysis1. Determine about how long an action potential lasts.

SAMPLE

DATASHEETS FORCHAPTER LABS

Teacher’s NotesTIME REQUIRED

One 45-minute class period.

RATINGTeacher Prep–3Student Set-Up–2Concept Level–2Clean Up–2

MATERIALS

The materials listed on the student page are enough for a group of 4–5 students.Large, dried beans of any kind will work well in this exercise.

SAFETY CAUTION

Remind students to review all safety cautions and icons before beginning this labactivity.

Using Scientific MethodsSkills Practice Lab DATASHEET FOR CHAPTER LAB


1 2 3 4Easy Hard

Jason MarshMontevideo High

and Country School

SAMPLE

DATASHEETS FORLABBOOK

Teacher’s NotesTIME REQUIRED

One 45-minute class period.

Does It All Add Up?Skills Practice Lab DATASHEET FOR LABBOOK LAB


Jason MarshM t id Hi h

SAMPLE

Law of Superposition• The law of superposition states that in a series of

undisturbed sedimentary rock layers, each layer is older than the one above it and younger than the one below it. This law is based on an observation made by Nicolaus Steno, a Danish physician, in 1669.

Methods of Absolute Dating• Radioisotope dating is the most widely used method

for dating a fossil. This method analyzes samples of igneous rock found within the same rock formation as the fossil. The method differs depending on the type of chemical isotope analyzed. The older the rocks are, the less accurate the dating. Isotopes with shorter half-lives provide a more accurate range of possible ages for younger rocks and fossils. Radiocarbon dating by accelerator mass spectrometry (AMS) has become a preferred method to date with high accuracy carbon-based fossils less than 60,000 years old.

Is That a Fact!◆ The beginning of the Paleozoic era is sometimes

called the Cambrian explosion. Within the first 100 million years of this period, a large variety of multicellular organisms appeared for the first time on Earth, including most of the major groups of animals.

Modern Mass Extinction• Because of natural selection, there will always be some

extinctions of species within any given time period. Mass extinctions, however, are periods of acceleration of the average rate of extinction. Many scientists think that our planet has entered another era of mass extinc-tion and that human activities are prompting these extinctions. Species all over the Earth are threatened by habitat destruction, pollution, and invasive nonna-tive species. During the last 200 years, more than 50 species of birds, more than 75 species of mammals, and hundreds of other species have become extinct.

Chapter Enrichment

This Chapter Enrichment provides relevant and

interesting information to expand and enhance

your presentation of the chapter material.

Evidence of the PastPaul Sereno• Paul Sereno has traveled around the world to study

and document dinosaur fossils. He teaches at the University of Chicago and also involves his students in searching museum collections and combing deserts for new fossils. Sereno’s teams have made many impor-tant finds. One of the first was in 1988 in Argentina, where his team unearthed the skeletons of a primitive 12-foot-long dinosaur called Herrerasaurus. The fossils in that area shed light on how and when the Age of Reptiles began. Sereno has continued to map the dino-saur family tree by studying fossils in the Sahara, in Niger, and in Morocco.

Fossils• Fossils may be mere traces

of organisms. Preserved footprints, feces, gnaw marks, and dug-out holes can all be considered fossils. Also, traces or remains of organisms can be preserved in materials other than sedi-mentary rock,such as amber, tar, or lava.

• Despite what many people think, fossils are not diffi-cult to find. Nearly every state in the United States contains an abundance of fossils. However, scientists think that only a tiny fraction of the countless organ-isms that lived on Earth has been preserved as fossils. Many organisms have lived and died without leaving evidence of their existence in the fossil record.

Is That a Fact!◆ The oldest fossils known are structures called stro-

matolites that are more than 3.5 billion years old. These structures are bands of sedimentary rock that are very similar to layered mats formed today by colonies of bacteria and cyanobacteria.

8

191E Chapter 8 • The History of Life on Earth

Eras of the Geologic Time ScaleExperiment About the Origin of Life• In 1953, American scientist

Stanley Miller devised a famous experiment to simulate life-forming conditions on the early Earth. He mixed together hydrogen, ammonia, and methane (to repre-sent the air) and water (to represent the oceans) in a flask. When he applied electricity to the mixture, amino acids were produced. His experiment demonstrated that the building blocks of life could be created on Earth through simple chemistry. Scientists have since found amino acids in meteorites, confirming that con-ditions favorable for their formation also exist elsewhere.

Dinosaur Whodunit• Scientists continue to debate various hypotheses

about the cause of the mass extinction that wiped out the dinosaurs at the end of the Cretaceous period of the Mesozoic era. The prime suspect for many scien-tists is an asteroid that created the 185 km wide Chicxulub crater in the Yucatán area of the Gulf of Mexico. Seismology studies support this hypothesis. However, a sample of rock from the core of this crater contains evidence that the Chicxulub asteroid did not result in sudden climate change. An alternative hypothesis is that a series of asteroid impacts even-tually caused climate changes that led to the mass extinction.

Is That a Fact!◆ Dinosaurs are not the biggest animals ever to have

lived on Earth. Blue whales are bigger than the largest known dinosaur.

Humans and Other PrimatesClues to Migration Route• Scientists think that people passed

through the Nile Valley of Egypt when they migrated from Africa, perhaps as early as 100,000 years ago. The first evidence supporting this idea was an adundance of fossil tools and other arti-facts in the Nile Valley area. Then, in 1994, the team of Belgian archaeologist Pierre Vermeersch found an ancient—but clearly human—skeleton in the area. The skeleton appears to have been a child that was ritually buried over 80,000 years ago. The skull and teeth show similarities to those of equally old human remains from East Africa and the Middle East. These similarities show a link between the African and the Middle Eastern populations.

Dawn of Language• Scientists Matt Cartmill and Richard Kay examined

fossil hominid skulls and measured the hole through which the hypoglossal nerve passes in its course from the brain to the tongue. The hypoglossal nerve enables precise control over the tongue movements needed for speech. A large hole suggests a larger nerve. Chimpanzees have much smaller holes in their skulls than do modern humans. Because australopithecine skulls have small holes, like the skulls of chimpanzees, Cartmill and Kay think that australopithecines were unable to form words.

SciLinks is maintained by the National Science Teachers Association to provide you and your students with interesting, up-to-date links that will enrich your classroom presentation of the chapter.


Topic: Evidence of the PastSciLinks code: HSM0545

Topic: Fossil RecordSciLinks code: HSM0615

Topic: Mass ExtinctionsSciLinks code: HSM0916

Topic: Geologic Time ScaleSciLinks code: HSM0669

Topic: Birds and DinosaursSciLinks code: HSM0169

Topic: Human EvolutionSciLinks code: HSM0769

Visit www.scilinks.org and enter the SciLinks code for more information about the topic listed.

For background information about teaching strategies and

issues, refer to the Professional Reference for Teachers.

OverviewIn this chapter, students willlearn about the evidence of thehistory of life on earth. Studentswill study the geologic timescale and theories about theevolution of hominids.

Assessing PriorKnowledgeStudents should be familiarwith the following topics:

• cells

• the basic chemistry of life

• classification

• evolution

IdentifyingMisconceptionsAs students learn the material inthis chapter, they may have mis-conceptions about the length oftime living organisms have beenon Earth and the length of timeneeded for geologic processes.For example, mass extinctionsare “sudden” on a geologic timescale but may take thousands ofyears. Furthermore, studentsmay have misconceptions abouthow long humans have been onEarth. Students may also beunaware of the large amountof evidence scientists havegathered in order to determinethe time and order of eventsin Earth’s history.

National Science Education Standards

The following codes indicate the National Science EducationStandards that correlate to this chapter. The full text of thestandards is at the front of the book.

Chapter OpenerUCP 2, 3; SAI 1, 2; SPSP 5; HNS 3

Section 1 Evidence of the PastUCP 1, 2, 4; SAI 1, 2; HNS 1, 2, 3; LS 1a, 3d, 5b, 5c;LabBook: UCP 1, 3; SAI 1; LS 5c

Section 2 Eras of the GeologicTime ScaleUCP 1, 2, 3, 4; SAI 1; LS 1a, 1b, 3d, 5a, 5b, 5c

Section 3 Humans and Other PrimatesUCP 2, 4, 5; SAI 1, 2; ST 1, 2; HNS 2, 3; LS 1a, 3d, 5a, 5b, 5c

Chapter LabUCP 2, 5; SAI 1; HNS 2

Chapter ReviewLS 1a, 1b, 3d, 5a, 5b, 5c

Science in ActionUCP 2; ST 2; SPSP 5; HNS 1, 3

Standards Correlations

192 Chapter 8 • The History of Life on Earth

8

PRE-READINGPRE-READING

The History of Life on Earth

About the

What is 23,000 years old and 9 ft tall? Thepartial remains of the woolly mammoth inthis picture! The mammoth was found in thefrozen ground in Siberia in 1999. Scientiststhink that several types of woolly mammothsroamed the northern hemisphere until about4,000 years ago.

Layered Book Beforeyou read the chapter,create the Foldnote enti-

tled “Layered Book” described in theStudy Skills section of the Appendix.Label the tabs of the layered book with“Precambrian time,” “Paleozoic era,”“Mesozoic era,” and “Cenozoic era.”As you read the chap-ter, write informationyou learn about eachcategory under theappropriate tab.

SECTION

Geologic evidence allows usto understand the evolutionof life on Earth.

8

1 Evidence of the Past . . . . . . . . 194

2 Eras of the GeologicTime Scale. . . . . . . . . . . . . . . . . 200

3 Humans and OtherPrimates . . . . . . . . . . . . . . . . . . 206

START-UPMaking a FossilIn this activity, you will make a model of a fossil.

Procedure1. Get a paper plate, some modeling clay, and a

leaf or a shell from your teacher.

2. Flatten some of the modeling clay on the paper plate. Push the leaf or shell into the clay. Be sure that your leaf or shell has made a mark in the clay. Remove the leaf or shell carefully.

3. Ask your teacher to cover the clay with plaster of Paris. Allow the plaster to dry overnight.

4. Carefully remove the paper plate and the clay from the plaster the next day.

Analysis1. Consider the following objects—a clam, a seed, a

jellyfish, a crab, a leaf, and a mushroom. Which of the objects do you think would make good fossils? Explain your answers.

2. In nature, fossils form only under certain condi-tions. For example, fossils may form when a dead organism is covered by tiny bits of sand or dirt for a long period of time. The presence of oxygen can prevent fossils from forming. Considering these facts, what are some limitations of your model of how a fossil is formed?

Chapter 8 • The History of Life on Earth 193

START-UPSTART-UP vvM A T E R I A L S

FOR EACH STUDENT• clay, modeling• leaf or shell• plaster of Paris• plate, paper

Teacher’s Note: Coating the leaves or shells with a light veg-etable oil will help prevent the clay and plaster from sticking.

Answers

1. Sample answer: The crab, the clam, and perhaps the seed will make the best fossils because they have hard parts that would decay slowly and leave clear impressions. The softer objects—the jellyfish, the leaf, and the mushroom—are less likely to make impressions in the sediment and more likely to decay quickly, so they are less likely to form fossils.

2. Sample answer: Like all models, this model cannot encompass all real possibilities. This model does not exactly duplicate the way most fossils are formed. For example, this model does not show how fossils of softer organisms can be formed. Also, in this model, oxygen is present, but the plaster forms into rock quickly, so the objects are not given time to decay. Finally, in this model, the objects do not move on their own, but moving organisms might leave fossils of traces such as footprints.

The History of Life on Earth CHAPTER STARTER

One day you and your friends learnabout a secret underground passage thatleads into an old abandoned mansion,and you set out to find it. As you walkaround a field in search of the passage,you stumble across a large hole in theground. Could this be it?

One by one, you and your friendssqueeze down into the hole. You slidedown the sloping tunnel andfinally land. Dusting yourself off,you turn on your flashlight.Instead of finding a passage toan abandoned mansion, you andyour friends find yourselves in animmense cavern. Painted high onthe cavern’s walls are pictures ofbulls, cows, horses, and stags. Youget the feeling these images havebeen here for a very long time.Who made these paintings?

This adventure actually occurred insouthern France in the late 1940s. Fourteenage boys went hunting for a passage-way to the old manor of Lascaux. Insteadof finding a passageway, they stumbledonto a 17,000-year-old connection withour ancestors, the Cro-Magnons. Three ofthe adventurers are shown below talkingto their teacher.


Imagine . . .

Chapter Starter TransparencyUse this transparency to help students begin thinking about evidence of past life on Earth.

CHAPTER RESOURCESTechnology

Transparencies• Chapter Starter Transparency

Student Edition on CD-ROM

Guided Reading Audio CD• English or Spanish

Classroom Videos• Brain Food Video Quiz

Workbooks

Science Puzzlers, Twisters & Teasers• The History of Life on Earth g

READINGSKILLS

READING STRATEGY

Evidence of the PastIn 1995, scientist Paul Sereno found a dinosaur skull that was 1.5 m long in the Sahara, a desert in Africa. The dinosaur may have been the largest land predator that has ever existed!

Scientists such as Paul Sereno look for clues to help themreconstruct what happened in the past. These scientists, calledpaleontologists (PAY lee uhn TAHL uh jists), use fossils to recon-struct the history of life before humans existed. Fossils show usthat life on Earth has changed a great deal. They also provideus clues about how those changes happened.

FossilsFossilsFossils are traces or imprints of living things—such as animals,plants, bacteria, and fungi—that are preserved by geologicalprocesses. Fossils sometimes form when a dead organism iscovered by a layer of sediment. The sediment may later bepressed together to form sedimentary rock. Figure 1 shows oneway that fossils can form in sedimentary rock.

1

fossilfossil the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock

Fossils can form in several ways. The most common way is when an organism dies and becomes buried in sediment.

The organism gradually decomposes and leaves a hollow impression, or mold,in the sediment.

Over time, the mold fills with sediment, which forms a cast ofthe organism.

Figure 1 One Way Fossils Can Form

1

2

3

What You Will Learn

Explain how fossils can be formedand how their age can be estimated.Describe the geologic time scale andthe way that scientists use it.Compare two ways that conditionsfor life on Earth have changed overtime.

Vocabularyfossilrelative datingabsolute datinggeologic time scaleextinctplate tectonics

Reading Organizer As you readthis section, make a concept map byusing the terms above.

OverviewThis section introduces studentsto fossils and how they provideclues to Earth’s past. Studentslearn how fossils most com-monly form in sedimentaryrock. They explore the methodsscientists use to determine theage of fossils. They learn howscientists place events in theEarth’s history in the correctorder and how mass extinctionsmark the boundaries of eras.Finally, they learn how platetectonics has moved conti-nents slowly and affected lifeover time.

BellringerAsk students to imagine thatthey haven’t cleaned their roomfor 30 years. After 30 years, theyfinally decide to sort throughthe 2 m pile of stuff on theirfloor. Ask students, “What mightyou find on the top of the pile?in the middle? on the bottom?”(The items on the bottom are mostlikely to be those that were left onthe floor at an earlier time thanwere the items above them.)

oFossil Finds In the 1870s, two Americanscientists, Edward Drinker Cope andOthniel Charles Marsh, studied dinosaurfossils. They became bitter rivals and oftenargued. In 1878, Marsh and Cope wereboth excavating fossils in Wyoming. Theyhad separate excavations and didn’t wantto share their findings. Both groups foundmore fossils than they could carry. To pre-vent the other group from taking theirfossils, each group smashed all the fossilsthat couldn’t be carried away.

1

CHAPTER RESOURCES

Chapter Resource File

CRF • Lesson Plan • Directed Reading Ab • Directed Reading Bs

Technology

Transparencies• Bellringer• L27 Using Half-Lives to Date Fossils

Workbooks

Interactive Textbook Struggling Readers Struggling Readers


Am

ount

of

unst

able

ato

ms

(mg)

Time

1half-life

2half-lives

3half-lives

2

1

0.5

4

Rockforms

A

B

CD

The Age of FossilsSedimentary rock has many layers. The oldest layers are usu-ally on the bottom. The newest layers are usually on the top.The layers can tell a scientist the relative age of fossils. Fossilsfound in the bottom layers are usually older than the fossilsin the top layers. So, scientists can determine whether a fossilis older or younger than other fossils based on its position insedimentary rock. Estimating the age of rocks and fossils inthis way is called relative dating.

In addition, scientists can determine the age of a fossilmore precisely. Absolute dating is a method that measures theage of fossils or rocks in years. In one type of absolute dating,scientists examine atoms. Atoms are the particles that makeup all matter. Atoms, in turn, are made of smaller particles.Some atoms are unstable and will decay by releasing energy,particles, or both. When an atom decays it becomes a different,and more stable, kind of atom. Each kind of unstable atomdecays at its own rate. As shown in Figure 2, the time it takesfor half of the unstable atoms in a sample to decay is thehalf-life of that type of unstable atom. By measuring the ratioof unstable atoms to stable atoms, scientists can determine theapproximate age of a sample of rock.

✓Reading Check Which type of fossil dating is more precise?(See the Appendix for answers to Reading Checks.)

relative dating any method ofdetermining whether an event orobject is older or younger than otherevents or objects

absolute dating any method ofmeasuring the age of an object orevent in years

Using Half-Lives to Date FossilsFigure 2

Fractions of FractionsFind the answer to each ofthe following problems. Besure to show your work. Youmay want to draw pictures.1. 1/2 � 1/2 � 1/2 � 1/22. 1/2 � 1/83. 1/4 � 1/4

A The unstable atoms in this sampleof rock have a half-life of 1.3 billionyears. The sample contained 4 mgof unstable atoms when it formed.

After 1.3 billion years, (one half-life for this type of unstable atom),2 mg of the unstable atoms havedecayed to become stable atoms,and 2 mg of unstable atoms remain.

After 2.6 billion years (two half-livesfor this sample), the rock samplecontains 3 mg of stable decayatoms and 1 mg of unstable atoms.

After three half-lives, only 0.5 mg ofunstable atoms remain in the rocksample. This is equal to one-eighthof the original amount.

B

C

DAtoms of unstableelement

Atoms of stabledecay product

vv---------------------------------------------------g

Newspaper Layers Obtain astack of old daily newspapers.Tell students that the dailies rep-resent layers of sedimentary rockand that the pictures on thefront pages represent fossils.Scramble the newspapers tomake sure that they are notordered according to date. Then,have students stack the news-papers from oldest to newest tosimulate the layering of fossilsover time. l Kinesthetic

CONNECTION toCONNECTION toChemistry -----------------------------------------------a

Half-Lives The unstable atomsreferred to in Figure 2 areunstable because they have anunusual number of neutrons.Atoms of the same element canoccur as isotopes in which thenumber of neutrons per atomdiffers. For example, most car-bon atoms have 12 protons, 12neutrons, and 12 electrons. Butthe isotope carbon-14 has 14neutrons. Scientists have experi-mentally determined the half-lives of various isotopes in orderto determine the accuracy of ageestimates based on a givenisotope. l Logical

Answer to Reading Check

absolute dating

Answers to Math Practice

1. 1/162. 1/163. 1/16

SUPPORT FOR

English Language LearnersAbsolute and Relative Dating Studentsmay benefit from everyday examples ofabsolute and relative dating. Ask studentsto write down a schedule of what theydid last Monday, including specific timesas they best remember them. Then, ingroups of 3, have students answer eachother’s questions about when they did anactivity. For three minutes, have studentsanswer questions with specific times.When time is up, ask students if this was

an example of relative dating or absolutedating and why. Then, have students an-swer additional questions using words likebefore and after instead of specific times.Ask if this is relative or absolute dating.Discuss which method is more accurate,as well as why the other method mightbe useful even though it isn’t as accurate.l Verbal/Interpersonal

Section 1 • Evidence of the Past 195

The Geologic Time ScaleThink about important events that have happenedduring your lifetime. You usually recall each event interms of the day, month, or year in which it happened.These divisions of time make it easier to recall when youwere born, when you kicked the winning soccer goal,or when you started the fifth grade. Scientists also usea type of calendar to divide Earth’s long history. Thespan of time from the formation of Earth to now isvery long. Therefore, the calendar is divided into verylong units of time.

The calendar scientists use to outline the history oflife on Earth is called the geologic time scale,geologic time scale, shown inTable 1. After a fossil is dated, a paleontologist can placethe fossil in chronological order with other fossils. Thisordering forms a picture of the past that shows howorganisms have changed over time.

Divisions in the Geologic Time ScalePaleontologists have divided the geologic time scale intolarge blocks of time. Each block may be divided intosmaller blocks of time as scientists continue to findmore fossil information.

The divisions known as eras are characterized by thetype of organism that dominated Earth at the time. Forinstance, the Mesozoic era—dominated by dinosaurs andother reptiles—is referred to as the Age of Reptiles. Erasbegan with a change in the type of organism that wasmost dominant.

Paleontologists sometimes adjust and add details tothe geologic time scale. The early history of Earth hasbeen poorly understood because fossils from this periodare rare. So, the earliest part of the geologic time scaleis not named as an era. But more evidence of life beforethe Paleozoic era is being gathered. Scientists have pro-posed using this evidence to name new eras before thePaleozoic era.

Tertiary 65.5

Precambrian time

Era Period Time*

Table 1 Geologic Time Scale

Cenozoic era

Mesozoic era

Jurassic 200

Triassic 251Paleozoic era

Carboniferous 359

Devonian 416

Silurian 444

Ordovician 488

Cambrian 542

Quaternary 1.8

Cretaceous 146

Permian 299

4,600

*indicates how many millions of years ago theperiod began

A Place in Time Most of the periods of the Paleozoic erawere named by geologists for places where rocks from thatperiod are found. Research the name of each period of thePaleozoic era listed in Table 1. On a copy of a world map,label the locations related to each name.

GroupGroup vv -------a

Detailed Geologic TimelineTable 1 shows that geologictime is divided into eras, whichare broken into smaller divisionscalled periods. But periods canbe divided into epochs, and sci-entists continue to add manymore details to this table.Challenge students to constructa giant geologic timeline thatidentifies all of these divisions.Direct them to scale the size ofthe divisions relative to time.Allow them to do research inthe library or on the Internetfor information. l Visual

Research -------------------------------------------g

Extinct Species Students couldresearch plant and animal spe-cies that have become extinctwithin the last 200 years. Manyof the extinctions were causedby human activities. Extinctbirds include the dodo, greatauk, Labrador duck, moa, andpassenger pigeon. Extinct mam-mals include the Steller’s seacow and the quagga. l Verbal

Discussion ----------------------------------g

Abbreviations In geologicaland paleontological literature,students may encounter theabbreviations MYA and BYA.Explain to students that MYAmeans “million years ago.”Likewise, BYA means “billionyears ago.” Ask students whythey think geologists use thisform of dating. l Verbal Answer to Connection

to Social Studies

Cambrian: for Cambria, the Latin name for Walesin Great Britain; Ordovician: after the Ordivices,a Celtic tribe; Silurian: after the Silures, a Celtictribe; Devonian: for Devonshire, England;Carboniferous: for coal-bearing rocks in England;Permian: for the Russian province of Perm

Private Fossil Collectors In 1997, themost complete skeleton ever found of aTyrannosaurus rex was auctioned. Thewinning bid was $8.36 million, made bythe Field Museum of Natural History inChicago. Scientists were relieved that amuseum won the bid; their fear was thata private collector would buy the skeletonfossil and not allow scientists to study it.


Mass ExtinctionsSome of the important divisions in the geologic time scalemark times when rapid changes happened on Earth. Duringthese times, many species died out completely, or becameextinct. When a species is extinct, it does not reappear. Atcertain points in the Earth’s history, a large number of speciesdisappeared from the fossil record. These periods when manyspecies suddenly become extinct are called mass extinctions.

Scientists are not sure what caused each of the mass extinc-tions. Most scientists think that the extinction of the dinosaurshappened because of extreme changes in the climate on Earth.These changes could have resulted from a giant meteorite hit-ting the Earth, as shown in Figure 3. Or, forces within the Earthcould have caused many volcanoes and earthquakes.

✓Reading Check What are mass extinctions?

geologic time scale the standardmethod used to divide the Earth’slong natural history into manageableparts

extinct describes a species that hasdied out completely

Figure 3 Scien-tists think that ameteorite hit Earthabout 65 millionyears ago andcaused majorclimate changes.

Making a Geologic Timeline

1. Use a metric ruler to mark 10 cm sections on astrip of paper that is 46 cm long.

2. Label each 10 cm section in order from top tobottom as follows: 1 bya (billion years ago),2 bya, etc. The timeline begins at 4.6 bya.

3. Divide each 10 cm section into 10 equal sub-sections. Divide the top 1 cm into 10 subsec-tions. Calculate the number of years that arerepresented by 1 mm on this scale.

4. On your timeline, label the following events:a. Earth forms. (4.6 billion years ago)b. First animals appear. (600 million years ago)c. Dinosaurs appear. (251 million years ago)d. Dinosaurs are extinct. (65 million years ago)e. Humans appear. (160,000 years ago)

5. Label other events from the chapter.6. Describe what most of the timeline looks like.7. Compare the length of time dinosaurs existed

with the length of time humans have existed.

vv ------------------------------------------gRock Collectors If any stu-dents have rock collections, askthem to show these collectionsto the class. Allow studentstime to observe the differentcollections and to ask questionsabout them.l Interpersonal ee


periods of sudden extinction ofmany species

M A T E R I A L SFOR EACH GROUP

• paper, adding machine, 46 cm strip• ruler, metric

Teacher’s Note: A fun varia-tion on this activity uses afull roll of perforated toiletpaper instead of adding-machine paper. At the scaleof 20 million years per perfo-rated sheet, 4.6 billion yearswould be represented by 230sheets. This activity variationwould best be conducted out-doors or in a long hallway.

Answers

6. Most of the timeline should beblank and should be taken upby Precambrian time.

7. Dinosaurs existed for a muchlonger time than humans have.

h-----------------------------g

PORTFOLIO

Poster Project Havestudents research what

their local area was like millionsof years ago. They can develop awritten report and a posterdescribing the climate, livingthings, and landforms at differ-ent points in time. l Visual

CHAPTER RESOURCES


• Datasheet for Quick Labg

Workbooks

Math Skills for Science• Geologic Time Scaleg• Radioactive Decay and the Half-Lifeg

Technology

Transparencies• L117 The Geologic Time Scale

One species that became extinct duringthe time of the dinosaurs was the insecthaving the largest wingspan on record.The insect belonged to the orderProtodonata, and it measured an aston-ishing 76 cm (30 in.) from wingtip towingtip. Its body was 46 cm (18 in.)long. It died out about 200 million yearsago. Fossils of this insect have beenfound in Kansas.

CRF


PANTHALASSAOCEAN

NorthAmerica

SouthAmerica

Eurasia

Africa

India

Antarctica

Australia

PA

NG

AE

A

PA

N G A E A

SouthAmericanplate

Africanplate

The Changing EarthDid you know that fossils of tropical plants have been found in Antarctica? Antarctica, now frozen, must have once had a warm climate to support these plants. The fossils provide evi-dence that Antarctica was once located near the equator!

PangaeaHave you ever noticed that the continents look like pieces of a puzzle? German scientist Alfred Wegener had a simi lar thought in the early 1900s. He proposed that long ago the continents formed one landmass surrounded by a gigantic ocean. Wegener called that single landmass Pangaea (pan JEE uh), which means “all Earth.” Figure 4 shows how the continents may have formed from Pangaea.

✓Reading Check What idea did Alfred Wegener propose?

Do the Continents Move?In the mid-1960s, J. Tuzo Wilson of Canada came up with the idea that the continents were not moving by themselves. Wil-son thought that huge pieces of the Earth’s crust were pushed around by forces within the planet. Each huge piece of crust is called a tectonic plate. Wilson’s theory of how these huge pieces of crust move around the Earth is called plate tectonics.

According to Wilson, the outer crust of the Earth is broken into seven large, rigid plates and several smaller ones. The continents and oceans ride on top of these plates. The motion of the plates causes the continents to move. For example, the plates that carry South America and Africa are slowly moving apart, as shown in Figure 5.

Figure 4 The continents have been slowly moving throughout the history of Earth. The colored areas show the location of the continents 245 million years ago, and blue outlines show where the continents are today.

plate tectonics the theory that explains how large pieces of the Earth’s outermost layer, called tectonic plates, moveand change shape

Figure 5 The continents ride on tectonic plates, outlined here in black. The plates are still moving about 1 to 10 cm per year.


Reteaching -------------------------------------bIllustrating Drift Have students cut out each continent from a copy of an area-proportionate world map. Have them try to fit the cut-out continents together into one landmass, using Figure 4 as a model. Then, ask students to model the movements of the conti-nents into their current loca-tions. Finally, ask them to predict where the continents might be in the future if they keep moving in a similar way. (Predictions might include a wider Atlantic Ocean and a shift north-ward of Africa, Australia, and South America.) l Visual/Kinesthetic

Quiz ---------------------------------------------------------------------g

1.How are fossils most com-monly formed? (An organism is buried in sediments that harden into rock.)

2.What can scientists learn about Earth’s past from fossils? (how life on Earth has changed over time)

3.Why would fossils found at the top of a canyon probably be younger than those found at the bottom of the canyon? (The upper layers were deposited more recently.)


the idea that the Earth’s continents once formed a single landmass sur-rounded by oceans

CulturalAwarenessCulturalAwareness g

Iceland Tell the class that the Mid-Atlantic Ridge rises above water only in Iceland. Point to Iceland (in the Arctic Circle) on a map. Tell students that Iceland is a place of both extreme cold and extreme heat. Ask students to do some research on what life is like in Iceland. Have them focus on how geo-logic processes, such as glaciers, geysers, and volcanic activity, affect the lifestyle of the people who live there. l Visual

StrategiesStrategiesINCLUSIONINCLUSION

• Visually Impaired • Learning Disabled• Developmentally DelayedAssist students in understanding the concepts in Figure 4 by creating a card-board replica of each of the continents. Let students experiment with fitting the pieces together. Then, have them approximate the shape of Pangaea, as shown in Figure 4.l Kinesthetic ee


For a variety of links related to thischapter, go to www.scilinks.org

SummarySummary

Review

Adaptation to Slow ChangesWhen conditions on the Earth change, organisms may becomeextinct. A rapid change, such as a meteorite impact, may causea mass extinction. But slow changes, such as moving conti-nents, allow time for adaptation.

Anywhere on Earth, you are able to see living things thatare well adapted to the location where they live. Yet in thesame location, you may find evidence of organisms that livedthere in the past that were very different. For example, theanimals currently living in Antarctica are able to survive verycold temperatures. But under the frozen surface of Antarcticaare the remains of tropical forests. Conditions on Earth havechanged many times in history, and life has changed, too.

• Fossils are formed mostoften in sedimentaryrock. The age of a fossilcan be determined usingrelative dating and abso-lute dating.

• The geologic time scaleis a timeline that is usedby scientists to outlinethe history of Earth andlife on Earth.

• Conditions for life onEarth have changedmany times. Rapidchanges, such as ameteorite impact, mighthave caused massextinctions. But manygroups of organismshave adapted to changessuch as the movementof tectonic plates.

Using Key Terms

1. Use the following terms in thesame sentence: fossil and extinct.

2. In your own words, write adefinition for the term platetectonics.

Understanding Key Ideas

3. Explain how a fossil forms insedimentary rock.

4. What kind of information doesthe geologic time scale show?

5. About how many years ofEarth’s history was Precambriantime?

6. What are two possible causes ofmass extinctions?

Math Skills

7. The Earth formed 4.6 billionyears ago. Modern humans haveexisted for about 160,000 years.Simple worms have existed forat least 500 million years. Forwhat fraction of the history ofEarth have humans existed?have worms existed?

Critical Thinking

8. Identifying Relationships Whyare both absolute dating andrelative dating used to determinethe age of fossils?

9. Making Inferences Fossils ofMesosaurus, the small aquaticreptile shown below, have beenfound only in Africa and SouthAmerica. Using what you knowabout plate tec tonics, howwould you explain this finding?

Topic: Evidence of the PastSciLinks code: HSM0545

Mid-Atlantic Ridge In 1947,scientists examined rock froma ridge that runs down themiddle of the Atlantic Ocean,between Africa and the Ameri-cas. They found that this rockwas much younger than therock on the continents. Explainwhat this finding indicatesabout the tectonic plates.

AlternativeAssessment ---------------------------g

Geologic Time Scale Each stu-dent in a group receives threeblank cards. The group looks atTable 1 in this section andthinks of questions that couldbe answered using informationfrom the table. Students write aquestion on one side of a card.They stack the cards with theblank sides up. In turn, each stu-dent draws a card, reads thequestion on it, and attempts toanswer the question. Groupmembers determine if theanswer is correct by consultingthe table. l Visual/Interpersonal

Answer to Connectionto Geology

This finding indicates that the platesare spreading apart as newer rockforms at the center.

Answers to Section Review

1. Sample answer: Scientists canlearn about extinct organismsfrom fossils.

2. Sample answer: Plate tectonicsis a theory about how the platesof the Earth’s crust move around.

3. A fossil may form when a deadorganism is covered by a layer ofsediment. Then, these sedimentsare slowly pressed together toform sedimentary rock.

4. how organisms and Earth havechanged over time

5. about 4 billion years6. meteorite impacts and forces

within the Earth7. Humans have existed for

16/460,000 of the history of Earth.Worms have existed for 5/46 ofEarth’s history.

8. Sample answer: to compare theresults of each method so therecan be greater confindence inthe conclusions

9. Sample answer: PerhapsMesosaurus evolved afterPangaea broke up but beforeSouth America and Africa splitapart.

CONNECTION toCONNECTION toEarth Science ---------------------------g

The South American Plate Have studentsidentify the boundaries of the SouthAmerican tectonic plate on a map. Ask stu-dents, “What kinds of features mark theeast side of the plate?” (a rift or canyon downthe middle of the Atlantic Ocean) Ask, “Whichdirection is the plate drifting?” (to the west,away from Africa.) Ask, “What is happeningon the west side of the plate?” (the plate iscrashing into another plate and pushing upthe Andes moutnains) l Visual

CHAPTER RESOURCES


CRF • Section Quizg • Section Reviewg • Vocabulary and Section Summaryg • Reinforcement Worksheetb • Datasheet for Quick Lab

Technology

Transparencies• L29 Moving Continents and Tectonic Plates


READING STRATEGY

Precambrian timePrecambrian time the period in the geologic time scale from the formation of the Earth to the begin-ning of the Paleozoic era, from about 4.6 billion to 542 million years ago

Figure 1 This illustration shows the conditions under which the first life on Earth may have formed.

2Eras of the Geologic Time ScaleThe walls of the Grand Canyon are layered with different kinds and colors of rocks. The deeper down into the canyon you go, the older the layers of rocks. Try to imagine a time when the bottom layer was the only layer that existed.

Each layer of rock tells a story about what was happening onEarth when that layer was on top. The rocks and fossils ineach layer tell the story. Scientists have compared the storiestold by fossils and rocks all over the Earth. From these stories,scientists have divided geologic history into four major parts.These divisions are Precambrian time, the Paleozoic era, theMesozoic era, and the Cenozoic era.

Precambrian TimeThe layers at the bottom of the Grand Canyon are fromthe oldest part of the geologic time scale. Precambrian timePrecambrian time(pree KAM bree UHN TIEM) is the time from the formation ofEarth 4.6 billion years ago to about 542 million years ago. Lifeon Earth began during this time.

Scientists think that the early Earth was very different thanit is today. The atmosphere was made of gases such as watervapor, carbon dioxide, and nitrogen. Also, the early Earth wasa place of great turmoil, as illustrated in Figure 1. Volcaniceruptions, meteorite impacts, and violent storms were common.Intense radiation from the sun bombarded Earth’s surface.

✓✓Reading Check Describe the early Earth. (See the Appendix for answers to Reading Checks.)

What You Will Learn

Outline the major developments thatallowed life to exist on Earth.Describe the types of organisms thatarose during the four major divisionsof the geologic time scale.

VocabularyPrecambrian timePaleozoic eraMesozoic eraCenozoic era

Mnemonics As you read this section,create a mnemonic device to helpyou remember the eras of geologictime.

OverviewThis section discusses currenttheories regarding the originof life. Students are introducedto the four major divisions ofgeologic time in chronologicalorder: Precambrian time, thePaleozoic era, the Mesozoic era,and the Cenozoic era. Theylearn about the organisms thatcharacterize each era.

BellringerAsk students to respond to thefollowing question:

Suppose that electrical energyhad never been developed.How would your life differfrom what it is like now?

Discuss with students the conse-quences of great changes overtime.


The early Earth was very differentfrom Earth as it is today. Therewere violent events and a harshatmosphere.

2

CHAPTER RESOURCES


CRF • Lesson Plan• Directed Reading Ab• Directed Reading Bs

Technology

Transparencies• Bellringer

Workbooks


Is That a Fact!Throughout Earth’s history, the forces oferosion have been altering the planet’ssurface, making it almost impossible tofind rocks older than 3.5 billion years.However, a number of rocks dating fromabout 3.5 billion to 3.9 billion yearsago have been found in Canada andGreenland. The oldest was found in theNorthwest Territories of Canada in 1989.


How Did Life Begin?Scientists think that life developed from simple chemicals inthe oceans and in the atmosphere. Energy from radiation andstorms could have caused these chemicals to react. Some ofthese reactions formed the complex molecules that made lifepossible. Eventually, these molecules may have joined to formstructures such as cells.

The early atmosphere of the Earth did not contain oxygengas. The first organisms did not need oxygen to survive. Theseorganisms were prokaryotes (proh KAR ee OHTS), or single-celledorganisms that lack a nucleus.

Photosynthesis and OxygenThere is evidence that cyanobacteria, a new kind of prokaryoticorganism, appeared more than 3 billion years ago. Some cyano-bacteria are shown in Figure 2. Cyanobacteria use sunlight toproduce their own food. Along with doing other things, thisprocess releases oxygen. The first cyanobacteria began to releaseoxygen gas into the oceans and air.

Eventually, some of the oxygen formed a new layer of gasin the upper atmosphere. This gas, called ozone, absorbs harm-ful radiation from the sun, as shown in Figure 3. Before ozoneformed, life existed only in the oceans and underground. Thenew ozone layer reduced the radiation on Earth’s surface.

Multicellular OrganismsAfter about 1 billion years, organisms that were larger andmore complex than prokaryotes appeared in the fossil record.These organisms, known as eukaryotes (yoo KAR ee OHTS),contain a nucleus and other complex structures in their cells.Eventually, eukaryotic cells may have evolved into organismsthat are composed of many cells.

Figure 2 Cyanobacteria are thesimplest living organisms thatuse the sun’s energy to producetheir own food.

Figure 3 Oxygen in theatmosphere formed a layer ofozone, which helps to absorbharmful radiation from the sun.

Ozone

Atmosphere

Radiation

For another activity relatedto this chapter, go togo.hrw.com and type in thekeyword HL5HISW.

Discussion ----------------------------------gHistorical Perspective Havestudents pretend that they arein a time-travel machine. Whatscientifically significant eventswould they witness as theytravel back in time to Earth’s ori-gin? List the events on the boardin the order that they are sug-gested. Ask students how theycan determine whether theevents are in chronologicalorder. (Students can consult thegeologic time scale or other scien-tific materials.) l Verbal/Logical

vv --------------------------------------------------g

Using Maps Have studentslocate the following three earth-quake and volcano zones on aworld map. One zone extendsnearly all the way around theedge of the Pacific Ocean. A sec-ond zone is located near theMediterranean Sea and extendsacross Asia into India. The thirdzone extends through Iceland tothe middle of the AtlanticOcean. l Visual

CONNECTIONCONNECTION vvEarth Science ----------------------------g

Ancient Mountains Provide a large wallmap of the world, and provide map pins ortacks in three colors. Have students locatethe following mountain ranges on a map.Have students place pins on the map foreach range to match the eras when eachrange was formed. Use the following listfor reference:

Blue (Paleozoic):• Caledonian (Scandinavia), Acadian (New

York), Appalachian (eastern NorthAmerica), Ural (Russia)

Green (Mesozoic):• Palisades (New Jersey), Rockies (western

North America)

Red (Cenozoic):• Andes (South America), Alps (Europe),

Himalayas (Asia)l Visual/Kinesthetic

SUPPORT FOR

English LanguageLearnersTimeline Mural Students willbetter understand the divisionof time if they can see the dif-ferences between the periodsor eras covered in this section.Give groups of 4 students afour-foot piece of butcherpaper, marked off in one-footsections. Each group membershould re-create one of thetime periods in its correct posi-tion on the mural. Each periodshould include the nameand time span of the period,descriptions of the world atthat time, and labeled draw-ings of plant and animal life asappropriate.l Visual/Verbal

Section 2 • Eras of the Geologic Time Scale 201

The Paleozoic EraThe Paleozoic eraPaleozoic era (PAY lee OH ZOH ik ER uh) beganabout 542 million years ago and ended about 251million years ago. Considering the length of Pre-cambrian time, you can see that the Paleozoic erawas relatively recent. Rocks from the Paleozoic eraare rich in fossils of animals such as sponges, corals,snails, clams, squids, and trilobites. Fishes, the earli-est animals with backbones, appeared during thisera, and sharks became abundant. Figure 4 showsan artist’s depiction of life in the Paleozoic era.

The word Paleozoic comes from Greek words thatmean “ancient life.” When scientists first namedthis era, they thought it held the earliest forms oflife. Scientists now think that earlier forms of lifeexisted, but less is known about those life-forms.Before the Paleozoic era, most organisms lived inthe oceans and left few fossils.

Life on LandDuring the 300 million years of the Paleozoic era,plants, fungi, and air-breathing animals slowly colo-nized land. By the end of the era, forests of giantferns, club mosses, horsetails, and conifers coveredmuch of the Earth. All major plant groups exceptfor flowering plants appeared during this era. Theseplants provided food and shelter for animals.

Fossils indicate that crawling insects were someof the first animals to live on land. They were fol-lowed by large salamander-like animals. Near theend of the Paleozoic era, reptiles and winged insectsappeared.

The largest mass extinction known took place at the end ofthe Paleozoic era. By 251 million years ago, as many as 90% ofmarine species had become extinct. The mass extinction wipedout entire groups of marine organisms, such as trilobites. Theoceans were completely changed.

Paleozoic eraPaleozoic era the geologic era thatfollowed Precambrian time and thatlasted from 542 million to 251 mil-lion years ago

Figure 4 Organisms that firstappeared in the Paleozoic erainclude reptiles, amphibians,fishes, worms, and ferns.

Prehistoric Marine Organisms Find a variety of pictures anddescriptions of marine organisms from the Cambrian period of thePaleozoic era. Choose three organisms that you find interesting.Draw or write a description of each organism. Find out whetherscientists think the organism is related to any living group of organ-isms, and add this information to your description.

GroupGroup vv -------g

Ancient Plants Organize theclass into five groups, and assigneach group one of the followinggroups of paleozoic plants: clubmosses, ferns, horsetails, ginkos,or conifers.

Have each group use encyclo-pedias or botany books to lookup the plant group and preparea poster about it. Have studentsinclude diagrams of key featuresof the plant group and picturesof fossils and living examples ofthe group. l Interpersonal/Visualcc

CONNECTIONCONNECTION vvReal World ------------------------------------g

Fossil Fuels The huge plantsthat grew in forests during thePaleozoic era later became coal.Ask students to research thelocations of the world’s coaldeposits and to mark them ona world map. (Most of the knowncoal reserves are in Australia,China, Germany, Poland, GreatBritain, India, Russia, South Africa,the United States, and Canada.)l Visual

Answer to Connectionto Oceanography

Descriptions may vary.

all students can see it. Then, choose adifferent team’s model, and place it ontop of the first, squashing the bottomorganisms. Continue in this manneruntil all circles have been stacked. Slicea cross section through the stack for allto see.l Kinesthetic ee

StrategiesStrategiesINCLUSIONINCLUSION

• Hearing Impaired • Learning Disabled• Visually ImpairedDemonstrate the superposition of geo-logic layers. Have student teams each usea different color of modeling clay to cre-ate a 3 in diameter circle, representing apiece of land. Ask teams to use otherpieces of clay to add organisms to theland. Choose one team’s model to repre-sent early organisms, and place it where


Figure 5 The Mesozoic era was dominated by dinosaurs. The era ended with the mass extinction of many species.

Mesozoic eraMesozoic era the geologic era that lasted from 251 million to 65.5 million years ago; also called the Age of Reptiles

The Mesozoic EraThe Mesozoic eraMesozoic era (MES oh ZOH ik ER uh) beganabout 251 million years ago and lasted about 185.5million years. Mesozoic comes from Greek wordsthat mean “middle life.” Scientists think that thesurviving reptiles evolved into many different spe-cies after the Paleozoic era. Therefore, the Mesozoicera is commonly called the Age of Reptiles.

Life in the Mesozoic EraDinosaurs are the most well known reptiles thatevolved during the Mesozoic era. Dinosaurs domi-nated the Earth for about 150 million years. Agreat variety of dinosaurs lived on Earth. Somehad unique adaptations, such as ducklike bills forfeeding or large spines on their bodies for defense.In addition to dinosaurs roaming the land, giantmarine lizards swam in the ocean. The first birdsalso appeared during the Mesozoic era. In fact, sci-entists think that some of the dinosaurs becamethe ancestors of birds.

The most important plants during the early partof the Mesozoic era were conifers, which formedlarge forests. Flowering plants appeared later inthe Mesozoic era. Some of the organisms of theMesozoic era are illustrated in Figure 5.

The Extinction of DinosaursAt the end of the Mesozoic era, 65.5 millionyears ago, dinosaurs and many other animal andplant species became extinct. What happenedto the dinosaurs? According to one hypothesis,a large meteorite hit the Earth and generatedgiant dust clouds and enough heat to causeworldwide fires. The dust and smoke from thesefires blocked out much of the sunlight andcaused many plants to die out. Without enoughplants to eat, the plant-eating dinosaurs diedout. And the meat-eating dinosaurs that fed on the plant-eating dinosaurs died. Global temperatures may havedropped for many years. However, some mammals and birdssurvived.

✓✓Reading Check What kind of event happened at the end of both the Paleozoic and Mesozoic eras?

READINGSTRATEGY -----------------g

Prediction Guide Before stu-dents read the text on this pageand the next, ask them to guesswhether the following eventsoccurred in the Mesozoic era orin the Cenozoic era:

• Dinosaurs dominated Earthand then died out by the endof this era. (Mesozoic)

• Mammals appeared. (Mesozoic)

• Rock layers close to Earth’s sur-face contain fossils from thisera. (Cenozoic)

• The first birds appeared.(Mesozoic)

• Humans appeared. (Cenozoic)l Logical/Auditory

Research -------------------------------------------g

Reptile Research Have stu-dents research reptiles and listtheir distinctive characteristics.(Reptiles are ectothermic, or “cold-blooded,” they all have a distinctivethree-chambered heart and at leastone lung, most reptiles have scalesbut not feathers or fur, many reptileshave claws, all reptiles produceamniotic eggs, and most lay theseeggs on land.) Tell students thatall living reptiles fall into fourmain groups—turtles, lizardsand snakes, crocodiles andrelated forms, and the tuatara.Have students investigate theseorders and list examples of each.l Verbal/Logical

Making Models ----------g

Dinosaur Models Dinosaursvaried greatly in size andappearance. Have groups ofstudents consult reference booksto find information about themany kinds of dinosaurs. Then,have them use art materials tomake models of different dino-saurs. Models should includeflying and marine reptilesas well as land-dwellingreptiles.l Kinesthetic ee


a mass extinctionCulturalAwarenessCulturalAwareness g

Dinosaur Food Recently, a fossilplesiosaur was found in a riverside cliffin Hokkaido, Japan, with shellfishremains in its stomach. Scientists hadlong suspected that plesiosaurs werepredators, but they had no proof.Geologist Tamaki Sato thinks that theplesiosaur swallowed its tiny prey wholebecause the plesiosaur’s long, sharpteeth were unsuitable for crushing hardouter shells.


x

543,000,000 years

1 h

383,000,000 years�

x �543,000,000 years � 1 h

383,000,000 years� 1.42 h

Figure 6 Many types of mammals evolved during the Cenozoic era.

Relative Scale It’s hard to imagine 4.6 billion years. One way is to use a relative scale. For example, we can represent all of Earth’s history by using the 12 h shown on a clock. The scale would begin at noon, representing 4.6 billion years ago, and end at midnight, representing the present. Because 12 h represent 4.6 billion years, 1 h represents about 383 million years. (Hint: 4.6 billion � 12 � 383 million) So, what time on the clock represents the beginning of the Paleozoic era, 543 million years ago?

Step 1: Write the ratio.

Step 2: Solve for x.

Step 3: Convert the answer to the clock scale.

1.42 h � 1 h � (0.42 � 60 min/h)

1.42 h � 1 h 25 min

So, the Paleozoic era began 1 h 25 min before midnight, at about 10:35.

Now It’s Your Turn1. Use this method to calculate

the relative times at which the Mesozoic and Cenozoic eras began.

The Cenozoic EraThe Cenozoic era (SEN uh ZOH ik ER uh) began about 65 million years ago and continues today. Cenozoiccomes from Greek words that mean “recent life.” Scientists have more information about the Ceno-zoic era than about any of the previous eras. Fossils from the Cenozoic era formed recently in geologic time, so they are found in rock layers closer to the Earth’s surface. The closer the fossils are to the surface, the easier they are to find.

During the Cenozoic era, many kinds of mam-mals, birds, insects, and flowering plants appeared. Some organisms that appeared in the Cenozoic era are shown in Figure 6.

✓Reading Check What does Cenozoic mean?

The Age of MammalsThe Cenozoic era is sometimes called the Age of Mammals. Mammals have dominated the Ceno-zoic era the way reptiles dominated the Mesozoic era. Early Cenozoic mammals were small, forest dwellers. Larger mammals appeared later in the era. Some of these larger mammals had long legs for run-ning, teeth that were specialized for eating different kinds of food, and large brains. Cenozoic mam-mals have included mastodons, saber-toothed cats, camels, giant ground sloths, and small horses.


Reteaching -------------------------------------bComparing Organisms Have students compare the character-istics of each of the Paleozoic, Mesozoic, and Cenozoic organ-isms described in this section with those of a living descen-dant (if one exists) of each of the organisms. Students can organize the information in the form of a chart. l Visual

Quiz ---------------------------------------------------------------------g

On index cards, write the names of several types of organisms that appeared in each the four major divisions of geologic time mentioned in this section. Then, on paper strips, write the names of the geologic time divisions, and place the strips on a table-top. Direct students to classify each organism named on a card by placing the card under the appropriate paper strip.

Alternative Assessment ---------------------------g

Diorama Organize students into groups of three or four. Groups should use boxes with covers and art materials to make a diorama of one of the four major divisions of geologic time mentioned in this section. l Interpersonal/Kinesthetic


“recent life”

Answer to Math Focus

Mesozoic:12 h � [(348 � 383) � 60] min � 11:21

Cenozoic:12 h � [(65 � 383) � 60] min � 11:50

CONNECTION toCONNECTION toMath -----------------------------------------------------------a

Another Time Scale Have students calcu-late the length of the major divisions of geologic time relative to a 365-day calen-dar. They should state the month and day that each of the eras began. Use the Math Focus as an example, and provide a calen-dar for reference. Also, have students calcu-late the day that humans appeared (about 150,000 years ago). (Precambrian: Jan. 1; Paleozoic: Nov. 16; Mesozoic: Dec. 12; Cenozoic: Dec. 26; humans appeared: Dec. 31) l Logical


For a variety of links related to thischapter, go to www.scilinks.org

SummarySummary

Review

The Cenozoic Era TodayWe are currently living in the Cenozoic era. Modern humansappeared during this era. The environment and landscapes thatwe see around us today are part of this era.

However, the climate has changed many times during theCenozoic era. Earth’s history includes some periods called iceages, during which the climate was very cold. During the iceages, ice sheets and glaciers extended from the Earth’s poles. Tosurvive, many organisms migrated toward the equator. Otherorganisms adapted to the cold or became extinct.

When will the Cenozoic era end? No one knows. In thefuture, geologists might draw the line at a time when life onEarth again undergoes major changes.

• The Earth is about 4.6billion years old. Lifeformed from nonlivingmatter long ago.

• Precambrian timeincludes the formationof the Earth and theappearance of simpleorganisms.

• The first cells did notneed oxygen. Later, pho-tosynthetic cells evolvedand released oxygen intothe atmosphere.

• During the Paleozoic era,animals appeared in theoceans and on land, andplants grew on land.

• Dinosaurs dominated theEarth during the Meso-zoic era.

• Mammals have domi-nated the Cenozoic era.This era continues today.

Using Key Terms

1. Use each of the following termsin a separate sentence: Precam-brian time, Paleozoic era, Mesozoicera, and Cenozoic era.


2. Unlike the atmosphere today,the atmosphere 3.5 billion yearsago did not contain

a. carbon dioxide.b. nitrogen.c. gases.d. ozone.

3. How do prokaryotic cells andeukaryotic cells differ?

4. Explain why cyanobacteria wereimportant to the developmentof life on Earth.

5. Place in chronological order thefollowing events on Earth:

a. The first cells appeared thatcould make their own foodfrom sunlight.

b. The ozone layer formed.c. Simple chemicals reacted to

form the molecules of life.d. Animals appeared.e. The first organisms appeared.f. Humans appeared.g. The Earth formed.

Math Skills

6. Calculate the total number ofyears that each of the geologiceras lasted, rounding to thenearest 100 million. Then, calcu-late each of these values as a per-centage of the total 4.6 billionyears of Earth’s history. Roundyour answer to the units place.

Critical Thinking

7. Making Inferences Whichchemicals probably made up thefirst cells on Earth?

8. Forming Hypotheses Think ofyour own hypothesis to explainthe disappearance of the dino-saurs. Explain your hypothesis.

Topic: Geologic Time ScaleSciLinks code: HSM0669

Cenozoic era the most recent geo-logic era, beginning 65 million yearsago; also called the Age of Mammals


1. Sample answer: Most ofEarth’s history wasPrecambrian time. ThePaleozoic era was the timewhen life began to colonizeland. The Mesozoic era isknown as the Age of Reptiles.The Cenozoic era is known asthe Age of Mammals.

2. d3. Eukaryotes have a nucleus

and are usually larger and morecomplex than prokaryotes.

4. Cyanobacteria were thefirst significant source of atmos-pheric oxygen on the planet.

5. g, c, e, a, b, d, f6. Precambrian time: 4,057

million years, 88%; Paleozoicera: 291 million years, 6%;Mesozoic era: 185.5 millionyears, 4%; Cenozoic era: 65.5million years, 1%

7. Sample answer: carbondioxide, water, and nitrogen (orcarbon, hydrogen, oxygen, andnitrogen)

8. Sample answers: A devas-tating virus attacked all reptileson Earth, and only a few sur-vived; a new kind of organism,such as a mammal, began tooutcompete the dinosaurs;aliens bombed the Earth withclimate-changing gases.

oFire or Ice Scientists continue to debatewhether another ice age is coming soon orwhether the Earth is overheating. DuringEarth’s history, the climate has changedmany times, slowly switching between icycold and lush warmth. Scientists call thewarmer periods interglacial because eachis usually followed by another ice age.However, in recent decades average tem-peratures on Earth seem to keep gettingwarmer.

CHAPTER RESOURCES


CRF • Section Quizg• Section Reviewg• Vocaulary and Section Summaryg• Reinforcement Worksheetb• SciLinks Activityg

Technology

Interactive Explorations CD-ROM• Rock On!g

Workbooks

Math Skills for Science• Subtraction Reviewb


READING STRATEGY

Humans and Other PrimatesHave you ever heard someone say that humans descended from monkeys or apes? Well, scientists would not exactly say that. The scientifi c theory is that humans, apes, and monkeys share a common ancestor. This common ancestor probably lived more than 45 million years ago.

Most scientists agree that there is enough evidence to supportthis theory. Many fossils of organisms have been found thatshow traits of both humans and apes. Also, comparisons ofmodern humans and apes support this theory.

PrimatesWhat characteristics make us human? Humans are classifiedas primates. PrimatesPrimates are a group of mammals that includeshumans, apes, monkeys, and lemurs. Primates have the char-acteristics illustrated in Figure 1.

The First PrimatesThe ancestors of primates may have co-existed with the dino-saurs. These ancestors were probably mouselike mammals thatwere active at night, lived in trees, and ate insects. The firstprimates did not exist until after the dinosaurs died out. About45 million years ago, primates that had larger brains appeared.These were the first primates that had traits similar to mon-keys, apes, and humans.

3

primateprimate a type of mammal char-acterized by opposable thumbs and binocular vision

Almost all primates, such as these orangutans, have five flexible fingers—four fingersand an opposable thumb. This thumb enables primates to grip objects. Most pri-mates besides humans also have opposable big toes.

Both eyes are located at the front of the head, and they provide binocular, or three-dimensional, vision.

Characteristics of PrimatesFigure 1

What You Will Learn

Describe two characteristics that allprimates share.

Describe three major groups ofhominids.

VocabularyprimatehominidHomo sapiens

Discussion Read this section silently.Write down questions that you haveabout this section. Discuss yourquestions in a small group.

OverviewIn this section, students willlearn that scientists thinkhumans share a common ances-tor and common characteristicswith other primates, such asapes and monkeys. This sectiondescribes the characteristics ofhominids and examines trendsin their evolution that couldhave led to modern humans.

BellringerAsk students to write an answerto the following question:

What makes you uniqueamong your family members?(Responses might include foodpreferences, health condition,physical appearance, and talents.)

Point out that understandinghuman ancestry requires recog-nizing similarities and differ-ences, such as those seen infamilies.

3

CHAPTER RESOURCES


CRF • Lesson Plan • Directed Reading Ab • Directed Reading Bs

Technology

Transparencies• Bellringer• L30 Comparison of Primate Skeletons

Workbooks


Is That a Fact!Although the skulls of a human and achimpanzee appear similar, there aresignificant differences. The cranium ofa human skull is domed, whereas thechimpanzee’s cranium is flattened. Also,canine teeth in humans do not overlapas they do in chimpanzees. And becausehumans walk upright, the place wherethe spine connects to the skull is morecentered under the skull in humans.


Apes and ChimpanzeesScientists think that the chimpanzee, a type of ape, is theclosest living relative of humans. This theory does not meanhumans descended from chimpanzees. It means that humansand chimpanzees share a common ancestor. Sometime between6 million and 30 million years ago, the ancestors of humans,chimpanzees, and other apes began to evolve along differentlines.

HominidsHumans are in a family separate from other primates. Thisfamily, called hominids,hominids, includes only humans and their human-like ancestors. The main characteristic that separates hominidsfrom other primates is bipedalism. Bipedalism means “walkingprimarily upright on two feet.” Evidence of bipedalism can beseen in a primate’s skeletal structure. Figure 2 shows a com-parison of the skeletal features of apes and hominids.

✓✓Reading Check In which family are humans classified?(See the Appendix for answers to Reading Checks.)

The gorilla pelvis tilts the ape’s large rib cage and heavy neck and head forward. The gorilla spine is curved in a C shape. The arms are long to provide balance on the ground.

The bones of gorillas (a type of ape) and humans (a type of hominid) have a very similar form, but the human skeleton is adapted for walking upright.

The human pelvis is vertical and helps hold the entire skeleton upright. The human spine is curved in an S shape. The arms are shorter than the legs.

Figure 2 Comparison of Primate Skeletons

hominidhominid a type of primate charac-terized by bipedalism, relatively long lower limbs, and lack of a tail

Discussion -----------------------------------gComparing Primates Display apicture of an ape and a pictureof a human for students to com-pare. Have students identifycharacteristics that the twoorganisms have in common.(Answers will probably include references to common physicalcharacteristics.) Then, ask stu-dents how the two animals aredifferent from each other.(Answers will probably include ref-erences to differences in behavioror abilities.) l Visual/Verbal

Using the Figure------gBinocular Vison Discuss withstudents how binocular vision,illustrated in Figure 1, is impor-tant. How is it useful tohumans? How is it different inmost other animals? (Sampleanswer: Binocular vision enableshumans to perceive depth and thusto judge distances, to hunt, to usetools, to drive vehicles, and to playsports. Except for some predators,most other animals do not havesuch abilities.) l Visual


the hominid family

vv--------------------------------------g

Exploring Vision Students canexplore the utility of binocularvision by making a dot on asheet of paper and placing thepaper on a desktop. Have themstand about half a meter awayfrom the desk and close theirright eye. Then, have them try totouch the dot on the paper withthe tip of a pencil. Have themrepeat the action with their lefteye closed and then with botheyes open. (It should be easier totouch the dot with both eyes openthan with one eyeclosed.) l Visual ee

CONNECTION toCONNECTION toAnthropology -----------------------------a

Bipedalism The tendency to walk fullyupright distinguishes us from apes. Buthow do our physical features relate to ourposture? Thomas Greiner, a physicalanthropologist, developed a computermodel that shows how muscle actionrelates to bone shape. Greiner concludedthat in order to regularly walk upright, anape would need larger gluteus maximusmuscles and a larger ileum. These attributesare seen in human bodies.

SUPPORT FOR

English Language LearnersWord Web Students will better under-stand the characteristics of homo sapiensif they are represented graphically. Askpairs of students to create a word webfor each homo sapiens trait they learn inthis section. The webs should includeany terms they know that connect tothe new trait. For example, the web forbipedal might include elements suchas two legs, two feet, stand up, walk, etc.Evaluate webs based on the numberand appropriateness of the connectingwords.l Visual/Verbal Section 3 • Humans and Other Primates 207

Hominids Through TimeScientists are constantly filling in pieces of the homi nid fam-ily picture. They have found many different fossils of ancient hominids and have named at least 18 types of hominids. How-ever, scientists do not agree on the classification of every fossil. Fossils are classified as hominids when they share some of the characteristics of modern humans. But each type of hominid was unique in terms of size, the way it walked, the shape of its skull, and other characteristics.

The Earliest HominidsThe earliest hominids had traits that were more humanlike than apelike. These traits include the ability to walk upright as well as smaller teeth, flatter faces, and larger brains than earlier primates. The oldest hominid fossils have been found in Africa. So, scientists think homi nid evolution began in Africa. Figure 3 shows a fossil that may be from one of the earliest hominids. It is 6 million to 7 million years old.

✓Reading Check Where are the earliest hominid fossils found?

AustralopithecinesMany early hominids are classified asaustralopithecines (AW struh LOH PITH uh SEENS). Members of this group were similar to apes but were different from apes in several ways. For example, their brains were slightly larger than the brains of apes. Some of them may have used stone tools. They climbed trees but also walked on two legs.

Fossil evidence of australopithecines has been found in several places in Africa. The fossilized footprints in Figure 4 were prob-ably made by a member of this group over 3 million years ago. Some skeletons of aus-tralopithecines have been found near what appear to be simple tools.

Figure 4 Anthropologist Mary Leakey discovered these 3.6 million year old footprints in Tanzania, Africa.

Figure 3 This skull was found in the Sahel desert in Chad, Africa. The skull is estimated to be 6 million to 7 million years old.

vv--------------------------------------------------------b

Primate Characteristics Helpstudents identify the charac-teristics that distinguish pri-mates from other mammal groups. Show them pictures of primate and nonprimate mam-mals. Ask students to describe how the primates differ from the other animals. (Sample answer: Primates generally have flatter faces than nonprimates. Their eyes are located at the front of the head rather than at the sides, their snouts are small, and their fingers are flexible.) l Visual/Logical


Africa

GroupGroup vv -------g

Comparing Hominids Createand display a large table to com-pare the distinguishing charac-teristics of the primates and hominids discussed in this sec-tion. Column heads might include “Binocular vision,” “Bi-pedalism,” “Brain size,” “Tool use,” “Known locations,” and “Estimated dates.” Call on stu-dents to make additions to the table. l Logical/Verbal

oIn 1975, fossils of 13 hominids were found in Ethiopia by Donald Johansen, a contem-porary of Mary Leakey. These fossils dif-fered in body size and jaw shape. Some anthropologists think that the larger fossils represent the males and the smaller fossils represent the females of a particular spe-cies. Johansen and others believe that the differences indicate that the fossils are of two distinct species of australopithecines.

Is That a Fact!One of the most famous skeletons of an australopithecine was found by Donald Johansen in Ethiopia 1974 and was nicknamed “Lucy.” This nickname came from the Beatles’ hit song “Lucy in the Sky with Diamonds,” which was playing around the time when the fossil was discovered.


A Variety of Early HominidsMany australopithecines and other types of hominids lived atthe same time. Some australopithecines had slender bodies.They had humanlike jaws and teeth but had small, apelikeskulls. They probably lived in forests and grasslands and atea vegetarian diet. Scientists think that some of these types ofhominids may have been the ancestors of modern humans.

Some early hominids had large bodies and massive teethand jaws. They had a unique skull structure and relativelysmall brains. Most of these types of hominids lived in tropicalforests and probably ate tough plant material, such as roots.Scientists do not think that these large-bodied hominids arethe ancestors of modern humans.

Global HominidsAbout 2.4 million years ago, a new group of hominids appeared.These hominids were similar to the slender australopithecinesbut were more humanlike. These new hominids had larger andmore complex brains, rounder skulls, and flatter faces thanearly hominids. They showed advanced tool-making abilitiesand walked upright.

These new hominids were members of the group Homo,which includes modern humans. Fossil evidence indicatesthat several members of the Homo group existed at the sametime and on several continents. Members of this group wereprobably scavengers that ate a variety offoods. Some of these hominids may haveadapted to climate change by migratingand changing the way they lived.

An early member of this new group wasHomo habilis (HOH moh HAB uh luhs),which lived about 2.4 million years ago.About 1.8 million years ago, a hominidcalled Homo erectus (HOH moh i REKtuhs) appeared. This type of hominidcould grow as tall as modern humansdo. A museum creation of a member ofHomo erectus is shown in Figure 5. No oneknows what early hominids looked like.Scientists construct models based on skullsand other evidence.

Figure 5 Fossils of a hominidknown as Homo erectus have beenfound in Africa, Europe, and Asia.

Thumb Through This

1. Keep your thumbs frommoving by attaching themto the sides of your handswith tape.

2. Attempt each of the fol-lowing tasks: using apencil sharpener, usingscissors, tying your shoe-laces, buttoning buttons.

3. After each attempt, answerthe following questions:

a. Is the task more diffi-cult with an opposablethumb or without one?

b. Do you think you wouldcarry out this task on aregular basis if you didnot have an opposablethumb?

Answers toSchool-to-Home Activity

3. a. Answers may vary. Most ofthe tasks will probably bemore difficult without theuse of the thumb.

b. Answers may vary. Somepeople would not like to carryout such a difficult task on aregular basis.

Discussion -----------------------------------g

Analyzing Tools Homo habilisis thought to have made one ofthe oldest recognizable stonetools. The tool was a pebblewith some sharp edges. Ask stu-dents how they think the toolwas made. (Sample answer: Flakeswere chipped off the pebble tosharpen it.) l Verbal/Logical

CONNECTIONCONNECTION vvART ---------------------------------------------------------------------------------g

Sculpting Sculptors probablyhelped paleoanthropologistsdetermine the physical appear-ance of the hominid shown inFigure 5. Sculptors can applytheir knowledge of anatomyto reconstruct body features.Have students research howsculptors are called upon toreconstruct hominid faces andheads, based on skulls. Then,have interested students use clayto sculpt a model of the headof a hominid.l Kinesthetic ee

CONNECTION toCONNECTION toHistory ---------------------------------------------------------------g

Insulting Apes? Many cartoons in the19th century satir ized the idea thathumans are related to apes. In one suchcartoon, Henry Bergh, the founder of theSociety for the Prevention of Cruelty toAnimals, chided Charles Darwin for insult-ing apes by suggesting that they are relatedto humans. Suggest that students look forexamples of these historical cartoons.l Visual/Interpersonal

MISCONCEPTIONALERT

Students often misunderstand themeaning of the scientific name of thegenus Homo. This word comes fromthe greek word for “earth” or “ground”and was later used to mean “man” or“human being” in latin. In some otherwords, the word root homo- comes fromthe greek word meaning “same.”

Section 3 • Humans and Other Primates 209

Recent HominidsAs recently as 30,000 years ago, two types of hominids mayhave lived in the same areas at the same time. Both had thelargest brains of any hominids and made advanced tools, cloth-ing, and art. Scientists think that modern humans may havedescended from one of these two types of hominids.

NeanderthalsOne recent hominid is known as Neanderthal (nee AN duhr TAWL).Neanderthals lived in Europe and western Asia. They may havelived as early as 230,000 years ago. They hunted large animals,made fires, and wore clothing. They also may have cared forthe sick and elderly and buried their dead with cultural ritu-als. About 30,000 years ago, Neanderthals disappeared. No oneknows what caused their extinction.

Early and Modern HumansModern humans are classified as the species Homo sapiensHomo sapiens(HOH moh SAY pee UHNZ). The earliest Homo sapiens existedin Africa 100,000 to 160,000 years ago. The group migratedout of Africa sometime between 40,000 and 100,000 years ago.Compared with Neanderthals, Homo sapiens has a smaller andflatter face, and has a skull that is more rounded. Of all knownhominids, only Homo sapiens still exists.

Early Homo sapiens created large amounts of art. Earlyhumans produced sculptures, carvings, paintings, and cloth-ing such as that shown in Figure 6. The preserved villagesand burial grounds of early humans show that they had anorganized and complex society.

Homo sapiensHomo sapiens the species of hominids that includes modern humans and their closest ances-tors and that first appeared about 100,000 to 160,000 years ago

Figure 6 These photos show museum recreations of early Homo sapiens.

Reteaching -------------------------------------b

PORTFOLIO

Timeline Have stu-dents make a timeline

that shows the order of appear-ance of the primates discussedin the chapter. When studentshave finished their timelines,have them review the timelineof another student. l Visual

Quiz ---------------------------------------------------------------------g

Among primates, what isdistinctive about hominids?(The main characteristic that distin-guishes hominids from other pri-mates is walking upright on twolegs as their main way of movingaround.)

AlternativeAssessment ---------------------------a

Hominid Poster Have stu-dents construct a poster witha detailed timeline of theappearance of different typesof primates and hominids. Askstudents to include picturesand information about thedistinguishing characteristicsof each group. Encourage stu-dents to conduct additionalresearch to find the latestdiscoveries. l Visual/Logical

h-----------------------------g

Writing Future Scientists Have studentswrite a page from an anthro-pologist’s journal that will be

written 100,000 years in the future.Tellstudents that the anthropologist is study-ing an archaeological site that containsthe remains or traces of people fromtoday. Suggest that students describe thescientist’s thoughts and hypothesesabout the site.l Visual PORTFOLIO

A skull of a Homo sapiens who had den-tal problems was found in Zambia.There was a hole in one side of the skulland signs of a partially healed abscess.This skull was made famous by a writerwho imagined that the hole was causedby a bullet shot from an interplanetaryvisitor’s gun 120,000 years ago.



For a variety of links related to this

chapter, go to www.scilinks.org

SummarySummary

Time (mya)

Human

30 25 20 15 10 5 0

Chimpanzee

DC

B

A

Gorilla

Orangutan

Gibbon

Review

Drawing the Hominid Family TreeScientists review their hypotheses when they learn something new about a group of organisms and their related fossils. As more hominid fossils are discovered, there are more features to compare. Sometimes, scientists add details to the relationships they see between each group. Sometimes, new groups of homi-nids are recognized. Human evolution was once thought to be a line of descent from ancient primates to modern humans. But scientists now speak of a “tree” or even a “bush” to describe the evolution of various hominids in the fossil record.

✓Reading Check What is likely to happen when a new hominid fossil is discovered?

• Humans, apes, and monkeys are primates. Almost all primates have opposable thumbs and bi nocular vision.

• Hominids, a subgroup of primates, include humans and their humanlike ancestors. The oldest known hominid fossils may be 7 million years old.

• Early hominids included australopithecines and the Homo group.

• Early Homo sapiens did not differ very much from present -dayhumans. Homo sapiensis the only type of homi-nid living today.

Using Key Terms

1. Use each of the following words in the same sentence: primate,hominid, and Homo sapiens.


2. The unique characteristics of primates are

a. bipedalism and thumbs.b. opposable thumbs.c. opposable thumbs and

binocular vision.d. opposable toes and thumbs.

3. Describe the major evolutionary developments from early homi-nids to modern humans.

4. Compare members of the Homogroup with australopithecines.

Critical Thinking

5. Forming Hypotheses Suggestsome reasons why Neanderthals might have become extinct.

6. Making Inferences Imagine you are a scientist excavating an ancient campsite. What might you infer about the people who used the site if you found the charred bones of large animals and various stone blades among human fossils?

Interpreting Graphics

The figure below shows a possible ancestral relationships between humans and some modern apes. Use this figure to answer the questions that follow.

7. Which letter represents the ances-tor of all the apes?

8. To which living ape are gorillas most closely related?

Topic: Human EvolutionSciLinks code: HSM0769


Sample Answer: Scientists will review their ideas about the evolu-tion of hominids.


1. Sample answer: Homo sapiens isthe only living type of hominid but not the only living type of primate.

2. c3. walking upright, larger brains,

changed diet, using tools, and culture

4. Sample answer: Compared to australopithecines, Homo werelarger, had larger brains and different skull shapes, moved out of Africa and into other conti-nents, and used tools.

5. Sample answer: They may have been killed off by larger animals, or they may have run out of food and starved to extinction.

6. Sample answer: It is possible that the people had hunted ani-mals for food.

7. A8. chimpanzee

vv-------------------------------------------------a

Classifying Primates Have students find out the family or genus of the apes and hominids mentioned in this section.

• Apes: family Pongidae (great apes; includes orangutans, gorillas, chimpanzees)

• Hominids: family Hominidae• Australopithecines: genus Australopithecus

(slender) and genus Paranthropus (robust)• Homo group: genus Homo (includes species

Homo habilis, Homo erectus, Homo neander-thalensis, and Homo sapiens)l Verbal

CHAPTER RESOURCES


CRF • Section Quiz g • Section Review g • Vocabulary and Section Summary g • Critical Thinking a

Section 3 • Humans and Other Primates 211

Form a hypothesis to explainobservations of traces left byother organisms.

Design and conduct anexperiment to test one ofthese hypotheses.

Analyze and communicatethe results in a scientifi c way.

• ruler, metric or meterstick

• sand, slightly damp

• large box, at least 1 m2 orlarge enough to contain 3 or 4footprints

Mystery FootprintsSometimes, scientists find clues preserved in rocks that areevidence of the activities of organisms that lived thousands ofyears ago. Evidence such as preserved footprints can provideimportant information about an organism. Imagine that yourclass has been asked by a group of scientists to help studysome human footprints. These footprints were found embed-ded in rocks in an area just outside of town.

Ask a Question

1 Your teacher will give you some mystery footprints in sand.Examine the mystery footprints. Brainstorm what you mightlearn about the people who walked on this patch of sand.

Form a Hypothesis

2 As a class, formulate several testable hypotheses about thepeople who left the footprints. Form groups of three people,and choose one hypothesis for your group to investigate.

Test the Hypothesis

3 Draw a table for recording your data. For example, if you havetwo sets of mystery footprints, your table might look similar tothe one below.

Mystery FootprintsFootprint set 1 Footprint set 2

Length

Width

Depth of toe

Depth of heel

Length of stride

DO NONOTDO NOT

WRITRITE INNRITE IN

BOOOOKOOK

Using Scientifi c Methods

Lab

OBJECTIVES

MATERIALS

SAFETY

InquiryInquiry LabLab

Mystery Footprints

Teacher’s NotesTeacher’s Notes

Time RequiredTwo 45-minute class periods

Lab Ratings

rTeacher Prep fff

Student Set-Up ff

Concept Level ff

Clean Up ff

Preparation NotesTo set up this lab, you will needto either find a sandy area out-side or construct a long, shallowsandbox out of wood or card-board. You may prefer to per-form this activity outsidebecause it is likely to be messy.Ask a boy and a girl (preferablystudents who are not in yourscience class) or two adults, onemale and one female, to walkthrough the sand with their barefeet. The sand should be about16 cm deep, and the area to bewalked through should be longenough that three or four foot-prints can be seen in the sand.Slightly moistened sand willhold the best footprints. Youmay want to make the foot-prints more permanent by usingplaster of Paris. If you do nothave access to sand, look for atype of soil that will hold afootprint.

CHAPTER RESOURCES


CRF • Datasheet for Chapter Lab• Lab Notes and Answers

Technology

Classroom Videos• Lab Video

• The Half-Life of Pennies

InquiryInquiry LabLab

Maurine Marchani

Raymond Park Middle SchoolIndianapolis, Indiana

Holt Lab Generator CD-ROMSearch for any lab by topic, standard, difficulty level,or time. Edit any lab to fit your needs, or create yourown labs. Use the Lab Materials QuickList softwareto customize your lab materials list.

CLASSROOM

TESTED& APPRO

VED


4 With the help of your group, you may first want to analyze your own footprints to help you draw conclusions about the mystery footprints. For example, use a meterstick to measure your stride when you are running. Is your stride different when you are walking? What part of your foot touches the ground first when you are running? When you are running, which part of your footprint is deeper?

5 Make a list of the kind of footprint each differ-ent activity produces. For example, you might write, “When I am running, my footprints are deep near the toe area and 110 cm apart.”

Analyze the Results

1 Classifying Compare the data from your footprints with the data from the mystery foot-prints. How are the footprints alike? How are they different?

2 Identifying Patterns How many people do you think made the mystery footprints? Explain your interpretation.

3 Analyzing Data Can you tell if the mystery footprints were made by men, women, chil-dren, or a combination? Can you tell if they were standing still, walking, or running? Explain your interpretation.

Draw Conclusions

4 Drawing Conclusions Do your data support your hypothesis? Explain.

5 Evaluating Methods How could you improve your experiment?

Communicating Your DataSummarize your group’s con clusionsin a report for the scientists who

asked for your help. Begin by stating your hypothesis. Then, summarize the methods you used to study the footprints. Include the comparisons you made between your foot-prints and the mystery footprints. Add pictures if you wish. State your conclusions. Finally, offer some suggestions about how you could improve your investigation.

WRITING

SKILL

Chapter 8 • Chapter Lab 213

AnswersThe answers for this activity will depend on the footprints your students observe. Students should be able to compare their own activities with varia-tions in the footprints they leave. Then, they should be able to apply what they’ve learned to the mys-tery footprints.

Safety CautionRemind students to review all safety cautions and icons before beginning this lab activity. Supervise students during this activity. Provide students with ample space and a safe location to test walking and running on the sandy area. Remind each group of students to keep out of the way of others. Have students keep shoes, or at least socks, on while walking on the sandy area.

Lab NotesTell the students to imagine that a group of scientists wish to ana-lyze human footprints found in the rocks near fossilized remains and that the scientists have contacted the class to help with the investigation. The scientists want to know how the students intend to gather informa tion to make inferences about the humans who left the prints. Explain that a scientist should be able to make the same type of inferences about an organism from fresh tracks as from pre-served tracks. Use the mystery footprints in the sand to help students design investigations for gathering data. From the data, students can learn to draw inferences.

A large proportion of research on evolution depends on mak-ing scientific inferences and checking for corroboration among different sources of data. To conclude the laboratory expe-rience, lead the students in a discussion about the importance of large sets of data in helping scientists make inferences.

CHAPTER RESOURCESWorkbooks

Long-Term Projects & Research Ideas• A Horse Is a Horse a

Complete each of the following sen-tences by choosing the correct term from the word bank.

Precambrian time Paleozoic eraMesozoic era Cenozoic era

1 During , life is thought to have originated from nonliving matter.

2 The Age of Mammals refers to the .

3 The Age of Reptiles refers to the .

4 Plants colonized land during the .

For each pair of terms, explain how the meanings of the terms differ.

5 relative dating and absolute dating

6primates and hominids

Multiple Choice

7 If the half-life of an unstable element is 5,000 years, what percentage of the parent material will be left after 10,000 years?

a. 100%b. 75%c. 50%d. 25%

8 The fi rst cells on Earth appeared in

a. Precambrian time.b. the Paleozoic era.c. the Mesozoic era.d. the Cenozoic era.

9 In which era are we currently living?

a. Precambrian timeb. Paleozoic erac. Mesozoic erad. Cenozoic era

0 Scientists think that the closest living relatives of humans are

a. lemurs.b. monkeys.c. gorillas.d. chimpanzees.

Short Answer

q Describe how plant and animal remains can become fossils.

w What information do fossils provide about the history of life?

e List three important steps in the early development of life on Earth.

r List two important groups of organ-isms that appeared during each of the three most recent geologic eras.

t Describe the event that scientists think caused the mass extinction at the end of the Mesozoic era.

UNDERSTANDING KEY IDEAS

USING KEY TERMS


ANSWERS

Using Key Terms1. Precambrian time2. Cenozoic era3. Mesozoic era4. Paleozoic era5. Absolute dating tries to

determine a specific range of dates, while relative dating determines the order of events but not specific dates.

6. Hominids are a type of pri-mate, but not all primates are hominids.

Understanding Key Ideas7. d8. a9. d

10. d

Assignment GuideSECTION QUESTIONS

1 5, 7, 11, 12, 20–22, 26, 27

2 1–4, 8, 9, 13–16, 19, 23, 24

3 6, 10, 17–19, 25

11. Sample answer: The remains of organisms can become fossils when geologic pro-cesses preserve them or their traces. An example is sediment covering an organism and the shape becoming hardened into rock.

12. Fossils tell us about the kinds of organisms that existed and the way they changed over time.

13. Simple chemicals reacted to form the molecules that make up life. Simple cells formed. Photosynthetic cells developed and began to produce oxygen.

14. Sample answer: Precambrian: prokaryotes and eukaryotes; Paleozoic: multicellular organisms, plants, insects, and amphibians; Mesozoic: dinosaurs and other reptiles, birds, and small mammals; Cenozoic: large mammals, including humans, and more-diverse birds and insects

15. A giant meteorite hit the Earth, disturbing ecosystems and causing climate change.

y From which geologic era are fossilsmost commonly found?

u Describe two characteristics that areshared by all primates.

i Which hominid species is alive today?

oConcept Mapping Use the followingterms to create a concept map: Earth’shistory, humans, Paleozoic era, dinosaurs,Precambrian time, land plants, Mesozoicera, cyanobacteria, and Cenozoic era.

pApplying Concepts Can footprints befossils? Explain your answer.

aMaking Inferences If you fi nd rocklayers containing fi sh fossils in a des-ert, what can you infer about the his-tory of the desert?

sApplying Concepts Explain how anenvironmental change can threatenthe survival of a species. Give twoexamples.

dAnalyzing Ideas Why do scientiststhink the fi rst cells did not need oxy-gen to survive?

f Identifying Relationships How does theextinction that occurred at the end ofthe Mesozoic era relate to the Age ofMammals?

g Making Comparisons Make a tablelisting the similarities and differencesbetween australopithecines, earlymembers of the group Homo, andmodern members of the speciesHomo sapiens.

The graph below shows data aboutfossilized teeth that were found withina series of rock layers. Use this graphto answer the questions that follow.

h Which of the following statementsbest describes the information pre-sented in the graph?

a. Over time, the number of carnivoresdecreased and the number of herbi-vores increased.

b. Over time, the number of carnivoresincreased and the number of herbi-vores increased.

c. Over time, the number of carnivoresand herbivores remained the same.

d. Over time, the number of carnivoresincreased and the number of herbi-vores decreased.

j At what point did carnivore teethbegin to outnumber herbivore teeth?

a. between layer 1 and layer 2b. between layer 2 and layer 3c. between layer 3 and layer 4d. between layer 4 and layer 5

Num

ber of

tee

thRock layer

Oldest Youngest

1 2 3 4 5

600

500

400

300

200

100

Carnivore teeth Herbivore teeth

CRITICAL THINKING

INTERPRETING GRAPHICS

16. Fossils in the Cenozoic era aremost common because they arecloser to the surface of Earthand were formed more recently.

17. Primates have opposablethumbs that allow them tograsp objects, and they haveeyes positioned at the front oftheir heads that allow them totell how far away something is.

18. Homo sapiens

Critical Thinking19. An answer to this

exercise can befound at the endof this book.

20. yes; A footprint is a trace leftby an organism.

21. that the rocks there may haveonce been underwater

22. Sample answer: If an environ-ment changes suddenly, spe-cies may not be adapted tosurvive the change. Examplesmight be a sudden change froma hot to a cold climate or a sud-den change from a wet to a dryenvironment.

23. There was no oxygen availablewhen the first cells developed.

24. After the dinosaurs were wipedout (with the exception ofbirds), mammals were able totake their place in ecosystems.

25. Sample answer:

Australo-pithecines

Earlyhomo

Homosapiens

Bipedalism yes yes yes

Brains medium larger largest

Tools none some many

Art none none a lot

Knownlocations

Africa severalcontinents

world-wide

Interpreting Graphics26. d27. b

CHAPTER RESOURCES


CRF • Chapter Reviewg• Chapter Test Ag• Chapter Test Ba• Chapter Test Cs• Vocabulary Activityg

Workbooks

Study Guide• Study Guide also available in Spanish.

Chapter 8 • Chapter Review 215

READINGRead each of the passages below. Then, answer the questions that follow each passage. Decide which is the best answer to each question.

Passage 1 In 1995, paleontologist Paul Sereno and his team were working in an unexplored region of Morocco when they made an incred-ible find—an enormous dinosaur skull! The skull measured about 1.6 m in length, which is about the height of a refrigerator. Given the size of the skull, Sereno concluded that the skeleton of the entire animal must have been about 14 m long—about as big as a school bus, and even larger than Tyrannosaurus rex. This 90-million-year-old preda-tor most likely chased other dinosaurs by running on large, powerful hind legs, and its bladelike teeth meant certain death for its prey. Sereno named his new discovery Carcharodontosaurus saharicus,which means “shark-toothed reptile from the Sahara.”

1. Paul Sereno estimated the total size of this Carcharodontosaurus based on

A the size of Tyrannosaurus rex.B the fact that it was a predator.C the fact that it had bladelike teeth.D the fact that its skull was 1.6 m long.

2. Which of the following is evidence that the Carcharodontosaurus was a predator?

F It had bladelike teeth.G It had a large skeleton.H It was found with the bones of a smaller

animal nearby.I It is 90 million years old.

3. Which of the following is a fact in the passage?

A Carcharodontosaurus was the largest predator that ever existed.

B Carcharodontosaurus had bladelike teeth.C Carcharodontosaurus was as large as

Tyrannosaurus rex.D Carcharodontosaurus was a shark-like reptile.

Passage 2 In 1912, Alfred Wegener proposed a hypothesis called continental drift. At the time, many scientists laughed at his idea. Yet Wegener’s idea jolted the very foundations of geology.

Wegener used rock, fossil, and glacial evidence from opposite sides of the Atlantic Ocean to support the idea that continents can “drift.” For example, Wegener recognized similar rocks and rock structures in the Appalachian Mountains and the Scottish Highlands, as well as similarities between rock layers in South Africa and Brazil. He thought that these striking similarities could be explained only if these geologic features were once part of the same continent. Wegener proposed that because continents are less dense, they float on top of the denser rock of the ocean floor.

Although continental drift explained many of Wegener’s observations, he could not find evi-dence to explain exactly how continents move. But by the 1960s, this evidence was found and continental drift was well understood. However, Wegener’s contributions went unrecognized until years after his death.

1. Which of the following did Wegener use as evidence to support his hypothesis?

A similarities between nearby rock layersB similarities between rock layers in different

parts of the worldC a hypothesis that continents fl oatD an explanation of how continents move

2. Which of the following statements is supported by the above passage?

F A hypothesis is never proven.G A new hypothesis may take many years to

be accepted by scientists.H The hypothesis of continental drift was not

supported by evidence.I Wegener’s hypothesis was proven wrong.


Answers to the standardized test preparation can help you identify student misconcep-tions and misunderstandings.

Teacher’s NoteTeacher’s NoteTo provide practice under more realistic testing conditions, give students 20 minutes to answer all of the questions in this Standardized Test Preparation.

Passage 11. D2. F3. B

Question 2: The answer is drawn by inference from the fourth sentence in the passage, “. . . its bladelike teeth meant certain death for its prey.” Students who miss this question may have missed the implication or may have difficulty with long sentences.

Question 3: The answer is drawn from the fourth sentence in the pas-sage. Answers A and C are false, given the facts in the passage. Students who chose answer D may have made an incorrect inference from the last sentence in the passage.

Passage 21. B2. G Question 1: The answer is drawn from the sec-

ond paragraph in the passage. Students who missed this question may have failed to distinguish between evidence that supports a hypothesis and other ideas presented in the passage. Answer A is an idea not present in the passage.

Question 2: The answer requires logical rea-soning and an inference of the main idea of the passage. Answers H and I are logically inconsis-tent with the passage. Answer F is a true state-ment but not supported by the passage.

READING

MISCONCEPTIONALERT

Sta

nd

ard

ize

d Te

st Pre

pa

ratio

n

1. Mesosaurus was a small, aquatic reptile and Glossopteris was an ancient plant species. What do these two have in common?

A Their fossils have been found on several continents.

B Their fossils are found in exactly the same places.

C Their fossils have been found only in North America.

D Their fossils have only been found near oceans.

2. Which of the following statements is best supported by these fi ndings?

F All of the continents were once connected to each other.

G South America was once connected to Africa.

H Glossopteris is adapted to life at the South Pole.

I Mesosaurus could swim.

3. The map provides evidence that the following continents were once connected to each other, with the exception of

A North America.

B Africa.

C Antarctica.

D South America.

1. Four students are sharing a birthday cake. The fi rst student takes half of the cake. The second student take half of what remains of the cake. Then, the third student takes half of what remains of the cake. What fraction of the cake is left for the fourth student?

A 1/2

B 1/4

C 1/8

D 1/16

2. One sixteenth is equal to what percentage?

F 6.25%

G 12.5%

H 25%

I 50%

3. What is one-half of one-fourth?

A 1/2

B 1/4

C 1/8

D 1/16

4. Half-life is the time it takes for one-half of the radioactive atoms in a rock sample to decay, or change into different atoms. Carbon-14 is a radioactive isotope with a half-life of 5,730 years. In a sample that is 11,460 years old, what percentage of carbon-14 from the original sample would remain?

F 100%

G 50%

H 25%

I 12.5%

5. If a sample contains an isotope with a half-life of 10,000 years, how old would the sample be if 1/8 of the original isotope remained in the sample?

A 5,000 years

B 10,000 years

C 20,000 years

D 30,000 years

Read each question below, and choose the best answer.

North�America

Eurasia

Africa

South�America

Australia

India

Antarctica

Glossopteris

Mesosaurus

Fossils of Glossopteris�and Mesosaurus

N

W E

S

The map below shows the areas where fos-sils of certain organisms have been found. Use the map below to answer the questions that follow.

INTERPRETING GRAPHICS MATH

CHAPTER RESOURCES


CRF • Standardized Test Preparation g

State Resources

For specifi c resources for your state, visit go.hrw.com and type in the keyword HSMSTR.

INTERPRETING GRAPHICS1. A2. G3. A

Question 1: The answer requires careful viewing of the graphic to find information that supports the correct answer. Simply subsituting “the two kinds of shading” for “their fossils” in each statement makes the answer more apparent. Answer A is supported by observing the presence of shading on several continents. Answers B, C, and D are false, as indicated by observing locations where the shad-ing contradicts the statement.

Question 2: The answer requires the student to locate continents in the graphic that have no shading to indi-cate the presence of either type of fossil. Answers B, C, and D are each false because the continents listed do have some shading on them.

MATH1. C2. F3. C4. H5. D

Question 1: This question is equivalent to the following problem:

1 � 1/2 � 1/2 � 1/2

Students who miss this question may have difficulty conceptualizing frac-tions of fractions or may have multi-plied by 1/2 an incorrect number of times.

Chapter 8 • Standardized Test Preparation 217

in Action

in Action

Social Studies Research an area where there is a debate over what to do with

fossils or remains of human ancestors. Write a newspaper article about the issue. Be sure to present all sides of the debate.

MathThe average volume of a Neanderthal adult’s brain was about 1,400 cm3, while that of an adult gorilla is about 400 cm3.Calculate how much larger a Neanderthal brain was than a gorilla brain. Express your answer as a percentage.

WRITING

SKILL

Residents of this neighborhood in Jerusalem, Israel, objected when anthropologists started to dig in the area.

Science, Technology, and SocietyUsing Computers to Examine Fossils Paleontologists want to examine fossils without taking apart or damaging the fossils. Fortunately, they can now use a technology called computerized axial tomography, or CAT scanning, which provides views inside objects without touching the objects. A CAT scan is a series of cross-section pictures of an object. A computer can assemble these “slices” to create a three-dimensional pic-ture of the entire object. Computer graphic programs can also be used to move pictures of fossil pieces around to see how the pieces fit together. The fossil skull above was recon-structed using CAT scans and computers.

Scientific DebateWho Owns the Past?Does a piece of land include all the layers below it? If you start digging, you may find evidence of past life. In areas that have been inhabited by human ancestors, you may find artifacts that they left behind. But who has the right to dig up these “leftovers” from the past? And who owns them?

In areas that contain many remains of the past, digging up land often leads to conflicts. Landowners may want to build on their own land. But when remains of ancient human cultures are found, living relatives of those cultures may lay claim to the remains. Scientists are often caught in the middle, because they want to study and preserve evidence of past life.

Science, Technology,

and Society

BackgroundThe computer-generated skull image is reconstructed from the fossil skull of a Neanderthal child. The fossil find is named Le Moustier 1; it was excavated from a cave in Le Moustier, France. This site is also impor-tant because of the unique types of tools found there. The tools indicate a different form of tool-making than is found in many other Neanderthal sites. One theory related to this finding is that Neanderthals learned new toolmaking techniques from Homo sapiens at some point when the two groups came in contact.

Scientific Debate

Discussion --------------------------------- GENERAL

Ask students to discuss what they might do if human fossils were discovered in their back-yard. Then, discuss a scenario in which a company is prevented or delayed from conducting business when human fossils are discovered on their property. Brainstorm other similar sce-narios or research and discuss real scenarios with which the students might be familiar. Ask students to think of ways that these conflicts might be resolved. Answer to Math Activity

350%Sample calculation:1,400 � 400 � 3.53.5 � 100% � 350%

Answer to Social Studies Activity

Student articles should reflect journalistic style, being both interesting and objective. Check that students have presented more than one side of the issue they have chosen. Almost any large urban area will have some notable archaeologi-cal or paleontological sites, and efforts to exca-vate the sites are often inconvenient to someone. However, if students need help selecting an area, suggest one of the following locations: New York City, New York; Miami, Florida; Rome, Italy; Athens, Greece; Island of Brac, Croatia; Jerusalem, Israel; Ayodhya, India; Kathmandhu, Nepal; or Yangtze River, China.


Language Arts

Visit the library and

look for a book by or about the Leakey family and other scientists who have worked with them. Write a short book review to encourage your class-mates to read the book.

To learn more about these Science in Action topics, visitgo.hrw.com and type in thekeyword HL5HISF.

Check out Current Science®

articles related to this chapter by visiting go.hrw.com. Just type in the keyword HL5CS08.

The Leakey FamilyA Family of Fossil Hunters In some families, a business is passed down from one generation to the next. For the Leakey’s, the family business is paleoanthropology (PAY lee OH AN thruh PAWL uh jee) —the study of the origin of humans. The first famous Leakey was Dr. Louis Leakey, who was known for his hominid fossil discover-ies in Africa in the 1950s. Louis formed many important hypotheses about human evolution. Louis’ wife, Mary, made some of the most-important hominid fossil finds of her day.

Louis and Mary’s son, Richard, carried on the family tradition of fos-sil hunting. He found his first fossil, which was of an extinct pig, when he was six years old. As a young man, he went on safari expeditions in which he collected photographs and specimens of African wildlife. Later, he met and married a zoologist named Meave. The photo at right shows Richard (right), Meave (left), and their daughter Louise (middle) Each of the Leakeys has contrib-uted important finds to the study of ancient hominids.

WRITING

SKILL

Answer to Language Arts Activity

Students can find numerous books about mem-bers of the Leakey family, books written by some of the Leakeys, and books about their col-leagues, such as Dian Fossey, Jane Goodall, Birute Galdikas, and Donald Johanson.

People In Science

BackgroundIn Africa, Richard Leakey may be more widely known for his strong beliefs in political rather than scientific arenas. He has organized and raised money for campaigns against the poaching of wildlife in Kenya. And in 1995, he founded a political party that opposes corruption in the Kenyan government. His political work has been contro-versial and at times dangerous, as he has received death threats and beatings from opponents.

vv------------------------------------- GENERAL

Have interested students research and make timelines of major discoveries in hominid evolution. Suggest that they include a map that pinpoints the location of each major dis-covery. They may wish to pre-sent their findings in a poster or Web page.

Chapter 8 • Science in Action 219

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