Goals■ Gather information about fossils

found in your area.■ Communicate details about fossils

found in your area.■ Synthesize information from

sources about the fossil record andthe changes in your area over time.

Go to the Glencoe Science Web site at tx.science.glencoe.com to get moreinformation about fossils and changesover geologic time and for data collected by other students.

Act A Head 1Use the InternetUse the InternetUse the InternetUse the Internet

Discovering the PastImagine what Texas was like millions of years ago. What animals might have been

roaming around the spot where you now sit? Can you picture a Tyrannosaurus rexroaming the area that is now Dinosaur National Park? The animals and plants thatonce inhabited your region might have left some clues to their identity—fossils. Sci-entists use fossils to piece together what Earth looked like in the geologic past.Fossilscan help determine whether an area used to be dry land or was underwater. Fossils canhelp uncover clues about how plants and animals have evolved over the course of time.Using the resources of the Internet and by sharing data with your peers, you can startto discover how North America has changed through time.

Recognize the ProblemHow has your area changed over geologic time?

Form a HypothesisHow might the area where you are now living have looked thousands or millions ofyears ago? Do you think that the types of animals and plants have changed muchover time? Form a hypothesis concerning the change in organisms andgeography from long ago to the present day in your area.

418 CHAPTER 14 Geologic Time

Fossil Name Plant or Age of Fossils Details About Plant Location of Additional Animal Fossil or Animal Fossil Fossil Information

Fossils in Your Area

Answers will vary.

Test Your Hypothesis

Analyze Your Data

Draw Conclusions

Do1. Make sure your teacher approves

your plan before you start.

2. Go to the GlencoeScience Web site attx.science.glen-coe.com to postyour data in thetable. Add any addi-tional informationyou think is impor-tant to understand-ing the fossils foundin your area.

Plan1. Determine the age of the rocks

that make up your area. Werethey formed during Precambriantime, the Paleozoic Era, the Meso-zoic Era, or the Cenozoic Era?

2. Gather information about the fossil plants and animals found inyour area during one of the above geologic time intervals. Find spe-cific information on when, whereand how the fossil organismslived. If no fossils are known fromyour area, find out informationabout the fossils found nearestyour area.

3. What other information did you discover about your area’sclimate or environment fromthe geologic time period youinvestigated?

1. What present-day relatives of prehis-toric animals or plants exist in your area?

2. How have the organisms in your areachanged over time? Is your hypothesissupported? Why or why not?

2. Describe the plant and animal fossils that have been discovered inyour area. What clues did you dis-cover about the environment of your fossil organisms? How do thesecompare to the environment of yourarea today?

3. Infer from the fossil organismsfound in your area what the geogra-phy and climate were like during thegeologic time period you chose.

1. Find this Use the Internet activity on the Glencoe Science Web site at tx.science.glencoe.com.Compare your data to those ofother students. Study other students’data to compare infor-mation about the geologic timeperiods and fossils that you inves-tigated. Review data that otherstudents have entered about fossils they have researched.

ACTIVITY 419

Extinct!Did you know…

…In 1865, when Lewis Carrollwrote about the dodo in his famous bookAlice in Wonderland, the bird had beengone for almost two hundred years fromthe island of Mauritius in the IndianOcean. First seen by European settlers in1507, the dodo was hunted for food. Thebirds were extinct by 1681.

…The earliest known gliding reptile had “wings” with a span of 30 cm that were wideflaps of flesh not attached to its limbs. From fossilsfound in Madagascar, scientists believe that

Coelurosauravus (see lor oh SOR uh vuhs)lived between 260 and 246 million years ago.

420 CHAPTER 14 Geologic Time

Saber-toothed cat

Coelurosauravus

…The saber-toothed cat lived in the Americas from about 1.6 million to 8,000 years ago. Smilodon, the best-known saber-toothed cat, was among themost ferocious carnivores. It had largecanine teeth, about 15 cm long, which itused to pierce the flesh of its prey.

1. If 75 species of organisms become extinct each day,how many would become extinct during a leap year?

2. How many years did it take from the first sighting of the dodo bird by Europeans until it became extinct?

3. What was the range between the smallest and largest wingspans among pterosaurs?

Go FurtherUse the Glencoe Science Web site at tx.science.glencoe.com to research

extinct animals, fish, birds, plants, and other life-forms. Trace the originsof each of the species and learn how long its kind existed on Earth.

SCIENCE STATS 421

…The first vertebrates to fly werereptiles called pterosaurs (TER uh sawrz).The front limbs of these reptiles developedinto wings during the Triassic Period. Theirwingspans ranged from 1.8 m to more than12 m. Some pterosaurs were fish eaters, fly-ing low over water to catch fish with theirnarrow jaws.

20 40 6010 30 50 70Percent extinction

Late Ordovician

Late Devonian

Late Permian

Late Triassic

Late Cretaceous

Perio

ds

Great Mass Extinctions of Species

Pterosaurus

…The woolly mammoth lived in the cold tundra regions during the Ice Age. It looked rather like an elephant with long hair, had a mass between 5,300 kg and 7,300 kg, and was between 3 m and 4 m tall.

Woollymammoth

422 CHAPTER STUDY GUIDE

4. At the end of the Paleozoic Era, manymarine invertebrates became extinct. Whatkind of marine organism is shown here?

Section 3 Middle and Recent Earth History

1. Reptiles and gymnosperms were dominantland life-forms in the Mesozoic Era. Mam-mals and angiosperms began to dominatethe land in the Cenozoic Era.

2. Pangaea broke apart during the MesozoicEra. Many mountain ranges formed duringthe Cenozoic.

3. Homo sapiensappeared duringthe PleistoceneEpoch. How mightHomo sapiens havecontributed to theextinction of ani-mals like the oneshown here?

Section 1 Life and Geologic Time1. Geologic time is divided into eons, eras,

periods, and epochs.

2. Divisions within the geologic time scale arebased largely on major evolutionarychanges in organisms.

3. Plate movements cause changes that affectorganic evolution. How can the building ofmountains like those shown here affect theevolution of species?

Section 2 Early Earth History1. Cyanobacteria were an early form of life

that evolved during Precambrian time.Trilobites, fish, and corals were abundantduring the Paleozoic Era.

2. Plants and animals began to move ontoland during the middle of the Paleozoic Era. Land plants and animals then evolvedrapidly and colonized the land.

3. The Paleozoic Era was a time of mountainbuilding. The Appalachian Mountainsformed when several islands and finallyAfrica collided with North America.

To help you review geolog-ical time, use the Organi-zational Study Fold you

made at the beginning of the chapter.

After You ReadFOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Study GuideChapter XXXX Study GuideChapter 1414

CHAPTER STUDY GUIDE 423

Vocabulary Wordsa. Cenozoic Era i. organic evolutionb. cyanobacteria j. Paleozoic Erac. eon k. Pangaead. epoch l. periode. era m. Precambrian timef. geologic time scale n. speciesg. Mesozoic Era o. trilobiteh. natural selection

Using VocabularyThe sentences below include vocabulary

words that have been used incorrectly. Changethe incorrect word so that the sentence reads correctly.

1. A change in the hereditary features of aspecies over a long period is extinction.

2. A record of events in Earth history is natural selection.

3. The largest subdivision of geologic time is the period.

4. The process by which the best-suited individuals survive in their environment is organic evolution.

5. A group of individuals that normally breedonly among themselves is an epoch.

Outline the chapters to make sure that you’reunderstanding the key ideas. Writing down themain points of the chapter will help you rememberimportant details and understand larger themes.

Study Tip

Complete the concept map on geologic time using the following choices: Cenozoic, Trilobites inoceans, mammals common, Paleozoic, Dinosaurs roam Earth, and Abundant gymnosperms.

Study GuideChapter XXXX Study GuideChapter 1414

Trilobites in oceans

First landplants

Paleozoic

Animal Plant

early life

Dinosaursroam Earth

Abundant gymnosperms

Mesozoic

Animal Plant

middle life

Mammals common

Abundantangiosperms

Cenozoic

Animal Plant

recent life

Eras

Choose the word or phrase that best completesthe sentence.

1. How many millions of years ago did the erain which you live begin? A) 650 C) 1.6B) 245 D) 65

2. What is the process by which better-suitedorganisms survive and reproduce? A) endangerment C) gymnospermB) extinction D) natural selection

3. What is the next smaller division ofgeologic time after the era? A) period C) epochB) stage D) eon

4. When did the most recent ice age occur? A) Pennsylvanian C) TertiaryB) Triassic D) Quaternary

5. What was one of the earliest forms of lifeon Earth? A) gymnosperm C) angiospermB) cyanobacterium D) dinosaur

6. Which group of organisms evolved fromthe same ancestors as amphibians? A) trilobites C) angiospermsB) lungfish D) gymnosperms

7. During which era did the dinosaurs live? A) Mesozoic C) MioceneB) Paleozoic D) Cenozoic

8. Which type of plant has seeds without protective coverings? A) angiosperms C) gymnospermsB) flowering plants D) magnolias

9. Which group of plants evolved during theMesozoic Era and is the dominant plantgroup today? A) gymnosperms C) ginkgoesB) angiosperms D) algae

424 CHAPTER ASSESSMENT

CA

D

B

Assessment & ReviewChapter 1515 Assessment & ReviewChapter 1414

10. When did the Ediacaran fauna live?A) Precambrian time C) Mesozoic EraB) Paleozoic Era D) Cenozoic Era

11. Why couldn’t plants move onto land untilan ozone layer formed?

12. Why are trilobites classified as index fossils?

13. What is the most significant differencebetween Precambrian life-forms and Paleo-zoic life-forms?

14. How is natural selection related to organicevolution?

15. In the early 1800s, a naturalist proposedthat the giraffe species has a long neck as aresult of years of stretching their necks toreach leaves in tall trees. Explain why thisisn’t true.

16. Interpreting Scientific Illustrations Thecircle graph below represents geologic time.Determine which interval of geologic timeis represented by each portion of the graph.Which interval was longest? Which do weknow the least about?

CHAPTER ASSESSMENT 425

17. Interpreting Data The Cenozoic Era haslasted 65 million years. What percentage ofEarth’s 4.5-billion-year history is that?

18. Comparing and Contrasting Use the out-lines of the present-day continents to makea sketch of Pangaea.

19. Forming Hypotheses Suggest some reasonswhy trilobites might have become extinct atthe end of the Paleozoic Era.

20. Interpreting Data A student found what hethought was a piece of dinosaur bone inPleistocene sediment. How likely is it thathe is right? Explain.

21. Make a Model In the Activity, you learnedhow a particular characteristic might evolvewithin a species. Modify the experimentalmodel by using color instead of height as acharacteristic. Design your activity with theunderstanding that varimals live in a dark-colored forest environment.

Go to the Glencoe Science Web site at tx.science.glencoe.com or use theGlencoe Science CD-ROM for additionalchapter assessment.

TECHNOLOGY

AssessmentChapter 1515

Many animals have inhabited Earth.Some of these animals have been dividedinto groups below. TEKS 8.2 C

Study the table and answer the followingquestions.

1. The animals in Group A are differentfrom the animals in Group B because only the animals in Group A are _____ .A) mammals C) amphibiansB) reptiles D) birds

2. The animals in Group B are differentfrom the animals in Group C because only the animals in Group B are _____ .F) dinosaurs H) amphibiansG) reptiles J) herbivores

3. The animals in all three groups aresimilar because _____ .A) They make their own food.B) They have hair.C) They must eat other organisms.D) They are meat eaters.

AssessmentChapter 1414

Group A Group B Group C

Saber-toothedcat

Giant ground sloth

Woollymammoth

Apatosaurus

Maiasaura

Tyrannosaurus

Frog

Turtle

Salamander

TAKS Practice

426 STANDARDIZED TEST PRACTICE

Precambrian portion of Earth’s history. Fossilevidence indicates that animals did not inhabitland until much later.

1. According to the passage, what type oforganism added oxygen to Earth’s earlyatmosphere? Reading TEKS 8.10 GA) VertebratesB) MammalsC) BacteriaD) Fungi

2. Which of these is the best summary of thispassage? Reading TEKS 8.10 GF) The earliest organisms lived in the ocean.G) The oldest rocks that have been found

with any evidence of life are about 3.5billion years old.

H) The production of oxygen by bacteria,which began nearly 3 billion years ago,helped make life on land possible.

J) Oxygen can act like a protective shield,blocking Earth’s surface from most ofthe incoming ultraviolet radiation.

3. What is the main idea of the fourth para-graph of this passage? Reading TEKS 8.10 FA) Oxygen entered the atmosphere.B) Oxygen from photosynthesis was very

important.C) Oxygen absorbed radiation from the Sun

to make ozone.D) The oldest rocks on Earth do not have

any fossils in them.

Read the passage. Then read each questionthat follows the passage. Decide which is the bestanswer to each question.

Life on EarthThe oldest rocks found on Earth have been

estimated to be about 4.0 billion years old. Butthese rocks do not contain any fossil remains.The oldest rocks that have been found with anyevidence of life are about 3.5 billion years old.These rocks have fossils of single-celled organ-isms that once lived in the oceans.

No life could have survived on land at thattime because there was so much ultraviolet radi-ation coming down to Earth’s surface from theSun. Early bacteria did something very impor-tant that made it possible for other species toinhabit Earth.

Scientists believe there was little oxygen inEarth’s early atmosphere. Nearly 3 billion yearsago, some early bacteria produced oxygen dur-ing photosynthesis. This oxygen bubbled intothe oceans, and after millions of years, enteredthe atmosphere.

This oxygen from photosynthesis was veryimportant. As it entered the atmosphere, someof it absorbed energy from the Sun’s radiation.The radiation caused chemical reactions, whichproduced ozone gas. This ozone began actingas a protective shield, blocking Earth’s surfacefrom most of the incoming ultraviolet radia-tion. As a result, it became possible for life tosurvive on land without being damaged byultraviolet radiation.

The fossil record provides clues about pastlife on Earth. The earliest large organisms livedin the oceans during the late part of the

TAKS Practice

Reading Comprehension

Test-Taking Tip Number the paragraphs in the passage to make sure that you are refer-ring to the correct paragraph when answering a question.

3. Which of the sequences below could fit intothe one shown in the picture above? ScienceTEKS 8.4 B

A) B)

C) D)

Consider this question carefully before writ-ing your answer on a separate sheet of paper.

4. The Himalayas are found at the boundarybetween two large continental plates. Thesemountains were formed as the result ofwhat geologic process? Science TEKS 8.14 A

Read each question and choose the bestanswer.

1. Which of these facts best explains why theoldest fossils have been discovered in sedi-ments that were deposited in ancient oceans?Science TEKS 8.2 DA) Only aquatic animals leave fossils.B) Fossils from land organisms have been

destroyed.C) The first life on Earth began in the

oceans.D) All living organisms need water.

2. The fossils found in layer G are consideredindex fossils by paleontologists. This meansthat _____. Science TEKS 8.2 CF) they are not as old as the fossils found in

layer MG) layer G is most likely the same age as

layer MH) it is the same age as the rock in layer LJ) the fossils are the oldest type found

on Earth

STANDARDIZED TEST PRACTICE 427

TAKS Practice

Test-Taking Tip Some answer choicesmight be true statements but not the best expla-nation to a particular question.

Test-Taking Tip Sedimentary rock layerscan be distinguished from each other in picturesby using different patterns to represent each layer.

Test-Taking Tip Index fossils appearedduring a specific block of time in Earth’s history.They can be used to date layers of rock.

Reasoning and Skills

Rock layers at Site X Rock layers at Site Z

K

L

MN

F

G

HJ

Test-Taking Tip Think about what happensas the continental plates move slowly overEarth’s plastic-like asthenosphere.