Focus on California Life Science 7th Grade Unit 2 - Chapter 8 Earth's History

Chapter Earth History Standards Preview Evidence from rocks us to understand the evolution of life on Earth . As a basis for understanding this a . Students know Earth today are similar to those that the past and slow have large effects over long ?

time . Students know the of life on Earth has been bY events , such as or the Impacts of Students know that the rock cycle the formation of new ment and rocks and that rocks are often found in layers , with the est generally on the bottom . Students know that evidence from layers and radioactive indicates Earth approximately year old and that lute on thus planet has for more than . Students know how movements of Earth continental and plates through time , with changes In and . us , have the past and present of Isms . Students know how to and of plant and on the ' scale A paleontologist examines a ized dinosaur skeleton in the Denver Museum of Nature and Science .

A Trip Through Geologic Time Focus on the BIG Idea How does evidence from rocks help scientists understand Earth history ?

Check What You Know While hiking , you find a rock containing a small fossil . The fossil looks like the shell of a clam . When this fossilized organism was alive , what kind of environment existed in the area where you are hiking ?

Explain your answer . Fossil brachiopod A Chapter 263 Science The images shown here represent some of the key terms in this chapter . You can use this vocabulary skill to help you understand the meaning of some key terms in this chapter . Use Clues to Determine Meaning 59 In this textbook . important new words , or key terms , first appear in dark type with a yellow highlight . The meanings , or definitions , of these words usually follow the new terms . In addition to the definitions themselves , there are often other clues that help you understand the meanings . The example below key term relative age . What relative age means The relative age of a rock is its age compared to the ages of other rocks . You have probably used the idea of relative age when your age with someone age , such as i a ' the age of an older brother or younger sister . The relative age of a rock does not give the exact number in years since the rock was formed . what the term does not mean Apply It ! In your own words . explain what means . what familiar example Is relative age compared to ?

Chapter Vocabulary Section ( page 253 ) geology erosion uniformitarianism igneous rock sedimentary rock metamorphic rock rock cycle magma igneous rock . page 272 ) relative age intrusion absolute age fault law of unconformity inclusion ' index fossil Section ( page 279 ) atom element radioactive decay Section ( page 283 ) plate theory of plate tectonics continental drift Section ( page 286 ) geologic time amphibian scale reptile era mass extinction mammal invertebrate vertebrate mass Build Science Vocabulary Online Visit Web Code

! to lead , Reading Create Outlines In an outline , you show the relationship between main ideas and supporting ideas . An outline is usually set up like the example shown below . Roman numerals show the main topics . Capital letters and regular numerals show the . Use the headings , key concepts , and key terms to help you decide what to Include in your outline . Look at the sample outline for part of Section . Hutton Big Idea key terms . Structure or Earth . definitions . Forces that shape Earth of rock processes ' also happened In past In your own II . Types of Rocks wow , Apply It ! What is the first main topic in the outline above ?

What are the three under this main topic ?

Compare the definition of uniformitarianism in the outline to the definition in Section . How are they similar ?

How are they different ?

Complete the outline above for Section in this chapter . Create an outline for Section in this chapter .

1533 Standards Investigation A Journey Through Geologic Time This chapter will take you on a journey through geologic time . You will learn how fossils reveal the history of life on Earth . To guide you on yourjourney , you and your classmates will make a timeline showing the many periods of geologic time . Your Goal To become an expert on one geologic time period and assist in constructing a timeline To complete this investigation , you must research a geologic time period of your choice create a travel brochure that shows what life was like in this time period illustrate your time period for the timeline follow the safety guidelines in Appendix A Plan It ! Begin by selecting a time period you would like to investigate . Check with your teacher to be sure that all the time periods will be covered by members of your class . Then , collect information on your time animals , plants , and environment . Use this information to write a travel brochure about ' your time period . Create illustrations that depict your time period and place them on the timeline . Use the travel brochure to present your geologic time period to your classmates . Chapters 267

Standards Focus Students know Earth today are similar to those that occurred in the past and slow geologic processes have large cumulative effects over long periods of time . Students know that the rock cycle includes the formation of new sediment and rocks and that rocks are often found in layers , with the oldest generally on the bottom . What is ?

What is the rock cycle ?

Key Terms geology erosion uniformitarianism igneous rock sedimentary rock metamorphic rock rock cycle magma lava the bread . Think It Over The Rock Cycle How Does Pressure Affect Particles of Rock ?

Place a sheet of paper over a slice of soft bread . Put a stack of several heavy books on top of the paper . After 10 minutes , remove the books . Observe what happened to . Slice the bread so you can observe its cross section . Carefully slice a piece of fresh bread and compare its cross section to that of the pressed bread . Observing How did the bread change after you removed the books ?

Describe the texture of the bread . How does the bread feel ?

What can you predict about how pressure affects rocks ?

Visitors to Badlands National Park in South Dakota see some of the strangest scenery on Earth . The park contains jagged peaks , steep cliffs , and deep canyons sculpted in colorful rock that is layered like a birthday cake . The layers of this cake are red , orange , pink , yellow , or tan . These rocks formed over lions of years as particles of mud , sand , and volcanic ash were deposited in thick layers . The mud and sand slowly changed to sedimentary rock . Then , uplift of the land exposed the rocks to the forces that wear away Earth surface . 2689 Badlands National Park A ' A Hutton Big Idea Geology is the study of the structure of planet Earth and the forces that make and shape Earth . The modern science of geology began in the late 17005 . James Hutton , a Scottish doctor and farmer , studied the rocks and landscape around him . He observed the structure of mountains and valleys . Hutton watched streams cutting through the land in the process of erosion . Erosion occurs when running water , ice , or wind break down rocks and carry the pieces away . After studying geologic in his own time , Hutton concluded that those same processes had occurred long ago .

Modern sand ripples Fossil sand ripples Hutton idea is called the principle of uniformitarianism ( yoo nuh for muh ee un iz um ) The principle of uniformitarianism states that the geologic processes that operate today also operated in the past . Ancient rocks can be understood by observing geologic processes . Hutton observed that most geologic processes happen very slowly . He inferred that these processes must have been at work for a very long time to produce such features as and deep valleys . Hutton concluded that Earth must be much older than was commonly thought in his time . Reading Who first proposed the principle of ) uniformitarianism ?

types of Rocks Geologists classify rocks into three main , sedimentary , and metamorphic . igneous rocks form when molten material from beneath Earth surface cools and ens . Igneous rock may form on or below Earth surface . Sedimentary rock is made of sediments that have been deposited and then pressed together to form solid rock Most sediments are tiny pieces of rocks and minerals . Sediments may also include the remains of plants or animals , such as leaves or shells . Most fossils are found in sedimentary rocks . Through fossils , geology provides evidence that supports the theory of evolution . Metamorphic rock forms when an existing rock is changed by heat , pressure , or chemical reactions . Most metamorphic rock forms under pressure deep underground . FIGURE Sand Ripples Ancient , fossilized sand ripples , are similar to sand ripples that form today . Applying Concepts What do the fossilized ripples tell you about conditions when the rocks formed Chapter 269

Erosion and deposition may produce layers of sedimentary rock . Heat and pressure can cause rocks to bend . FIGURE Processes That Change Rocks Processes such as volcanic activity and erosion can change rock from one kind to another . Relating Cause and Effect What factors cause sediments to become sedimentary rock ?

270 The Rock Cycle The rock cycle is a series of processes on and beneath Earth surface that slowly change rocks from one kind to another . Forces inside Earth and at the surface produce a rock cycle that builds , changes , and destroys rocks . The rock cycle is a very slow process , ing place over millions of years . Figure shows the rock cycle . Notice that it can follow many pathways . Volcanic Activity One possible pathway through the rock cycle begins with material beneath surface . As the magma is forced toward the surface , it may form a volcanic mountain . Some of the magma hardens underground , forming igneous rock , such as basalt or granite . Some of the magma onto the surface as lava . Erosion Over time , erosion wears away the mountain , exposing the igneous rock core . Rain and snow fall on the rock . Oxygen and other chemicals in the air react with minerals in the rock . These conditions break the rock into tiny particles . Water , ice , and wind then carry the particles away . Deposition Streams carry the particles of rock to the ocean . There they are deposited as sediment . Over lions of years , layers of sediment pile up on the ocean . The weight of the layers presses the sediments together . Chemicals in the water cement the particles together . Sedimentary rock such as sandstone is formed . Heat and Pressure As more and more sediments pile up on the sandstone , the sandstone becomes deeply buried . Pressure increases . The rock becomes hot . Heat and pressure change the rock texture from gritty to smooth . After millions of years , the sandstone is changed into a metamorphic rock such as quartzite . Melting The formation of metamorphic rock does not end the rock cycle . Forces inside Earth can push all three types of rock many kilometers beneath the face . There , intense heat and pressure melt the rock . This molten material can then form new igneous rock . And so the cycle continues .

guy OC Igneous , sedimentary , and ( art metamorphic rock change , continuously through the Vis ' Web Code . I , mung , Target Reading Skill create outlines Making Generalizations How does the rock Complete your outline of this section . Use your cycle relate to the principle of outline to help answer the questions below . Reviewing Key Concepts a . Defining What is uniformitarianism ?

Explaining How does uniformitarianism help geologists understand Earth history ?

Applying Concepts Do you think that earthquakes happened millions of years ago ?

Explain your answer . an . identifying What are the three types of rock ?

Explaining What is the rock cycle ?

Chapter 211 00 Standards Focus Students know that the rock cycle includes the formation of new sediment and rocks and that rocks are often found in layers . with the oldest generally on the bottom . What is the law of superposition ?

How do geologists determine the relative age of rocks ?

How are index fossils useful to geologists ?

Key Terms relative age absolute age law of superposition extrusion intrusion fault I unconformity inclusion index fossil The Relative Age of Rocks . Which Layer Is the Oldest ?

Make a stack of layers of clay . Each layer should be about the size and thickness of a pancake . If these flat layers are sediments , which layer of sediment was deposited first ?

Hint This is the oldest layer . Now form the stack into a dome by pressing it over a small rounded object , such as a small bowl . With a or plastic knife , carefully cut off the top of the dome . Look at the layers that you have exposed . Which layer is the oldest ?

Think It Over Inferring If you press the stack into a small bowl and trim away the clay that sticks above the edge , where will you find the oldest layer ?

As sedimentary rock forms , the remains of organisms in the sediment may become fossils . Millions of years later , if you split open the rock , you might see the bones of an extinct reptile or insect . Your first question about a new fossil might be , What is it ?

Your next question would probably be , How old is it ?

have two ways to express the age of a rock and any fossil it contains . The relative age of a rock is its age compared to the ages of other rocks . You have probably used the idea of relative age when comparing your age with someone elses age . For example , if you say that you are older than your brother but younger than your sister , you are describing your relative age . The relative age of a rock does not provide its lute age . The absolute age of a rock is the number of years since the rock formed . It may be to know a rock absolute age exactly . But sometimes geologists can determine a rock absolute age to within a certain number of years . The age of each family member could be given as relative age or absolute age .

The Position of Rock Layers . VII ' I Have you ever seen rock layers of different colors on a cliff A Trip Through Geologic Time beside a road ?

What are these layers , and how did they form ?

The sediment that forms sedimentary rocks is deposited in layers one on top of the other . Over time , the sediment and changes into sedimentary rock . These rock layers provide a record of Earths geologic history . It can be difficult to determine the absolute age of a rock . So geologists use a method to find a rock relative age . Geologists use the law of superposition to determine the relative ages of sedimentary rock layers . According to the law of position , in horizontal sedimentary rock layers the oldest layer is at the bottom . Each higher layer is younger than the layers below it . Relative dating only establishes the order in which rocks were . Scientists can not use the law of position to determine the absolute age of rocks . The walls of the Grand Canyon in Arizona illustrate the law FIGURE of superposition . You can see some of the rock layers found in The ' a the Grand Canyon in Figure . The deeper down you go in the 21 ) Grand Canyon , the older the rocks . Canyon . You can see five layers ' Why do sedimentary rocks have layers ?

clearly in the photograph . Applying Concepts In which labeled layers would you find the oldest fossils ?

Explain . Younger I rock layers Limestone 250 million years old 255 million years old Sunni Sandstone 235 million years old Chapter 273 Sampling a Sandwich Your teacher will give you a sandwich that represents rock layers in Earth crust . Use a round , hollow , uncooked noodle as a coring tool . Push the noodle through the layers of the sandwich . Pull the noodle out of the sandwich . Break the noodle gently to remove your core sample . Draw a picture of what you see in each layer of the core . Making Models Which layer of your sandwich is the oldest ?

The youngest ?

Why do you think scientists study core samples ?

274 FIGURE Faults and intrusions Faults and intrusions give clues to the relative ages of rocks . Rock layers are broken and shifted along a fault ( left ) An intrusion cuts through rock layers ( right ) Determining Relative Age There are other clues besides the position of rock layers to the relative ages of rocks . To determine relative age , geologists also study and intrusions of igneous rock , faults , gaps in the geologic record , and inclusions . Clues From Igneous Rock Igneous rock forms when magma or lava hardens . Magma is molten material beneath Earth surface . Magma that onto the surface is called lava . Lava that on the surface is called an extrusion . An extrusion is always younger than the rocks below it . Beneath the surface , magma may push into bodies of rock . There , the magma cools and hardens into a mass of igneous rock called an intrusion . An intrusion is always younger than the rock layers around and beneath it . Figure shows an intrusion . Geologists study where intrusions and formed in relation to other rock layers . This helps geologists understand the relative ages of the different types of rock . Clues From Faults More clues come from the study of faults . A fault is a break in Earth crust . Forces inside Earth cause movement of the rock on opposite sides of a fault . A fault is always younger than the rock it cuts through . To determine the relative age of a fault , geologists the relative age of the youngest layer cut by the fault . Movements along faults can make it harder for geologists to determine the relative ages of rock layers . You can see in how the rock layers no longer line up because of movement along the fault .

iv the cheese is like an intrusion . Look again at the igneous Relationships When geologists use noun , intrusions , or faults to date rocks , they apply the of relationships . That principle states i lfe ' when something cuts across a body of rock , that something , a , is younger than the rock it cuts across . layers then form on top . To understand this principle , think of a sandwich made from a roll and a slice of cheese . The roll must be made before can occur ?

the cheese can be put inside . The roll is like a body of rock , and sion in the photo on the right in Figure . The igneous sion is like a sandwich . Gaps in the Geologic Record The geologic record of rock layers is not always complete . Deposition slowly builds layer upon layer of sedimentary rock . But some of these layers may erode away , exposing an older rock surface . Then deposition begins again , building new rock layers . The surface where new rock layers meet a much older rock surface beneath them is called an . An mity is a gap in the geologic record . An unconformity shows where some rock layers have been lost because of erosion . Figure shows how an unconformity forms . What is an ?

Sedimentary rocks form in horizontal layers . Folding tilts the rock layers . Inclusions Inclusions can help date rocks when an mity is present . An inclusion is a piece of rock that is contained in another rock . Unlike an intrusion , which starts out as liquid magma , an inclusion starts as a solid rock piece that breaks off from an existing rock . Then , after a long time , the piece of rock becomes part of a second rock . The rock containing an inclusion is younger than the rock from which the inclusion came . Look at the bottom frame of Figure . Notice the in the bright pink layer . They broke off from the eroded surface of the unconformity . The rock pieces later became part of ments that were deposited on the eroded surface . These sediments , including the broken rock pieces , into sedimentary rock New sediment is deposited , forming rock layers above the unconformity . Notice the inclusions in the new rock . Chapter 215

FIGURE Looking for Fossils These scientists are removing fossils from rock layers . Applying Concepts How can fossils help geologists match rock layers ?

276 Using Fossils to Date Rocks To date rock layers . geologists first give a relative age to a layer of rock at one location . Then they can give the same age to matching layers of rock at other locations . Certain fossils , called index fossils , help geologists match rock layers . To be useful as an index fossil , a fossil must be widely distributed and represent a type of organism that existed only . A fossil is considered widely distributed if it occurs in many different areas Geologists look for index fossils in layers of rock . Index fossils are useful because they tell the relative ages of the rock layers in which they occur . Geologists use particular types of organisms as index example , certain types of ammonites . Ammonites ( AM uh ) were a group of animals . Ammonites evolved in shallow seas more than 500 million years ago and became extinct about 65 million years ago . Ammonite fossils make good index fossils for two reasons . First , they are widely distributed . Second , many different types of ammonites evolved and then became extinct after a few lion years . Geologists can identify the different types of through differences in the structure of their shells . Based on these differences , geologists can identify the rock layers in which a particular type of ammonite fossil occurs . You can use index fossils to match rock layers . Look at Figure , which shows rock layers from four different locations . Notice that two of the fossils are each found in only one of these rock layers . These are the index fossils Reading What characteristics must a fossil have to be useful ) as an index fossil ?

Ammonite fossils House . Using Index Fossils Go Scientists use index fossils to match up rock layers at locations ' that may be far apart . The ammonites in layer are index ( fossils . Interpreting Diagrams Can you another index For Index Fossils activities Visit Web Code fossil in the diagram ?

Hint Look for a fossil that occurs in only one layer but in several different locations . Assessment Vocabulary Skill Use Clues to Determine a . Defining What is an index fossil ?

Meaning Reread the of . Applying Concepts The fossil record shows identify two phrases that help you understand the that horseshoe crabs have existed with very meaning of extrusion . little change for about 200 million years . Would horseshoe crabs be useful as an index Key fossil ?

Explain why or why not . a . Defining In your own words , the terms relative age and absolute age . is . Explaining What is the law of superposition ?

At Ho I ii Activity Inferring A geologist a cliff where the edges of several different rock layers can be Drawer to the Past Collect ten items out of seen . Which layer is the oldest ?

Explain . a drawer full of odds and ends such as keys . a . Reviewing Besides the law of superposition , coins , receipts , photographs , and souvenirs . what are three types of clues to the relative Have your family members put them in order age of rock layers ?

from oldest to newest . What clues will you use . Comparing and Contrasting Compare and to determine their relative ages ?

DO YOU contrast and intrusions . the absolute age of any of the items ?

Sequencing An intrusion crosses an extrusion . Which layer is the older ?

Explain . chapters 217 It . Inferring Why are there no fossils in layers How can you use fossils and geologic features to and ?

interpret the relative ages of rock layers ?

i What kind ' Wild ' ayer . Skills Focus interpreting data , drawing conclusions Sue . Inferring Which layer at Site might have Procedure formed at the same time as layer at Site 27 . Study the rock layers at Sits and . Write , Interpreting Data what clues show an down the similarities and differences unconformity or gap in the horizontal rock between the layers at the two sites . layers ?

Which rock layers are missing ?

What . List the kinds of fossils that are found in each might have happened to these reek levers ?

rock layer of Sites and . Drawing Conclusions Which is older , sion or layer ?

How do you know ?

Analyze and . Communicating Write a journal entry describing how the environment at Site changed over time . Starting with the earliest . Interpreting Data What fossil clues in the ' the layers A and indicate the kind of ' am he ment that existed when these rock layers were formed ?

How did the environment change in layer ?

More to , which layer is the Draw a sketch similar to Site and include a fault ?

How ( 10 you know that cuts across the intrusion . Have a partner then identify the relative age of the fault , the . Drawing Conclusions Which of the layers intrusion and the layers by the fau . formed most recently ?

How do you know ?

an Standards Focus Students know that from geologic layers and radioactive indicates Earth is approximately billion years old and that life on this planet has existed for more than billion years . happens during radioactive decay ?

what can be learned from radioactive dating ?

What is the probable age of Earth ?

Key Terms atom element radioactive decay Stromatolites Scientists think that ancient stromatolites were formed by organisms similar to bacteria ( above ) Modern stromatolites ( right ) still form reefs along the western coast of Australia . Dating Standards How Long Till Gone ?

Make a small modeling clay . Carefully use a knife to cut the clay in half . Put one half of the clay aside . Cut the clay in half two more times . Each time you cut the clay , put one half of it aside . Think It Over Predicting How big will the remaining piece of clay be if you repeat the process several more times ?

In Australia , scientists have found sedimentary rocks that contain some of the world oldest fossils . These are fossils of stromatolites MAT uh ) Stromatolites are the remains of reefs built by organisms similar to bacteria . Sediment eventually covered these reefs . As the ment changed to rock , so did the reefs . Using absolute dating , scientists have determined that some stromatolites are more than billion years old . To understand absolute dating , you I need to learn more about the chemistry of rocks .

In i Energy and particles noun 10 Radioactive Decay In the process of radioactive decay , a parent atom releases energy and particles as it changes to a new kind of atom , a daughter atom . Focus it lhe of a radioactive element is the amount of time it takes for half of the radioactive atoms to decay . The of is billion years . Calculating After three how much of the radioactive element remains ?

2000 Radioactive Decay Rocks are a form of matter . All the matter you see , including rocks , is made of tiny particles called atoms . When all the atoms in a particular type of matter are the same , the matter is an element . Carbon , oxygen , iron , lead , and potassium are just some of the more than 110 currently known elements . Most elements are stable . They do not change under normal conditions . But some elements exist in forms that are unstable . Over time , these elements break down , or decay , by releasing particles and energy in a process called radioactive decay . These unstable elements are said to be radioactive . During the process of radioactive decay , the atoms of one element break down to form atoms of another element . Radioactive elements occur naturally in igneous rocks . use the rate at which these elements decay to calculate the rock age . You calculate your age based on a birthday . What the birthday of a rock ?

For an igneous rock , that birthday is when it first hardens to become rock . As a radioactive element within the igneous rock decays , it changes into another element . 50 the composition of the rock changes slowly over time . The amount of the radioactive element goes down . But the amount of the new element goes up . The rate of decay of each radioactive element is never changes . Scientists can measure it experimentally . This rate of decay is the elements . The of a active element is the time it takes for half of the radioactive atoms to decay . You can see in Figure 11 how a radioactive element decays over time . I what is the meaning of the term ?

Decay of Potassium 40 Key I ( parent isotope ) I ( isotope ) years ago years ago An Ci Elements Used in Radioactive Dating Radioactive Element ( years ) Range ( years ) billion 14 billion 713 million billion 10 billion 10 billion 10 billion Determining Absolute Ages Radioactive dating is used to determine the absolute ages of rocks . In radioactive dating , scientists measure the amount of a radioactive element ( the parent element ) in a mineral in a rock . Then they measure the amount of the stable element into which the radioactive element decays ( the daughter element ) By calculating the ratio of the radioactive element to the stable element . scientists can determine the age of the rock . Dating Scientists often date rocks using . This form of potassium decays to stable and has a life of billion years . is useful in dating the most ancient rocks because of its long . Dating A radioactive form of carbon is . All plants and animals contain carbon , including some . As plants and animals grow , carbon atoms are added to their tissues . After an organism dies , no more carbon is added . But the in the organism body decays . It changes to stable . To determine the age of a ple , scientists measure the amount of that is left in the organisms remains . From this amount , they can mine its absolute age . has been used to date fossils such as frozen mammoths , as well as pieces of wood and bone . is very useful in dating materials from plants and animals that lived up to about years ago . 14 has a of only years . For this reason , it can be used to date very ancient fossils or rocks . The amount of left would be too small to measure accurately . FIGURE 12 The of different radioactive elements vary greatly . Percentage What percentage of a radioactive element will be left after ?

First , multiply three times to what fraction of the element will remain . 2228 You can convert this fraction to a percentage by setting up a proportion a 100 To the value of , begin by cross multiplying , as ior any proportion 100 100 Practice Problems What , percentage of a radioactive element will remain after ?

231 How Old Is Earth ?

Scientists haven found it easy to out the age of planet Earth . Earth is always changing , through erosion and other . Most of the matter that made up early Earth has been destroyed or changed . Radioactive dating shows that the oldest rocks ever found on Earth are about billion years old . But hypothesize that Earth formed even earlier than that . Scientists have used moon rocks and meteorites to estimate the age of Earth . Meteorites are chunks of rocks from space that have hit Earth surface . According to one hypothesis , nouns 13 Earth , meteorites , and the moon are about the same age . When Rocks from the Moon Earth was very young , a large object from space collided with By determining the age of it . This collision threw a large amount of material from both rocks hay ?

inferred that bodies into orbit around Earth . Some of this material Earth IS about billion years old . to form the moon . In the 19705 , astronauts who visited the moon brought several moon rocks back to Earth . Scientists have used ( radioactive dating to determine the age of those moon rocks . Radioactive dating shows that the oldest moon rocks are , ad , omi , dating about billion years old . Scientists infer that Earth is only Visit a little older than those moon billion ?

years old . The oldest fossils of living things appear in geologic layers that are billion years old . Section Assessment Vocabulary Skill Use Clues to Determine Problem Solving A geologist finds a fossil Meaning Reread the of radioactive in a layer of sedimentary rock that lies in decay , and the text near the . In your between two igneous . How could own words . explain what radioactive decay means . the geologist determine the age of the fossil ?

a . Reviewing How old are the oldest rocks found on the moon ?

Explaining What do scientists estimate Earth age to be ?

Summarizing How were scientists able to infer Earth age ?

Reviewing Key Concepts a . Defining In your own words , the term radioactive element . Describing How does the composition of a rock containing a radioactive element change over time ?

Applying Concepts How is a radioactive element rate of decay like the ticking of , I ( a clock ?

Explain . Identifying What method do geologists use what percentage of a determine the ab ?

radioactive element will remain after Explaining Why is it difficult to determine ves ?

the absolute age of a sedimentary rock ?

2820 ' A Standards Focus ! Students know how move ments of Earth continental and oceanic plates through time , with associated changes in climate and geographic connections , have affected the past and present distribution of organisms . How does the theory of plate tectonics explain the movement of Earth landmasses ?

How has the movement of Earth plates affected organisms ?

Key Terms plate I theory of plate tectonics continental drift Movement of Earth Plates , Standards where Were the Fossils Found ?

is an animal that became extinct over 200 million years ago . Make labels by writing on two small notes . Fossils of have been found in Africa and South America . On a globe of the world , place one label on South America . Put the second label on Africa . Observe the distances that separate these labels . Think It Over would you expect fossils of the same extinct organism to be found on two different continents ?

Why or why not ?

Have you ever noticed that Earth landmasses resemble pieces of a giant jigsaw puzzle ?

its true . The east coast of South ica , for example , would nicely into the west coast of Africa . The Arabian Peninsula would fit fairly well with the em coast of Africa . Since the 16005 , people have wondered why Earth landmasses look as if they would together . After all , land can move . Or can it ?

14 Landmasses Fit Together The Arabian peninsula , which looks something like a foot , fits between the continents of Africa and Asia almost like a puzzle piece . 283 225 Million Years Ago Million Years Ago 135 Million Years Ago Earth Today Go For ( Drift activity Web Code Continental Drift The movement of the continents is one factor affecting the distribution of organisms . Interpreting Maps How has Australia location changed ?

Earth Plates outer layer consists of pieces that together like a jigsaw puzzle . This outer layer is made of more than a dozen major pieces called plates . Plate boundaries do not always lie along the edges of continents . The eastern boundary of the North can plate , for example , lies under the Atlantic Ocean . Scientists use the concept of plates to explain how landmasses have changed over time . The theory of plate tectonics states that Earth plates move slowly in various directions . The plates move , on average , about centimeters per year . Some plates slowly pull away from each other , some plates push toward each other , and some plates slide past each other . According to the theory of plate tectonics , landmasses have changed position over time because they are part of plates that are slowly moving . About 260 million years ago , all the continents were joined together in a continent called . Then , about 225 million years ago , the different continents began to drift apart . The very slow movement of continents is called continental drift . What is continental drift ?

Distribution of Organisms The movement of Banh plates has affected the evolution of ing things . As Earth plates moved . landmasses changed their locations . These changes affected where different kinds of organisms , past and present , are located . Climate As the plates move , the continents may move north and south . As the continents move . their climate may change . As the climate changes , so do the kinds of organisms that live on the continent . For example , millions of years ago , the North American plate was much closer to the equator than it is now . North America climate was warm and cal then . Huge ferns grew in forests . Plants such as those ancient ferns could not grow in North America today , because the climate is too cool .

FIGURE 16 Marsupials in Australia Because of continental drift , Australia became isolated . Today , most mammals in Australia , including this koala . are marsupials . Separation of Organisms As plates pulled apart , isms on different plates became separated from one another . Fossils of , a dinosaur , have been found in Europe , Africa , and North America . The locations of these suggest that those continents were once joined . Continental drift has also affected organisms that are alive today . When populations of organisms become widely rated , their genetic makeup may change in different ways . Therefore , the separated populations often evolve differently . Organisms in Australia have been isolated from all other organisms on Earth for millions of years . Unusual organisms have evolved in Australia . For example , most mammals in Australia are marsupials . Unlike other mammals , female marsupials have pouches in which their young develop after birth . In contrast , few marsupials exist on other continents . Writing , section ii Assessment Vocabulary Skin use due , to a . Reviewing What is continental drift ?

Meaning How does Figure 15 help you . Describing Describe how continental drift understand the meaning of continental ?

A Predicting Suppose that , millions of years Key from now , Australia moves so that it Identifying Name the theory that explains connects to South America , would Australia the movement of pieces of Earth surface . still have the same of mammals ?

Explaining Explain why the continent Explain your answer . of North America is not where it was 225 million years ago . Predicting In 250 million years , would you In Science expect North America to be where it is now ?

Look Explain your answer . youf dug go moved between 135 years ago and India moved . Chapter 285 Section Standards Focus Students know the history of life on Earth has been disrupted by major catastrophic events , such as major volcanic eruptions or the impacts of asteroids . Students know how to explain significant developments and extinctions of plant and animal life on the geologic time scale . why is the geologic time scale used to show Earth history ?

What were early Precambrian organisms like ?

What were the major events of the . and Eras ?

Key Terms geologic time scale era period invertebrate vertebrate amphibian reptile mass extinction mammal 2850 The Geologic Time Scale Standards Your Time Scale . Make a list of about 10 to 15 important events that you remember in your life . On a sheet of paper . draw a timeline to represent your life . Use a scale of to year . Write each event in the correct year along the timeline . Now divide the timeline into parts that describe major periods in your life , such as preschool years , elementary school years . and middle school years . Think It Over Making Models Along which part of your timeline are most of the events located ?

Which period of your life does this part of the timeline represent ?

Why do you think this is so ?

Imagine squeezing Earth history into a day . Earth forms at midnight . About seven hours later , the earliest organisms appear . Over the next 14 hours , simple , organisms such as and worms develop . A little after hours , more complex organisms evolve in the oceans . Reptiles and insects first appear about an hour after that . Dinosaurs arrive just before , but are extinct by Modern humans don appear until less than a second before midnight ! The Geologic Time Scale Months , years , or even centuries aren very helpful for ing about Earth long history . Because the time span of Earth past is so great , geologists use the geologic time scale to show Earth history . The geologic time scale is a record of the life forms and geologic events in Earth history . You can see in Figure 17 that the geologic time scale begins with Precambrian Time ( pree KAM bree un ) Precambrian Time covers about 88 percent of Earth history . After brian Time , the basic units of the geologic time scale are eras and periods . Eras are the three long units between brian Time and the present . Eras are subdivided into periods .

FIGURE 17 The Geologic Time Scale The eras and periods of the geologic time scale are used to date the events in Earth long history . Interpreting Diagrams How long ago did the Era end ?

Geologic Time Scale Millions ) Period of Years Ago ( millions of years ) Era The ( sen uh ik ) began about 66 million years ago and continues to the present The word part means recent . means Mammals became common during this time . Era People often call the ( uh ik ) the Age of Dinosaurs . The began about 245 million years ago and lasted about 180 million years . The word pan means . i Era The ( pay lee uh ik ) began about 544 million years ago and lasted for 300 million years . The word part means ancient or Chapter I 287

FIGURE 18 Early Earth This artist illustration shows Earth shortly after the moon formed . Notice the rocky objects from space striking Earth , and the molten rock flowing over the surface . Go For Links on Precambrian Earth Visit Web Code 288 Early Earth Precambrian Time begins when the Earth formed , about billion years ago . Scientists that early Earth was very hot . Over time , however , the outer layers cooled and became solid . ess than 500 million years after Earth tion . rock on the surface formed continents . At this time , the atmosphere , which is the blanket of gases rounding Earth , was made up mostly of the gases nitrogen . carbon dioxide , and water vapor . There was little oxygen . Scientists can not pinpoint when or where life began . But scientists have found fossils of organisms in rocks that formed about billion years ago . These earliest life forms were probably similar to bacteria . Unlike most organisms today , these organisms did not need oxygen . Scientists hypothesize that all other forms of life on Earth arose from these simple organisms . About billion years ago , many organisms began using energy from the sun to make their own food . This process is called photosynthesis . Among these early photosynthetic organisms were cyanobacteria . These bacteria . which were once called green algae , have been extremely successful . They are still alive today , and they have changed very little . One product of photosynthesis is oxygen . Organisms released oxygen into the atmosphere . The amount of oxygen in the air slowly increased . Processes in the atmosphere changed some of this oxygen into a form called ozone . The owne layer blocked out some of the ultraviolet rays of the sun . Shielded from the let rays , organisms could live on land .

The Era You have traveled in a time machine to the beginning of the Era . The time machine is now moving forward , toward the present . You are about to see a period of rapid change . The Cambrian Explosion In the Cambrian Period , life took a big leap forward . At the beginning of the Era , many different kinds of organisms evolved . Paleontologists call this event the Cambrian Explosion because so many new life forms appeared within a relatively short time ( approximately 30 million years ) For the time , many organisms had hard parts , including shells and outer skeletons . Many animals , such as sponges , and worms , were invertebrates . Invertebrates are animals without backbones . Scientists infer that at this time , all animals lived in the sea . Fossils provide evidence of a watery environment . That is because many Cambrian fossils are similar to modern sea mals . For example , were small animals with two shells . looked like modern clams . Therefore , like clams , probably lived in water . Vertebrates Arise During the Ordovician ( duh VISH ee un ) and Silurian ( ee un ) periods , invertebrates shared the seas with a new type of organism . lawless evolved . lawless were the first vertebrates . A vertebrate is an animal that has a backbone . These early had like mouths . FIGURE 19 The Cambrian Explosion During the early Cambrian period , Earth oceans were home to many strange organisms unlike any animals that are alive today . Chapter ! 289

20 Devonian Armored Paleontologists have found fossils of huge armored fish , like this , that lived during the Devonian Period . Life Reaches Land Until the Silurian Period . only organisms lived on the land . But during the Silurian Period , plants became abundant . These first . simple plants grew low to the ground in damp areas . By the Devonian Period ( von nee un ) plants that could grow in drier areas had evolved . Among these plants were the earliest ferns . The first insects also appeared during the Silurian Period . Both invertebrates and vertebrates lived in the Devonian seas . Even though the invertebrates were more numerous . the Devonian Period is often called the Age of Fishes . Every main group of was present in the oceans at this time . Most now had jaws , bony skeletons . and scales on their bodies . Some . like the one in Figure 20 , were huge . Sharks appeared in the late Devonian Period . During the Devonian Period , vertebrates began to invade the land . The first vertebrates to crawl onto land were with strong , The first amphibians evolved from these . An ee un ) is an animal that lives part of its life on land and part of its life in water . The Carboniferous Period Throughout the rest of the 21 The Coal Forest Forests of the Carboniferous Period later formed coal deposits . Predicting What types of fossils would you expect to find from the Carboniferous Period ?

life expanded over Earths continents . Other from the amphibians . For example . small tiles developed during the Carboniferous Period . Reptiles have scaly skin and lay eggs with tough , leathery shells . Some types of reptiles became very large during the later .

Dat Mass Extinctions The graph shows how the number of families of animals in Earth oceans has changed . Reading Graphs What variable is shown on the ?

On the of the graph ?

Interpreting Data How long ago did the ( most recent mass extinction occur ?

Interpreting Data Which mass extinction produced the greatest drop in the zoo too number of families of ocean animals ?

ye , Relating Cause and Effect In general , how did the number of families change i between mass extinctions ?

During the Carboniferous Period , winged insects evolved into many forms , including huge . Giant ferns and plants formed vast swampy forests called coal The remains of these plants formed thick deposits of sediment that changed into coal over millions of years . Mass Extinction Ends the At the end of the Era , many kinds of organisms died out . This was a mass extinction , in which many types of living things became extinct at the same time . The mass extinction , known as the Permian extinction , affected both plants and animals on land and in the seas . Scientists do not know what I catastrophic event caused the mass extinction , but many kinds of organisms suddenly became extinct . As much as 90 percent of marine species may have died out . The Supercontinent Scientists hypothesize that I climate change resulting from continental drift may have caused the mass extinction at the end of the . During the Permian Period , about 260 million years ago , Earth continents moved together to form a great landmass . or supercontinent , called ( pan uh ) The tion of caused deserts to expand in the tropics . At the same time , sheets of ice covered land closer to the South Pole . Many organisms could not survive the new climate . After formed , it broke apart again . What was ?

Go For Continental Drift activity A Visit Web Code . Chapters 291 , 22 The Geologic Time Scale Sequencing Events Which organisms appear or fishes ?

Precambrian Era Time million years ago 544 million Cambrian Ordovician Devonian Carboniferous million million 43 million million Precambrian Time begins with the formation of Earth . The first living things fishes live In bacteria the seas . Early appeared in seas amphibians billion years ago . Algae and fungi evolved Land plants and animals that billion years ' animals evolve . have legs and ago . Animals The can breathe air . first appeared similar to 600 million years , clams . and ago . appear on land . appear .

Era million years ago Jurassic Cretaceous Tertiary million million million million million years years ago years ago years ago years ago ago to the present sapiens Creodont The first The first New groups of Mammals , dinosaurs animals , flowering . evolve . first plants appear . including the plants , and turtles and At the end of first monkeys insects crocodiles Large dinosaurs the period . a and apes , dominate land . appear . roam the mass extinction appear . Humans appear . Mammals first world . The first causes the Flowering Later in the appear . birds appear . disappearance plants become period , many . bearing trees Mammals of many the most large mammals , A and palmlike become more organisms , common kinds including trees dominate common and including the of plants . First mammoths , forests . varied . dinosaurs . grasses appear . become extinct .

FIGURE 23 Flying Reptile was a flying reptile that lived during the Jurassic Period . Like dinosaurs , flying reptiles became extinct at the end of the Cretaceous period . Comparing and Contrasting How is similar to the bird in Figure 24 ?

2540 The Era Millions of years by as your time machine travels . Watch a dinosaur ! You re observing an era that read about in books and seen in movies . The Triassic Period Some living things survived the mian mass extinction . These organisms became the main forms of life early in the Triassic Period ( try AS ik ) Plants and animals that survived included , insects , reptiles , and plants called conifers . Reptiles were so successful during the Era that this time is sometimes called the Age of Reptiles . About 225 million years ago , the first dinosaurs appeared . Mammals also first appeared during the Triassic Period . A mammal is a vertebrate that feeds its young milk . Mammals probably evolved from reptiles . The mammals of the Triassic Period were very small . The Jurassic Period During the Period ( RAS ik ) dinosaurs became the dominant animals on land . Scientists have several hundred different kinds of dinosaurs . Some were plant eaters , while others were meat eaters . ruled Earth for about 150 million years . One of the birds . called . appeared during the Period . The name Archaeopteryx means ancient winged Many paleontologists now think that birds evolved from dinosaurs . i What Is a mammal ?

FIGURE 24 Early Bird The Cretaceous Period Reptiles , including dinosaurs , were still the dominant vertebrates throughout the Cretaceous Period ( TAY ) Flying reptiles and birds competed for places in the sky . The hollow bones and feathers of birds made them better adapted to their environment than the reptiles , which became extinct during the Cretaceous Period . The Cretaceous Period also brought new forms of life . ing plants like the ones you see today evolved . Unlike the conifers , plants produce seeds that are inside a fruit . The fruit helps the seeds disperse . Another Mass Extinction Catastrophic , or destructive , events have changed the history of life on Earth . Catastrophic happenings can include volcanoes erupting or objects from space hitting Earth . At the close of the Cretaceous Period , about 65 million years ago , another mass extinction occurred . Some scientists hypothesize that this mass extinction , known as the ( extinction , occurred when from space struck Earth . This object may have been an asteroid . Asteroids are rocky masses that orbit the sun between Mars and . When the asteroid hit Earth , the impact threw huge amounts of dust and water vapor into the atmosphere . Many organisms on land and in the oceans died immediately . Dust and heavy clouds blocked sunlight around the world for years . Without sunlight , organisms habitats changed . Plants died , and eating animals starved . This mass extinction wiped out over half of all plant and animal groups . No dinosaurs survived . Not all scientists agree that an asteroid impact alone caused the mass extinction . Some scientists think that climate changes caused by increased volcanic activity were partly responsible . The artist of the illustration ( left ) has given Archaeopteryx colorful feathers . From a fossil ( right ) paleontologists tan tell that Archaeopteryx was about 30 centimeters long . had leathers and teeth , and also had claws on its wings . FIGURE 25 The End of the Dinosaurs Many scientists hypothesize that during the Cretaceous an asteroid hit Earth near the Yucatan Peninsula , Mexico .

Life and Times . Place these events in their correct order continental glaciers retreat first fish appear oldest fossils form human ancestors appear invertebrate explosion occurs dinosaurs become extinct forms . Draw a timeline and graph these dates 35 billion years ago 544 million years ago 400 million years ago 260 million years ago 65 million years ago million years ago years ago Choose a scale so the oldest date fits on the paper interpreting Data Match each event with the correct date on your timeline . How does the time since the dinosaurs became extinct compare with the time since the oldest fossil formed ?

The Era Your voyage through time continues on through the called the Age of Mammals . During the Era , mammals had a hard time competing with dinosaurs for food and places to live . The extinction of dinosaurs ated an opportunity for . During the Era , mammals evolved to live in many different on land , in water , and even in the air . The Tertiary Period During the Tertiary Period . mates were generally warm . in the oceans , marine mammals such as whales evolved . On land , plants , insects , and mammals . When grasses evolved , they provided food for grazing mammals . These were the ancestors of today cattle , deer , sheep , and other mammals . Some mammals and birds became very large . The Quaternary Period The mammals that had evolved during the Tertiary Period eventually faced a changing . Earth climate cooled , causing a series of ice ages during the Quaternary Period . Thick continental glaciers advanced and retreated over parts of Europe and North ica . Then , about years ago , climate began to warm . Over thousands of years , the continental glaciers melted , except in Greenland and Antarctica . FIGURE 26 Environment Large mammals roamed the parts of North America during the ice Ages of the Quaternary Period .

In the oceans , algae , coral . mollusks , and mammals thrived . Insects and birds shared the skies . On land . flowering plants and mammals such as bats . cats , dogs , cattle , and to name a common . The fossil record suggests that modern humans , or Homo sapiens , may have evolved as early as years ago . By about to years ago . humans had migrated around the world to every continent except Antarctica Your time machine has now arrived back in the present . You and all organisms on Earth are living in the Quaternary Period of the Era . Is this the end of evolution and the changing of Earth surface ?

No , these processes will as long as Earth exists . But you have to take your time machine into the future to see just what happens ! How did Earth climate change Checkpoint ) during the Quaternary Period ?

Section Assessment FIGURE 27 Ice Age Art An early ancestor of modern humans painted these beautiful images of animals in a cave in France more than years ago . I ) Writing . Reading Target Reading Skill Create Outlines Use your outline of this section to help answer the questions below . Reviewing Key Concepts a . Defining What is the geologic time scale ?

I ) Inferring What information did ( use to develop the geologic time scale ?

a . Reviewing did the earliest organisms appear on Earth ?

Relating Cause and Effect How did early photosynthetic organisms change atmosphere ?

a . Listing List the periods of the . Describing How did organisms change during the first period of the ?

Relating Cause and Effect What event do scientists think may have caused the mass extinction at the end of the ?

a . Reviewing Which group of animals was dominant during the Era ?

Inferring How was their small size helpful to the mammals of the ?

Developing Hypotheses Many scientists think that the asteroid impact at the end of the Cretaceous prevented plant growth for many years . Although many dinosaurs were plant eaters , some were meat eaters . Develop a hypothesis to explain why all dinosaurs became extinct . Identifying What term do scientists apply to the Era ?

Inferring What conditions allowed so many different kinds of to evolve during the Era ?

Writing in Science . one stop geologic Ira . Chapter 291 As Time Goes By . Problem How can you make a scale model of geologic time ?

Skills measuring . calculating , making models Materials worksheet with asterisks one ream of paper . Starting from this asterisk , circle the asterisk Procedure that represents how many years ago each event in Table A occurred . PART a A . Label each circled asterisk to indicate the . Copy Table A into your lab notebook . Figure event . these ' i . Obtain a ream of copy paper . There are ! the ' ha 500 sheets in a ream . If each sheet had . Obtain a worksheet with asterisks asterisks on it , there would be a total printed on it . Each asterisk represents one of million asterisks . Therefore , each ream year . The first asterisk at the top represents would represent million years . one year ago . I Table A Historic Events You are born . One of your parents is born . First space shuttle sent into space . World War ends . Civil War ends . Declaration of Independence is signed . Columbus crosses Atlantic Ocean . Leif visits North America . mo

PART Table . Copy Table into your lab notebook . mine how much paper in reams or sheets would be needed to represent the events in geologic time found in Table . Hint Recall that each ream represents million years . Measure the thickness of a ream of paper . Use this thickness to calculate how thick a stack of paper would need to be to represent how long ago each geologic event occurred . Hint Use a calculator to multiply the ness of the ream of paper by the number of reams . Enter your results in Table . Analyze and conclude . Measuring Measure the height of your room . How many reams of paper would you need to reach the ceiling ?

How many years would the height of the ceiling represent ?

Which geologic events listed in Table would fall on a ream of paper inside your classroom ?

Calculating At this scale , how many rooms would have to be stacked on top of each other to represent the age of Earth ?

The time when vertebrates appeared ?

Calculating How many times higher would the thickness of the stack be for the age of Earth than for the breakup of ?

Making Models on your model , how could you distinguish one era or period from another ?

How could you show when lar organisms evolved and when they became extinct ?

Communicating is the scale of your model practical ?

What would be the advantages and disadvantages of a model that fit geologic time on a timeline meter long ?

More to Explore This model represents geologic time as a straight line . can you think of other ways of representing geologic time graphically ?

Using colored pencils , draw your own version of the geologic time scale so that it fits on a single sheet of typing paper . Hint You could represent geologic time as a wheel . a ribbon , or a spiral . 0299 Chapter Study Guide Evidence from rocks shows that life has existed for billions of years vi ' BIG . haw Earth has changed over time . The Rock Cycle ( Key Concepts , The principle of uniformitarianism states that the geologic processes that operate today also operated in the past . Rocks are into three igneous , sedimentary , and metamorphic . Internal and surface forces produce a rock cycle that builds , destroys , and changes rocks . Key Terms geology erosion uniformitarianism igneous rock sedimentary rock metamorphic rock rock cycle magma lava ' The Relative Age of Rocks Key Concepts According to the law of superposition , in horizontal sedimentary rock layers , each higher layer is younger than the layers below it . To determine relative age , geologists also study , intrusions . faults . gaps in the geologic record , and inclusions . Index fossils indicate the relative ages of the rock layers in which they occur . Key Terms relative age absolute age law of superposition extrusion intrusion fault inclusion index fossil Radioactive Dating Key Concepts During radioactive decay . the atoms of one element break down to form atoms of another . Radioactive dating is used to determine the absolute age of rocks . Radioactive dating indicates that Earth is roughly billion years old . Key Terms atom element radioactive decay 3000 Movement of Earth Plates Key Concepts According to the theory of plate tectonics , Earth landmasses have changed position over time because they are part of plates that are slowly movi . As Earth plates moved , landmasses changed their locations . These changes have affected where different kinds of organisms , past and present , are located . Key Terms plate theory of plate tectonics continental drift The Geologic Time Scale Key Concepts , Scientists have found fossils of organisms in rocks that formed about billion years ago . These earliest life forms were probably similar to bacteria . Geologists use the geologic time scale to show the time span of Earth history . At the beginning of the Era , many different kinds of organisms evolved . At the close of the Era , about 65 million years ago , a mass extinction occurred . Scientists hypothesize that this mass extinction occurred when an object from space struck Earth . During the Era , mammals evolved to live in many environments . Key Terms geologic time scale era period invertebrate vertebrate amphibian reptile mass extinction mammal

Review and Assessment . i Visit Web Code ) Target Reading mi Outlining To help you review Section , copy 8105 the incomplete outline at the right . Complete the outline by adding and details . Be sure IL Plate Movement and Organisms to include key concepts and key terms . A . Separation of Organism Reviewing Key Terms Choose the letter of the best answer . Complete the following sentences so that . The type of rock that forms when an existing ' a ' he key rock is changed by pressure or other factors is The principle of states radioactive rock . that sedimentary rock . metamorphic rock . igneous rock . Unlike absolute age , the relative age of a rock indicates only . Radioactive decay is the process in . A gap in the geologic record formed when which sedimentary rocks cover an eroded surface is called a ( he theory of plate tectonics states intrusion . at 10 . A mass extinction is a catastrophic event because extrusion . The time it takes for half of a radioactive elements atoms to decay is a ( Sue Ce era . relative age to the Grand absolute a how ' Earth outer layer consists of pieces called fossils contain . eras . plates . faults . The geologic time scale is subdivided into A me relative ages . absolute ages . eras and periods . Chapter 301

Review and Assessment Checking Concepts 11 . How does igneous rock form ?

12 . Describe a process that could cause an unconformity . 13 . How would a scientist determine the absolute age of a fossil ?

14 . Use the theory of plate tectonics to explain why fossils of have been found on several different continents . 15 . What was Barth early atmosphere like ?

16 . How did Earth environments change from the Tertiary Period to the Quaternary Period ?

Explain . Thinking Critically 17 . Applying Concepts Trilobites are index fossils . Paleontologists find a trilobite fossil in a rock layer at the top of a hill in South America . Then they find the same kind of fossil in a rock layer at the bottom of a cliff in Africa . What could the paleontologists conclude about the two rock layers ?

18 . Problem Solving Which of the elements in the table below would be better to use in dating a fossil from Precambrian time ?

Explain . Radioactive Elements ( years ) 713 million 19 . Relating Cause and Effect When formed , the climate on Earth became drier . How was this climate change more favorable to reptiles than amphibians ?

20 . Making Judgments If you see a movie in which early humans giant dinosaurs , how would you judge the accuracy of that movie ?

Give reasons for your judgment . 302 Math Practice 21 . Percentage What percentage of a radioactive element will remain after ?

Applying Skills Use the diagram of rock layers below to answer Questions . 20 years old Sedimentary rock layers Intrusion Extrusion 22 . Inferring According to the Law of Superposition , which is the oldest layer of sedimentary rock ?

Which is the youngest ?

How do you know ?

23 . Measuring What method did a scientist use to determine the age of the intrusion and extrusion ?

24 . Interpreting Data What is the relative age of layer ?

Hint With what absolute ages can you compare it ?

25 . Interpreting Data What is the relative age of layer ?

Standards Investigation Performance Assessment You have completed your illustrations for the timeline and travel brochure . Now you are ready to present the story of the geologic time period you researched . Be sure to include the awesome sights people will see when they travel to this time period . Don forget to warn them of any dangers that await them . In your journal , reflect on what you have learned about Earth history .

cAi Standards Practice Choose the letter of the best answer . Which of the following best shows that slow geologic processes can have a major impact on Earth ?

A continental drift index fossils , a Use the diagram below and your knowledge of science to answer Question . The diagram shows part of the boundary between the plate and the North American plate . The arrows show the plates direction of movement . In 100 years , how is the North American plate likely to have moved along this boundary ?

A far to the northwest of the plate I slightly to the northwest of the plate far to the southeast of the plate slightly to the southeast of the plate . A geologist identical index fossils in a rock layer in the Grand Canyon in Arizona and in a rock layer in northern Utah , more than 675 kilometers away . What inference can she make about the ages of the two rock layers ?

A The rock layer in the Grand Canyon is older . The rock layer in Utah is older . The two rock layers are about the same age . no inferences Success it ?

Tracker at Use the diagram below and your knowledge of science to answer Question . According to the law of superposition , the youngest layer of rock in this diagram is A layer A . layer . Layer Layer . What should you use so that the geologic time scale covering Earth history can be drawn as a straight line on a poster board one meter high ?

A million years years years years . Dinosaurs most likely became extinct because A disease killed most of the dinosaurs . large mammals preyed on them and reduced dinosaur populations . the dinosaurs couldn obtain enough water to survive . an asteroid hit Earth , causing severe climate change . App BIG Idea . Describe two methods geologists use to determine the age of a rock . in your answer , be sure to mention igneous rock , sedimentary rock , the law of superposition , index fossils , radioactive decay , and . Chapters 9303

Chapter Genetics The Science of Heredity Organisms produced by sexual reproduction inherit half their DNA from each parent . The new combination of DNA determines an organism traits . What controls the inheritance of traits in organisms ?

What is probability , and how does it help explain the results of genetic crosses ?

What role do chromosomes play in inheritance ?

What forms the genetic code ?

Chapter Modern Genetics ' BIG Idea A person traits depend on which alleles are inherited from each What are some patterns of inheritance in humans ?

How do geneticists trace the inheritance of traits ?

What are three ways of producing organisms with desired traits ?

Chapter Changes Over Time ' BIG Idea Genetic variation and environmental factors have together resulted in the evolution of species . How does natural selection lead to evolution ?

What evidence supports the theory of evolution ?

What factors have contributed to the diversity of species ?

How does a branching tree diagram show evolutionary relationships ?

Chapter Earth History ' BIG Idea Evidence from rocks shows that life has existed for billions of years and how Earth has changed over time . How do geologists determine the relative age of rocks ?

How does the theory of plate tectonics explain the movement of Earth landmasses ?

What were the major events of the , and Eras ?

parent , how those alleles work together , and environmental factors .

In northern Alaska and Siberia , part of the ground remains frozen all year round . This frozen layer is called permafrost . Scientists have drilled into the permafrost and found the remains of plants and animals , including woolly mammoths . giant . and other large animals that became extinct around years ago . Scientists have been able to take DNA samples from these remains and compare the results to other living and extinct organisms . Evidence from this DNA may help scientists determine how changes in climate and the environment may have led to the extinction of these large mammals . Scientists can use dating to determine when some organisms lived in the past . These data help scientists learn whether or not the organisms lived in a region at the same time . What is the function of DNA ?

Chapter ) carrying genetic information from . How would climate change most likely lead to the extinction of a species ?

Chapter ) parents to offspring Colder temperatures cause all organisms converting genetic instructions into in an area to freeze . proteins . The species can not adapt to the new climate . Predators kill more prey in order to survive in the changed climate . The species becomes geographically isolated due to the climate change . What process makes useful for dating objects ?

Chapter ) sedimentation superposition radioactive decay plate tectonics controlling the process of meiosis producing chains of amino acids . What technique allows scientists to see if two individuals are related ?

Chapter ) genetic engineering selective breeding DNA fingerprinting squares . Summary Summarize how scientists determine the genetic and evolutionary relationships between individuals and between species . What types of evidence do they use to support their conclusions ?

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