earth's history in geologic time.doc

Earth’s History in Geologic TimeGroup 2B

Dan Cyre, Robert Daub, Beth Lang

Introduction

This unit addresses two essential understandings:1) Geologic time is not uniform.2) Earth’s history is preserved in rock.

In an effort to develop the essential understanding, this unit asks students to answer one essential question: How is the Earth different today than in the past?Through the process of scientific inquiry and use of the modeling approach, the students will develop an understanding of how geological time is used to understand Earth’s past.

Standards

GR5-7 4.2.1 – understands that earth processes observed today (including movement of lithospheric plates and changes in atmospheric conditions) are similar to those that occurred in the past; earth history is also influenced by occasional catastrophes, such as the impact of a comet or asteroid

GR8-12 4.2.1 – understands geological time is used to understand the earth’s past

Background Knowledge Needed

There are certain science concepts that will be reinforced during this unit. In order to understand how Earth’s history is stored in rock, students should have a working knowledge of the three classes of rock: igneous, sedimentary, and metamorphic. They should also have an understanding of how fossils form. A unit on plate tectonics and continental drift will have been taught prior to the teaching of this unit. Some knowledge of Earth’s atmosphere and the carbon dioxide – oxygen cycle will also be required.

©Physical Science with Mathematical Modeling Workshop 2006A NCLB-ITQ Professional Development Funded Program

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Sequence

a) Pre-testb) Essential Question Whiteboard Discussionc) Geologic Time Scale Activityd) Fossils Activitye) Fossils Worksheetf) Introduction to Relative and Absolute Datingg) Relative Dating Worksheeth) Unit Reviewi) Post-test

Suggested Time Line (for 50 minute class periods)

Day 1: Pre-test, Whiteboard Essential Question, Geologic Time Scale Activity Research

Day 2: Construct a time line for the Geologic Time Scale, Whiteboard Discussion, Earth Calendar

Day 3: Fossil Inquiry – samples, Interactive Fossil Museum, Fossils WorksheetDay 4: Fossils Whiteboard Discussion, Introduce Relative and Absolute Dating,

Relative Dating WorksheetDay 5: Relative Dating Whiteboard Discussion, Unit ReviewDay 6: Post-test

Unit Overview PowerPoint


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Name

Date Pd

Earth’s History in Geologic TimePre-Post Test

1) Magma that forces its way into rock and hardens is called a(n)a) extrusionb) unconformityc) faultd) intrusion

2) A petrified fossil forms when a) minerals seep into the empty space of a mold. b) minerals replace all or part of an organism. c) an organism becomes trapped in amber. d) the weight of sediment squeezes everything away except carbon.

3) The earliest forms of life appeared during a) the Paleozoic Era. b) the Cenozoic Era. c) Precambrian Time. d) the Mesozoic Era.

4) On the Geologic Time Scale, eras are divided into a) epochs. b) indexes. c) periods. d) relative dates.

5) Fossils provide evidence for all of the following except for:

a) changes in the Earth’s surfaceb) how Earth originally formed.c) how environments on Earth have changed over

time. d) how groups of organisms have changed over time.

6) A part of the Mesozoic Era, named for the Jura Mountains in France, is a) Cenozoic Era b) Carboniferous Period c) Paleozoic Era d) Jurassic Period


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7) Most fossils form when organisms die and are buried in a) sediment b) faults c) unconformities d) ice

8) The Mesozoic Era is often called the a) Age of Mammals b) Age of Fish c) Age of Reptiles d) Age of Amphibians

9) Scientists use radioactive dating to a) determine the absolute ages of rocks. b) discover the source of index fossils. c) determine the relative ages of extrusions. d) find trace fossils in igneous rock.

FILL IN THE LINE TO CORRECTLY COMPLETE EACH STATEMENT. 10) A scientist who studies fossils is called a(n) _______________.

11) The process by which all living things have changed over long periods of time is called _____________.

12)The ____________ of a radioactive element is the time it takes for half of the radioactive atoms to decay.

13) Fossils are almost always found in ___________rock.

14) Plants and animals first reached land during the _____________Era.

15) An animal with a backbone is called a(n)_____________.

16) According to the law of superposition, the_________ layer is at the bottom. Each higher layer is_________ than the layers below it.

17) The ________ _____ is the number of years since the rock has formed.

18) The __________ _______ is the age of a rock compared to the ages of other rocks.

19) Is the following statement true or false? The deeper one travels into the Grand Canyon, the younger the rocks become. ___________

20) What is an unconformity?


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Name KEY

Date Pd


1)Magma that forces its way into rock and hardens is called a(n)a)extrusionb)unconformityc)faultd)intrusion





d) changes in the Earth’s surfacee) how Earth originally formed.f) how environments on Earth have changed over



7) Most fossils form when organisms die and are buried in©Physical Science with Mathematical Modeling Workshop 2006A NCLB-ITQ Professional Development Funded Program

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a) sediment b) faults c) unconformities d) ice



FILL IN THE LINE TO CORRECTLY COMPLETE EACH STATEMENT. 10) A scientist who studies fossils is called a(n) __paleontologist_________.

11) The process by which all living things have changed over long periods of time is called _evolution______.

12)The _half-life____ of a radioactive element is the time it takes for half of the radioactive atoms to decay.

13) Fossils are almost always found in _sedimentary__rock.

14) Plants and animals first reached land during the __Paleozoic_______Era.

15) An animal with a backbone is called a(n)_vertebrate_____.

16) According to the law of superposition, the_older___ layer is at the bottom. Each higher layer is_younger__ than the layers below it.

17) The _absolute_ _age__ is the number of years since the rock has formed.

18) The _relative____ __age___ is the age of a rock compared to the ages of other rocks.

19) Is the following statement true or false? The deeper one travels into the Grand Canyon, the younger the rocks become. __false_____

20) What is an unconformity? An unconformity is a gap in the geologic record. It shows where some rock layers have been lost to erosion.


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Earth’s History in Geologic TimeInquiry Activity – Bell Work

Essential Question:

How is Earth different today than in the past?

Teacher Notes:

Have the essential question on the board when the students come in.

Have the students brainstorm with their lab partner(s).

Have the students prepare a whiteboard presentation to answer the question.

Lead a whiteboard discussion in response to the essential question: “How is Earth different today than in the past?”


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Earth’s History in Geologic TimeInquiry Activity – Geologic Time Scale

Essential Understanding:Geologic time is not uniform.

Essential Question:How is Earth different today than in the past?

Materials:Geologic Time Scale handoutAdding machine tapePainter’s tapeMarking pensComputer with internet accessEarth Calendar handoutWhiteboards and markersMeter sticks

Procedure:1. Inform the students that they are going to work in small groups to create a time line of Earth’s history.

2. Give each student a copy of the Geologic Time Scale. The characteristics of each time period are left blank.

3. Instruct the student to use the internet web sites provided to research the Eras, Periods, and Epochs. Suggested web sites: http://serc.carleton.edu/NAGTWorkshops/visualization/collections/geotime.html

http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/gtpage9c.html As the students explore the suggested web sites, instruct them to complete the Geologic Time Scale by recording characteristics for each block of time.

4. Give each student a copy of the “What is a million” reading selection. Read and discuss the selection.


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http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/gtpage9c.html%0D

http://serc.carleton.edu/NAGTWorkshops/visualization/collections/geotime.html

5. Remind the students that each lab group will construct a time line to represent the Geologic Time Scale. Each group will need adding machine tape and markers, to construct the time line. 6. Before the students begin, reach a consensus as to an appropriate scale to use. A scale of 1 mm = 500,000 yrs will result in a time line that is 9.2 m in length.

7. Have the students cut off a piece of adding machine tape the appropriate length to represent 4.6 billion years, the age of Earth.

8. Have the students measure, mark and label each block of geologic time, beginning 4.6 billion years ago.

9. Have the students list characteristics for each block of time, on their time lines.

10. Next, have the students use painter’s tape to attach their time lines to the wall.

11. Assign specific blocks of geologic time to each group for a whiteboard presentation. Students should prepare a whiteboard presentation that highlights the major geological and biological events that occurred during their assigned portion of the time line.

12. Conduct a whiteboard discussion.

Discussion Topics:

1. Geologic time is not uniform.

2. Geological and biological events are used to separate the blocks of time. At the boundaries of each block of time you will find major changes in flora and fauna or major geologic events.

3. Life first appeared during Precambrian time. Fossils of bacteria have been found in Precambrian rocks. These early life forms added oxygen to the atmosphere and paved the way for more complex forms of life to evolve.

4. Eras are divided into periods, which are further divided into epochs.

5. The Jurassic Period was named after the Jura Mountains, in France. Dinosaur fossils were first studied in the Jura Mountains.


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6. The Mesozoic Era is sometimes called the Age of Reptiles, because of the prevalence of dinosaurs during that time.

7. Plants and animals first appeared on land during the Paleozoic Era.

8. The first vertebrates appeared during the Ordovician Period. Vertebrates are animals with a backbone.

Extension:

Give the students a copy of the Earth Calendar handout.

In the handout, major event in Earth history are listed with ages in millions of years before present. These ages are related to a corresponding calendar date. The calendar date is determined by setting midnight, January 1, to correspond with the formation of Earth. Midnight, December 31, corresponds with the present.

The purpose of this extension is to display Geologic Time in terms the students are familiar with. They can relate to a calendar year much easier than 4.6 billion years.

Assessment:

The extension activity described above may be used as a formative assessment tool, also.

Instead of giving the students a copy of the Earth Calendar, ask the students to apply their knowledge of Earth’s history to construct a one year calendar that corresponds to the Geologic Time Scale.


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Web Sites: Geologic Time Scale

Time Scale Link 1Time Scale Link 2

PowerPoint Link


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http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/gtpage9c.html

http://serc.carleton.edu/NAGTWorkshops/visualization/collections/geotime.html

Era Period EpochBegan

(millions of years)

Characteristics from geologic and fossil evidence

Cenozoic

QuaternaryHolocene 0.011

Pleistocene 1.8

Tertiary

Pliocene 5.3

Miocene 23.8

Oligocene 33.7

Eocene 54.8

Paleocene 65

Mesozoic

Cretaceous 144

Jurassic 206

Triassic 248

Paleozoic

Permian 290

Carboniferous Pennsylvanian 323

Carboniferous Mississippian 354

Devonian 417

Silurian 443

Ordovician 490

Cambrian 540

Precambrian time4600

Adapted from Modern Earth Science, 2002, Holt, Rinehart and Winston

Era Period EpochBegan

(millionCharacteristics from geologic and fossil

evidence©Physical Science with Mathematical Modeling Workshop 2006A NCLB-ITQ Professional Development Funded Program

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s of years)

Cenozoic

QuaternaryHolocene 0.011

End of last ice age; complex human societies develop

Pleistocene 1.8Woolly mammoths, rhinos, and early humans appear

Tertiary

Pliocene 5.3 Large carnivores (bears, dogs, cats) appear

Miocene 23.8 Grazing herds abundant; raccoons, wolves appear

Oligocene 33.7 Deer, pigs, horses, camels, cats and dogs appear

Eocene 54.8Early horses, flying squirrels, bats, and whales appear

Paleocene 65 Age of mammals begins; lemuroids appear

Mesozoic

Cretaceous 144

First flowering plants appear; mass extinctions (including all dinosaurs) mark end of Mesozoic period

Jurassic 206

Dinosaurs are dominant life form; flying reptiles and first birds appear.

Triassic 248

Dinosaurs first appear; ammonites common; cycads and conifers abundant; first mammals appear

Paleozoic

Permian 290

Pangaea comes together; mass extinctions mark the end of the Paleozoic era.

Carboniferous Pennsylvanian 323

Giant cockroaches and dragonflies common; coal deposits form; first reptiles appear

Carboniferous Mississippian 354

Amphibians flourish; sea stars common in ocean; forests and swamps cover most of the land

Devonian 417

Age of fishes; first amphibians appear; giant horsetails, ferns and cone-bearing plants develop

Silurian 443

Echinoderms appear; eurypterids abundant; first land plants and animals appear

Ordovician 490

Brachiopods increase; trilobites decline; gaptolites flourish; first vertebrates (fishes) appear

Cambrian 540

Advanced forms of marine life and first invertebrates appear; trilobites and brachiopods common

Precambrian time4600

Formation of the earth; continental shields appear; fossils are rare; stromalites are most common

Adapted from Modern Earth Science, 2002, Holt, Rinehart and Winston


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What is a Million?You hear people use the number "one million" all of the time: "The jackpot is worth over a million dollars! " "About a million people live in Phoenix (or San Francisco, or Dallas, or Detroit, or Baltimore)." "I've told you a million times to make your bed!" "Who wants to be a millionaire?"

You hear "a million" so often that you may think you know how big a million is. But do you really? Have you really been told a million times to make your bed? Have you met everyone in San Francisco? Have you ever tried to count a million dollars one at a time? For that matter, have you ever just tried to count to a million? Ten thousand? Or even one thousand? Counting at a rate of one number every second, it takes about 15 minutes to count to one thousand.

How long would it take to count to a million? Well, counting once per second (easy at the start, but tough when you reach the hundred thousand mark), eight hours per day, seven days per week (no weekends off), it would take you a little over a month to count to one million!

http://www.cotf.edu/ete/modules/msese/earthsysflr/geo_activity2.html


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Earth’s History in Geologic TimeInquiry Activity - Earth’s History is Preserved in Rocks

Fossil Examination

Essential Understanding:Earth’s history is preserved in rock.

Essential Question:What can rocks tell us about earth’s history?

Materials:Fossil samplesComputer with internet accessFossils reading selectionFossils worksheetWhiteboards and markers

Part I:Procedure:

1. Have the students examine fossil samples.

2. As the students examine the fossil samples, lead a class discussion as to the type of organisms that the fossils represent and the conditions under which the fossils may have formed.

3. Have the students do further inquiry using the following web site:http://fossils.valdosta.edu/home_time.htmlThis is an interactive fossil museum.

4. As the students explore the interactive museum, have them look at the correlation of fossils and geologic features around the world. Have the students infer what those correlations tell us about Earth’s history.

Part 2:Procedure:

1. Have the students take turns reading the Fossil selection aloud.

2. As the students read, conduct class discussions of the science concepts, as they come up. Some of the key topics to look for are: how most


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http://fossils.valdosta.edu/home_time.html

fossils form, in what type of rock does most fossils form, types of fossils, evolution, extinct, and paleontologists.

3. Have the students complete the Fossils worksheet.

4. Assign groups of worksheet questions to each lab group. Instruct students to prepare a whiteboard presentation for their questions.



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Name

Date Pd

Earth’s History in Geologic Time:Fossils Worksheet

Fossils are the preserved remains or traces of living things. Fossils provide evidence of how life has changed over time. Most fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shapes of the organisms. Scientists who study fossils are called paleontologists. They usually find fossils in sedimentary rock, the type of rock that is made of hardened sediment.

Most fossils form from animals or plants that once lived in or near quiet water such as swamps, lakes, or shallow seas. When an organism dies, generally only its hard parts leave fossils. Fossils found in rock include petrified fossils, molds and casts, carbon films, and trace fossils. Other fossils form when the remains of organisms are preserved in substances such as tar, amber, or ice.

Petrified fossils are fossils in which minerals replace all or part of an organism. The most common fossils are molds and casts. A mold is a hollow area in sediment in the shape of an organism or part of an organism. A mold forms when the hard part of an organism, such as a shell, is buried in sediment. Later, water carrying dissolved minerals may seep into the empty space of a mold. If the water deposits the minerals there, the result is a cast, a copy of the shape of the organism. Another type of fossil is a carbon film, an extremely thin coating of carbon on rock. Trace fossils provide evidence of the activities of ancient organisms. Fossil footprints, trails, and burrows are examples of trace fossils. Some processes preserve the remains of organisms with little or no change. Organisms can be preserved in tar, amber, or ice.

Paleontologists use the fossils they collect to determine what past life forms were like. Together, all the information that paleontologists have gathered about past life is called the fossil record. The fossil record provides evidence about the history of life on Earth. The fossil record also shows that groups of organisms have changed over time. It also reveals that fossils occur in a particular order, showing that life on Earth has evolved, or changed. Thus, the fossil record provides evidence to support the theory of evolution. A scientific theory is a well-tested concept that explains a wide range of observations. Evolution is the gradual change in living things over long periods of time. The fossil record shows that millions of types of organisms have evolved. Some have become extinct. A type of organism is extinct if it no longer exists and will never again exist.

Fossils provide evidence of Earth’s climate in the past. Paleontologists also use fossils to learn about past environments and changes in Earth’s surface.

Fill in the blanks in the table below.


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Type of Fossil Description1. Petrified fossil Fossils in which __________________ replace all or part of an

organism

2. A hollow area in sediment in the shape of an organism

3. A copy of the shape of an organism

4. Carbon film An extremely thin coating of ___________________ on rock

5. Trace fossils Evidence of the ________________ of ancient organisms

6. Remains of organisms in tar, amber, or ice

7. Describe how a mold is related to a cast.

8. What can a paleontologist tell from fossil footprints of a dinosaur?

9. What does the fossil record reveal about the evolution of life on Earth?

Fill in the blank to complete each statement.10. The process by which all the different kinds of living things have changed over long periods of

time is called ______________________.

11. The type of rock that is made of hardened sediment is called ___________________.

12. A type of organism is __________________ if it no longer exists and will never again live on Earth.

13. A(n) ______________________ is a scientist who studies fossils.

14. The preserved remains or traces of living things are called ____________________.

15. A well-tested concept the explains a wide range of observations is called a(n) __________________________.

From Science Explorer Earth Science, 2001


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Name KEY

Date Pd

Earth’s History in Geologic Time:Fossils Worksheet

Fossils are the preserved remains or traces of living things. Fossils provide evidence of how life has changed over time. Most fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shapes of the organisms. Scientists who study fossils are called paleontologists. They usually find fossils in sedimentary rock, the type of rock that is made of hardened sediment.

Most fossils form from animals or plants that once lived in or near quiet water such as swamps, lakes, or shallow seas. When an organism dies, generally only its hard parts leave fossils. Fossils found in rock include petrified fossils, molds and casts, carbon films, and trace fossils. Other fossils form when the remains of organisms are preserved in substances such as tar, amber, or ice.

Petrified fossils are fossils in which minerals replace all or part of an organism. The most common fossils are molds and casts. A mold is a hollow area in sediment in the shape of an organism or part of an organism. A mold forms when the hard part of an organism, such as a shell, is buried in sediment. Later, water carrying dissolved minerals may seep into the empty space of a mold. If the water deposits the minerals there, the result is a cast, a copy of the shape of the organism. Another type of fossil is a carbon film, an extremely thin coating of carbon on rock. Trace fossils provide evidence of the activities of ancient organisms. Fossil footprints, trails, and burrows are examples of trace fossils. Some processes preserve the remains of organisms with little or no change. Organisms can be preserved in tar, amber, or ice.

Paleontologists use the fossils they collect to determine what past life forms were like. Together, all the information that paleontologists have gathered about past life is called the fossil record. The fossil record provides evidence about the history of life on Earth. The fossil record also shows that groups of organisms have changed over time. It also reveals that fossils occur in a particular order, showing that life on Earth has evolved, or changed. Thus, the fossil record provides evidence to support the theory of evolution. A scientific theory is a well-tested concept that explains a wide range of observations. Evolution is the gradual change in living things over long periods of time. The fossil record shows that millions of types of organisms have evolved. Some have become extinct. A type of organism is extinct if it no longer exists and will never again exist.

Fossils provide evidence of Earth’s climate in the past. Paleontologists also use fossils to learn about past environments and changes in Earth’s surface.

Fill in the blanks in the table below.


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Type of Fossil Description1. Petrified fossil Fossils in which __minerals___________ replace all or part of an

organism

2. mold A hollow area in sediment in the shape of an organism

3. cast A copy of the shape of an organism

4. Carbon film An extremely thin coating of ___carbon____________ on rock

5. Trace fossils Evidence of the _activities__________ of ancient organisms

6. Preserved remains

Remains of organisms in tar, amber, or ice

7. Describe how a mold is related to a cast.A mold is an empty space in rock in the shape of an organism or part of an organism. If water carrying dissolved minerals and sediment seeps into the mold and deposits those minerals and sediments there, the result is a cast in the shape of the organism.

8. What can a paleontologist tell from fossil footprints of a dinosaur?Fossil footprints can provide clues about the dinosaur’s size and behavior.

9. What does the fossil record reveal about the evolution of life on Earth?The fossil record provides evidence that many different organisms have existed at different times. The fossil record also shows that groups of organisms have changed over time.

Fill in the blank to complete each statement.10. The process by which all the different kinds of living things have changed over long periods of

time is called ___evolution_______________.

11. The type of rock that is made of hardened sediment is called _sedimentary rock____.

12. A type of organism is ____extinct____________ if it no longer exists and will never again live on Earth.

13. A(n) __paleontologist_______________ is a scientist who studies fossils.

14. The preserved remains or traces of living things are called __fossils_____________.

15. A well-tested concept the explains a wide range of observations is called a(n) ___scientific theory_________________.



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Earth’s History in Geologic TimeEarth’s History is Preserved in Rocks

Relative and Absolute Dating Activities

Essential Understanding:Earth’s history is preserved in rock.

Essential Question:What can rocks tell us about earth’s history?

Materials: How Old is That Rock? - handout Relative Dating Reading selection – handout Relative Dating Worksheet Whiteboards and markers

Procedure:1. Have the students take turns reading the “How Old is That Rock?” handout.

2. Check for student understanding. Ask the students to give examples of relative age and absolute age.

3. Have the students take turns reading the Relative Dating selection.

4. As the students read, conduct class discussions of the science concepts, as they come up. Some of the key topics to look for are: relative age, absolute age, law of superposition, extrusion, intrusion, fault, unconformity, and index fossil.

5. Have the students complete the Relative Dating worksheet.

6. Assign groups of worksheet questions to each lab group. Instruct students to prepare a whiteboard presentation for their questions.



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How Old is That Rock?How can you tell the age of a rock or to which geologic time period it belongs? One way is to look at any fossils the rock may contain. If any of the fossils are unique to one of the geologic time periods, then the rock was formed during that particular time period. Another way is to use the "What's on top?" rule. When you find layers of rocks in a cliff or hillside, younger rocks are on top of older rocks.

But these two methods only give the relative age of rocks--which are younger and which are older. How do we find out how old a rock is in years? Or how do we know how long ago a particular group of fossilized creatures lived?

The age of a rock in years is called its absolute age. Geologists find absolute ages by measuring the amount of certain radioactive elements in the rock. When rocks are formed, small amounts of radioactive elements usually get included. As time passes, the "parent" radioactive elements change at a regular rate into non-radioactive "daughter" elements. Thus, the older a rock is, the larger the number of daughter elements and the smaller the number of parent elements are found in the rock. The time it takes for a radioactive element to change one-half of its radioactive parents into non radioactive daughters is called the half life of the element.

http://www.cotf.edu/ete/modules/msese/earthsysflr/ages.html


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Name

Date Pd

Earth’s History in Geologic Time: Finding the Relative Age of Rocks

The sediment that forms sedimentary rocks is deposited in flat layers. Over years, the sediment becomes deeply buried, hardens, and changes into sedimentary rock. At the same time, remains of organisms in the sediment may become fossils. These rock layers provide a record of Earth’s geologic history.

The relative age of a rock is its age compared to the ages of other rocks. The absolute age of a rock is the number of years since the rock formed. It can be difficult to determine the absolute age of a rock. Geologists use the law of superposition to determine the relative ages of sedimentary rock layers. According to the law of superposition, in horizontal sedimentary rock layers the oldest is at the bottom. Each higher layer is younger than the layer below it.

There are other clues to the relative ages of rocks. Geologists find some of these clues by studying extrusions and intrusions of igneous rock and faults. Igneous rock forms when magma or lava har5dens. Lava that hardens on the surface is called an extrusion. The rock layers below an extrusion are always older than the extrusion. 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.

More clues come from the study of faults. A fault is a break in Earth’s crust. A fault is always younger than the rock it cuts through. The surface where new rock layers meet a much older rock surface beneath them is called an unconformity. An unconformity is a gap in the geologic record. An unconformity shows where some rock layers have been lost because of erosion.

To date rock layers, geologists first give a relative age to a layer of rock at one location and then give the same age to matching layers 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 briefly. Index fossils are useful because they tell the relative ages of the rock layers in which they occur. Geologists use particular types of organisms, such as trilobites, as index fossils. Trilobites were a group of hard-shelled animals that evolved in shallow seas more than 500 million years ago. They later became extinct. Trilobite fossils have been found in many different places.


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Use the figure above to answer questions 1-4. 1. What is the youngest rock layer on the figure? Explain.

2. Is the extrusion older or younger than rock layer B? Explain.

3. Is the fault older or younger than rock layer A? Explain.

4. How could a geologist use the fossil in rock layer B to date a rock layer in another location?

Match each term with its definition by writing the letter of the correct definition on the line beside the term.

__________ 5. fault a. the number of years since a rock formed

__________ 6. extrusion b. a break or crack along which rocks move

__________ 7. unconformity c. the way to determine relative ages of rocks

__________ 8. relative age d. a hardened layer of magma

__________ 9. law of superposition e. the age of a rock compared with the age of otherrocks

__________10. intrusion f. fossils used to determine the relative ages of rock layers

__________11. absolute age g. a place where an eroded surface is in contact with a newer rock layer

__________12. index fossil h. a hardened layer of lava



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Name KEY

Date Pd

Earth’s History in Geologic Time: Finding the Relative Age of Rocks

The sediment that forms sedimentary rocks is deposited in flat layers. Over years, the sediment becomes deeply buried, hardens, and changes into sedimentary rock. At the same time, remains of organisms in the sediment may become fossils. These rock layers provide a record of Earth’s geologic history.

The relative age of a rock is its age compared to the ages of other rocks. The absolute age of a rock is the number of years since the rock formed. It can be difficult to determine the absolute age of a rock. Geologists use the law of superposition to determine the relative ages of sedimentary rock layers. According to the law of superposition, in horizontal sedimentary rock layers the oldest is at the bottom. Each higher layer is younger than the layer below it.

There are other clues to the relative ages of rocks. Geologists find some of these clues by studying extrusions and intrusions of igneous rock and faults. Igneous rock forms when magma or lava har5dens. Lava that hardens on the surface is called an extrusion. The rock layers below an extrusion are always older than the extrusion. 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.

More clues come from the study of faults. A fault is a break in Earth’s crust. A fault is always younger than the rock it cuts through. The surface where new rock layers meet a much older rock surface beneath them is called an unconformity. An unconformity is a gap in the geologic record. An unconformity shows where some rock layers have been lost because of erosion.

To date rock layers, geologists first give a relative age to a layer of rock at one location and then give the same age to matching layers 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 briefly. Index fossils are useful because they tell the relative ages of the rock layers in which they occur. Geologists use particular types of organisms, such as trilobites, as index fossils. Trilobites were a group of hard-shelled animals that evolved in shallow seas more than 500 million years ago. They later became extinct. Trilobite fossils have been found in many different places.


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Use the figure above to answer questions 1-4. 1. What is the youngest rock layer on the figure? Explain.

Rock Layer C—The law of superposition says the youngest rock is on top.2. Is the extrusion older or younger than rock layer B? Explain.

Younger—Extrusions are always younger than the rock layers below them.3. Is the fault older or younger than rock layer A? Explain.

Younger—A fault is always younger than the rock it cuts through. 4. How could a geologist use the fossil in rock layer B to date a rock layer in another location?

The fossil might be able to be used as an index fossil. Geologists can use index fossils to match up rock layers at locations that are far apart.

Match each term with its definition by writing the letter of the correct definition on the line beside the term.

_____b____ 5. fault a. the number of years since a rock formed

_____h____ 6. extrusion b. a break or crack along which rocks move

_____g____ 7. unconformity c. the way to determine relative ages of rocks

_____e____ 8. relative age d. a hardened layer of magma

_____c____ 9. law of superposition e. the age of a rock compared with the age of otherrocks

_____d____10. intrusion f. fossils used to determine the relative ages of rock layers

____a_____11. absolute age g. a place where an eroded surface is in contact with a newer rock layer


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____f_____12. index fossil h. a hardened layer of lava



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Name

Date Pd

Earth’s History in Geologic Time Review(designed to be used with a Classroom Performance System)

1. What is an unconformity?a. shows where some rock layers have been lost because of erosionb. shows where some rock layers have been lost because of extrusionc. break in the Earth’s crustd. lava that hardens on the Earth’s surface

2. Which of the following is a true statement based on the law of superposition?a. The youngest layer of rock is at the bottom.b. The higher the layer of rock, the older it is.c. The lower the layer of rock, the younger it is.d. The oldest layer of rock is at the bottom.

3. Which of the following is NOT an example of a vertebrate? a. plantb. fishc. humand. bird

4. During what era did land plants and animals emerge?a. Precambrianb. Paleozoicc. Mesozoicd. Cenozoic

5. What is evolution?a. when minerals seep into the empty spaces of a moldb. determining the absolute age of rocksc. process by which all living things have changed over timed. determining the relative ages of rocks using extrusions

6. A scientist who studies fossils is called…a. geologistb. biologistc. paleontologistd. therapist

7. What does radioactive dating show you?a. the relative age of rocksb. the absolute age of rocksc. the average age of rocksd. the scientific age of rocks

8. The Jurassic Period in the Mesozoic Era is named after the…©Physical Science with Mathematical Modeling Workshop 2006A NCLB-ITQ Professional Development Funded Program

31

a. Mesa Mountains in New Jerseyb. Jura Mountains in Francec. Jurassic Mountains in Italyd. Mesa Mountains in France

9. On the Geologic Time Scale, periods are the smaller segments ofa. epochsb. eras c. periodsd. eons

10. What forms when minerals replace all or part of an organism?a. petrified fossilb. organismc. castd. mold

TRUE/FALSE

11. Fossils show changes in the Earth’s surface.

12. Fossils show how environments have changed over time.

13. By studying fossils, paleontologists can see how organisms have changed over time.

14. The half-life of a radioactive element is the time it takes for the element to grow twice its size.

15. Fossils are usually found in igneous rock.

16. The absolute age of a rock is the number of years since the rock has formed.

17. The relative age of a rock is the number of years since the rock has formed.

18. The four eras on the Geologic Time Scale are Cenozoic, Mesozoic, Paleozoic, and Centerzoic.

19. Magma that hardens on the surface is called an extrusion.

20. Index fossils are useful because they tell the relative ages of the rock layers in which they occur.


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Name

Date Pd

Earth’s History in Geologic Time Review(designed to be used with a Classroom Performance System)

1. What is an unconformity?a. shows where some rock layers have been lost because of erosionb. shows where some rock layers have been lost because of extrusionc. break in the Earth’s crustd. lava that hardens on the Earth’s surface

2. Which of the following is a true statement based on the law of superposition?a. The youngest layer of rock is at the bottom.b. The higher the layer of rock, the older it is.c. The lower the layer of rock, the younger it is.d. The oldest layer of rock is at the bottom.

3. Which of the following is NOT an example of a vertebrate? a. plantb. fishc. humand. bird

4. During what era did land plants and animals emerge?a. Precambrianb. Paleozoicc. Mesozoicd. Cenozoic

5. What is evolution?a. when minerals seep into the empty spaces of a moldb. determining the absolute age of rocksc. process by which all living things have changed over timed. determining the relative ages of rocks using extrusions

6. A scientist who studies fossils is called…a. geologistb. biologistc. paleontologistd. therapist

7. What does radioactive dating show you?a. the relative age of rocksb. the absolute age of rocksc. the average age of rocksd. the scientific age of rocks

8. The Jurassic Period in the Mesozoic Era is named after the…©Physical Science with Mathematical Modeling Workshop 2006A NCLB-ITQ Professional Development Funded Program

33

a. Mesa Mountains in New Jerseyb. Jura Mountains in Francec. Jurassic Mountains in Italyd. Mesa Mountains in France

9. On the Geologic Time Scale, periods are the smaller segments ofa. epochsb. eras c. periodsd. eons

10. What forms when minerals replace all or part of an organism?a. petrified fossilb. organismc. castd. mold

TRUE/FALSE

11. Fossils show changes in the Earth’s surface. true

12. Fossils show how environments have changed over time. true

13. By studying fossils, paleontologists can see how organisms have changed over time. true

14. The half-life of a radioactive element is the time it takes for the element to grow twice its size. false

15. Fossils are usually found in igneous rock. false

16. The absolute age of a rock is the number of years since the rock has formed. true

17. The relative age of a rock is the number of years since the rock has formed. false

18. The four eras on the Geologic Time Scale are Cenozoic, Mesozoic, Paleozoic, and Centerzoic. false

19. Magma that hardens on the surface is called an extrusion. false

20. Index fossils are useful because they tell the relative ages of the rock layers in which they occur. true


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Name

Date Pd


1)Magma that forces its way into rock and hardens is called a(n) a) extrusion

b) unconformityc) faultd) intrusion





g) changes in the Earth’s surfaceh) how Earth originally formed.i) how environments on Earth have changed over




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7) Most fossils form when organisms die and are buried in a) sediment b) faults c) unconformities d) ice



FILL IN THE LINE TO CORRECTLY COMPLETE EACH STATEMENT. 10) A scientist who studies fossils is called a(n) _______________.

11) The process by which all living things have changed over long periods of time is called _____________.

12)The ____________ of a radioactive element is the time it takes for half of the radioactive atoms to decay.

13) Fossils are almost always found in ___________rock.

14) Plants and animals first reached land during the _____________Era.

15) An animal with a backbone is called a(n)_____________.

16) According to the law of superposition, the_________ layer is at the bottom. Each higher layer is_________ than the layers below it.

17) The ________ _____ is the number of years since the rock has formed.

18) The __________ _______ is the age of a rock compared to the ages of other rocks.

19) Is the following statement true or false? The deeper one travels into the Grand Canyon, the younger the rocks become. ___________

20) What is an unconformity?


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Name KEY

Date Pd


1)Magma that forces its way into rock and hardens is called a(n)a) extrusionb) unconformityc) faultd) intrusion





a. changes in the Earth’s surfaceb. how Earth originally formed.c. how environments on Earth have changed overtime.

d) how groups of organisms have changed over time.


7) Most fossils form when organisms die and are buried in©Physical Science with Mathematical Modeling Workshop 2006A NCLB-ITQ Professional Development Funded Program

37

a) sediment b) faults c) unconformities d) ice



FILL IN THE LINE TO CORRECTLY COMPLETE EACH STATEMENT. 10) A scientist who studies fossils is called a(n) __paleontologist_________.

11) The process by which all living things have changed over long periods of time is called _evolution______.

12)The _half-life____ of a radioactive element is the time it takes for half of the radioactive atoms to decay.

13) Fossils are almost always found in _sedimentary__rock.

14) Plants and animals first reached land during the __Paleozoic_______Era.

15) An animal with a backbone is called a(n)_vertebrate_____.

16) According to the law of superposition, the_older___ layer is at the bottom. Each higher layer is_younger__ than the layers below it.

17) The _absolute_ _age__ is the number of years since the rock has formed.

18) The _relative____ __age___ is the age of a rock compared to the ages of other rocks.

19) Is the following statement true or false? The deeper one travels into the Grand Canyon, the younger the rocks become. __false_____

20) What is an unconformity? An unconformity is a gap in the geologic record. It shows where some rock layers have been lost to erosion.


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earth's history in geologic time.doc

Documents

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