geologic time teacher guide

Key Concepts in Science

GEOLOGIC TIME TEACHER GUIDE

© 2015 Sally Ride Science

Student handouts are at the back of the Teacher Guide.

Correlation to Standards ............................................................................................................................ 3-4

Sally Ride Science Teacher Guides ............................................................................................................... 5

Geologic Time: About the Book ...................................................................................................................... 6

Getting Started: In Your World ........................................................................................................................7Preview Geologic Time, read the introduction, and discuss key concepts.

Chapter 1: Geologic Time ............................................................................................................................ 8-9Model creating a personal science dictionary, read Chapter 1, and make a Venn diagram.Students: Chapter 1 handout

Chapter 2: Absolute Age Dating .............................................................................................................. 10-11Model asking questions as you read, read Chapter 2, and discuss key concepts in the chapter.Students: Chapter 2 handout

Create a Comic Strip ......................................................................................................................................12Draw a comic strip about two geologists using different methods to date rocks.Students: Create a Comic Strip handout

Thinking Like a Scientist ...............................................................................................................................13Read about the extinction of the dinosaurs and analyze rock layers that tell the story.Students: Thinking Like a Scientist handout

Chapter 3: Earth’s History .............................................................................................................................14Model summarizing with a concept map, read Chapter 3, and make a circle graph.Students: Chapter 3 handout

Science Writing ..............................................................................................................................................15Write about past mass extinctions and the possibility of future mass extinctions.Students: Science Writing handout

How Do We Know?> Read How Do We Know? ........................................................................................................................16 Read about paleoecologist Karen Chin and answer the questions. Students: How Do We Know? handout

> Math Connection ..................................................................................................................................... 17 Calculate the amount of waste produced by dinosaurs based on their weight.

Students: Math Connection handout

Study Guide: Hey, I Know That! ............................................................................................................... 18-19Complete study guide questions.Students: Hey, I Know That! handout

GEOLOGIC TIME: CONTENTS

© 2015 Sally Ride Science 2

Correlation to Science StandardsFor information on alignment to state science standards and NGSS, visit https://sallyridescience.com/learning-products/product-standards

Correlation to Common CoreSally Ride Science’s Key Concepts and Cool Careers book series provide students with authentic literacy experiences aligned to Common Core in the areas of Reading (informational text), Writing, Speaking and Listening, and Language as outlined in Common Core State Standards for English Language Arts & Literacy in History/Social Studies, Science, and Technical Subjects. Geologic Time: Earth’s Remarkable Past and the accompanying activities align to the following standards:

Reading Standards for Literacy in Science and Technical Subjects 6-12 (RST)Grades 6-8

Key Ideas and Details1 Cite specific textual evidence to support analysis of science and technical texts.2. Determine the central ideas or conclusions of a text; provide an accurate summary of the text distinct from prior

knowledge or opinions.

Craft and Structure4. Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in

a specific scientific or technical context relevant to grades 6-8 texts and topics.

Integration of Knowledge and Ideas7. Integrate quantitative or technical information expressed in words in a text with a version of that information

expressed visually (e.g., in a flowchart, diagram, model, graph, or table).

Range of Reading and Level of Text Complexity10. By the end of grade 8, read and comprehend science/technical texts in the grades 6-8 text complexity band

independently and proficiently.

Writing Standards for Literacy in History/Social Studies, Science, and Technical Subjects 6–12 (WHST)Grades 6-8

Text Types and Purposes

1. Write arguments focused on discipline-specific content. a.-e.2. Write informative/explanatory texts, including the narration of historical events, scientific procedures/

experiments, or technical processes. b., d., f.

Production and Distribution of Writing4. Produce clear and coherent writing in which the development, organization, and style are appropriate to task,

purpose, and audience.

Research to Build and Present Knowledge7. Conduct short research projects to answer a question (including a self-generated question), drawing on several

sources and generating additional related, focused questions that allow for multiple avenues of exploration. 8. Gather relevant information from multiple print and digital sources, using search terms effectively; assess the

credibility and accuracy of each source; and quote or paraphrase the data and conclusions of others while avoiding plagiarism and following a standard format for citation.

9. Draw evidence from informational texts to support analysis, reflection, and research.

CORRELATION TO STANDARDS


Range of Writing10. Write routinely over extended time frames (time for reflection and revision) and shorter time frames (a single

sitting or a day or two) for a range of discipline-specific tasks, purposes, and audiences.

Speaking and Listening Standards 6-12 (SL)Grades 6-8

Comprehension and Collaboration1. Engage effectively in a range of collaborative discussions (one-on-one, in groups, and teacher-led) with diverse

partners on grade 6, grade 7, and grade 8 topics, texts, and issues, building on others’ ideas and expressing their own clearly. a.-d.

Presentation of Knowledge and Ideas4. Present claims and findings, sequencing ideas logically and using pertinent descriptions, facts, and details to

accentuate main ideas or themes; use appropriate eye contact, adequate volume, and clear pronunciation. Grade 6

Present claims and findings, emphasizing salient points in a focused, coherent manner with pertinent descriptions, facts, details, and examples; use appropriate eye contact, adequate volume, and clear pronunciation. Grade 7

Present claims and findings, emphasizing salient points in a focused, coherent manner with relevant evidence, sound valid reasoning, and well-chosen details; use appropriate eye contact, adequate volume, and clear pronunciation. Grade 8

Language Standards 6-12 (L)Grades 6-8

Vocabulary Acquisition and Use4. Determine or clarify the meaning of unknown and multiple-meaning words and phrases based on grade 6, grade

7, and grade 8 reading and content, choosing flexibly from a range of strategies. a.-d. 6. Acquire and use accurately grade-appropriate general academic and domain-specific words and phrases; gather

vocabulary knowledge when considering a word or phrase important to comprehension or expression.

CORRELATION TO STANDARDS


SALLY RIDE SCIENCE TEACHER GUIDES

The Sally Ride Science Key Concepts in Science and Cool Careers book series are available as print books and eBooks.* A Teacher Guide accompanies each of the 36 Key Concepts books and 12 Cool Careers books. More information: sallyridescience.com/learning-products

*Book pages pictured in the Teacher Guides are from eBook editions. Some pages in the print books have different images or layouts.

Sally Ride Science provides professional development and classroom tools to build students’ passion for STEM fields and careers. Founded by Dr. Sally Ride, America’s first woman in space, the company brings science to life for upper-elementary and middle school students.

Visit us at SALLYRIDESCIENCE.COM for more information.

Cool CareersCool Careers in BiotechnologyCool Careers in Earth Sciences Cool Careers in Engineering (Upper Elementary)Cool Careers in Engineering (Middle School)Cool Careers in Environmental Sciences (Upper Elementary)Cool Careers in Environmental Sciences (Middle School)

Cool Careers in Green ChemistryCool Careers in Information SciencesCool Careers in MathCool Careers in Medical Sciences Cool Careers in PhysicsCool Careers in Space Sciences

Key Concepts in ScienceAdaptations BiodiversityThe Biosphere Cells Earth’s Air Earth’s ClimateEarth’s Energy Earth’s Natural ResourcesEarth’s WaterElements and Compounds Energy BasicsEnergy Transformations

Flowering Plants Food Webs ForcesGenetics Geologic TimeGravityHeatLife Cycles LightMotion Organic Molecules Photosynthesis and Respiration

Physical Properties of Matter Plant and Animal Systems Plate Tectonics The Rock CycleSolids, Liquids, and Gases SoundSpace Exploration Sun, Earth, and MoonUnits of Measurement VertebratesThe Water CycleWeathering and Erosion


Geologic Time: Earth’s Remarkable Past uses real-world experiences to guide students to an understanding of our planet’s vast history. Students learn that Earth’s past spans 4.6 billion years. They discover how scientists use relative age dating, absolute age dating, and fossils to determine the ages and geologic history of rock layers. Students are introduced to the Geologic Time Scale, the special calendar that separates Earth’s long history into manageable time divisions based on important events, such as mass extinctions. At the end of each two-page spread, a brief statement called The Bottom Line reinforces students’ understanding by summing up the key ideas about geologic time covered in those pages.

In Your World engages students’ interest by challenging their ideas of what “old” means. The brief scenario takes students on a journey from the birth of our planet to the sound of people laughing some 4.6 billion years later. It gets students thinking about the vast history of Earth and the role geologists play in figuring out Earth’s past.

Chapter 1 introduces the Geologic Time Scale and methods of determining Earth’s age. Students learn about relative age dating and absolute age dating. The chapter also discusses how index fossils are used to determine the ages of rock layers.

Chapter 2 explores absolute age dating techniques in greater depth. Students learn that certain radioactive elements decay at predictable rates. By measuring how much of the original element is left in a rock, geologists can calculate the age of the rock.

Thinking Like a Scientist tells how some scientists used observations and analysis to conclude that a violent collision with an asteroid likely caused the extinction of dinosaurs and numerous other species around 65 million years ago. Students interpret and draw conclusions based on data similar to that used by scientists in the field.

Chapter 3 describes the major divisions of the Geologic Time Scale and explains that these divisions are based on important events in Earth’s past, such as mass extinctions and geologic catastrophes.

How Do We Know? focuses on Karen Chin, a paleoecologist who studies coprolites—rare chunks of fossilized dung—to interpret dinosaur food webs and other information about these extinct animals. Then, in Math Connection, students apply what they’ve learned about coprolites to calculate how much waste different types of dinosaurs generated each day.

Hey, I Know That! allows students to assess their own learning through a variety of assessment tasks related to the key concepts covered in Geologic Time.

GEOLOGIC TIME: Earth’s Remarkable Past About the Book


Preview the book

Before students begin reading Geologic Time, encourage them to scan the book. Read aloud the chapter titles in the table of contents. Tell students to look at the captions, labels, and visuals. Remind students that paying attention to these elements will help them to understand concepts in the text.

Read In Your World (pages 4 and 5) and discuss key concepts

Tell students to read In Your World. After they have finished reading, start a class discussion by asking,

How do you think geologists are like detectives? [Geologists try to solve mysteries about Earth’s past.]

What are some of the mysteries they try to solve? [They solve mysteries such as when extinct animals like trilobites lived, when flowers first bloomed, and how long ice ages lasted.]

What sorts of clues do geologists use to solve these mysteries? [Scientists use clues hidden in the rocks, such as fossils of plants or animals, to solves these mysteries.]

Call on several students to share their answers with the class. Tell students that as they read Geologic Time, they will learn about techniques geologists use in their detective work.

GEOLOGIC TIME: GETTING STARTEDIn Your World

Scientists use several methods—and sometimes a combination of methods—to determine the age of rocks. One method is relative age dating. Geologists assume that the bottom layer of rock is the oldest, the one above it is the next oldest, and so on. This method tells scientists which rocks are older but not what their actual ages are. Another method is absolute age dating. By seeing how much of the radioactive elements in rocks have decayed, or broken down into other substances, scientists can figure out when the rocks were formed. A third method is using index fossils. If the remains of a creature known to have lived during a certain period are found preserved in rock, scientists know the rock is from that period.

SCIENCE BACKGROUND


Read Chapter 1: Geologic Time

Before reading: Model creating a personal science dictionary

Tell students that learning science vocabulary can make understanding science concepts easier. Explain that you will model how they can create a personal science dictionary to help them learn science vocabulary.

Tell students that it’s helpful to write more than just a simple definition. Vocabulary entries could include descriptions, examples, sentences, and labeled diagrams. Begin by having students turn to page 7. Say,

I notice the term sedimentary rock. Do you know what it means?

Write sedimentary rock on the board. Then say,

Sometimes you can learn about the word by reading the sentences around it.

Call on a student to read aloud the second paragraph on page 7. Then say,

Hmm, so over time, bits of sediments get pressed into sedimentary rock. I’ll use that information to write a definition in my own words.

On the board, write Sedimentary rock is formed from bits of sand, rock, and seashells pressed together. Then have students look up the definition of sedimentary rock in the glossary. Say,

I’ll add the glossary definition under my definition.

On the board, write, Rock formed from the weathered pieces of other rocks that have been transported, deposited, compacted, and cemented. Then say,

I’ll also make a drawing to help me remember what sedimentary rock is.

Draw a quick diagram showing layers of rock. Then call on a couple of students to use sedimentary rock in a sentence. Write down their sentences. Tell students to copy all the information about sedimentary rock into their science notebooks. As they read Geologic Time, they can keep adding information about important words to create a personal science dictionary.

Read Chapter 1: Geologic Time (pages 6-13)

Ask students to read Chapter 1: Geologic Time. Give them the Chapter 1 handout and tell them to use it to take notes as they read. Point out that there is a space on the handout for them to draw pictures or diagrams for several of the important terms in Chapter 1.

After reading: Make a Venn diagram

Have pairs of students share their notes, discuss the main ideas of Chapter 1, and refine their notes if they wish. Then say,

What is the Geologic Time Scale? [The Geologic Time Scale is a special calendar that charts Earth’s long history.]

What are two methods that scientists use to determine the ages of rocks? [Relative age dating means figuring out which rock layer formed first, second, and so on. Absolute age dating determines the actual age of a rock in years.]

GEOLOGIC TIME: CHAPTER 1Geologic Time


Tell students they will work in pairs to make a Venn diagram that compares and contrasts relative age dating and absolute age dating.

Get students started by drawing two overlapping circles on the board. Label the left circle Relative age dating and the right circle Absolute age dating. Explain that in the overlapping section, students should list the characteristics that are shared by both kinds of dating. In the outer sections, they should list the characteristics that are peculiar to each kind of dating.

Tell student pairs to copy the Venn diagram and work together to fill it in. Then call on pairs to present their diagrams to the class. Discuss the diagrams and resolve any differences. [Examples of what to include in each section of the diagram:

Both—ways to determine the ages of rocks, methods used by geologists

Relative age dating—determines the order in which rock layers formed, works well with sedimentary rocks, uses index fossils to help determine the sequence of rock layers

Absolute age dating—determines how long ago rocks formed, works well with igneous or metamorphic rocks, uses changes in atoms to determine the age of rocks.]

GEOLOGIC TIME: CHAPTER 1Geologic Time


Read Chapter 2: Absolute Age Dating

Before reading: Model asking questions while you read

Begin by asking students to turn to page 14 in Geologic Time. Read aloud the title and subtitle of the chapter (Absolute Age Dating: Time Gets Real). Then tell students to look at the photograph of Mount Shasta on page 15 (pages 14 and 15 in the print book). Read aloud the caption: Mount Shasta, in Northern California, wassn’t built in a day. By dating Shasta’s rocks, geologists can trace a series of volcanic eruptions that formed different parts of the mountain over hundreds of thousands of years. Say,

That caption makes me wonder: How do geologists figure out when the volcanic eruptions that formed Mount Shasta occurred? I’ll write my question on the board.

On the board, write, How do scientists date rocks to figure out when volcanic eruptions happened? Call on a student to read the text on page 15. Then say,

Ah, this tells me that dating of rocks from volcanoes is based on the radioactive element potassium-40 and the fact that it decays at steady rate. But what if all the potassium-40 decays away? That’s another question, and I’ll look for the answer as I read.

Tell students that this is an example of asking questions while reading—an effective reading comprehension strategy.

Read Chapter 2: Absolute Age Dating (pages 14-17)

Ask students to read Chapter 2: Absolute Age Dating. Give them the Chapter 2 handout and tell them to use it to write down any questions that occur to them as they read. They can also use the handout to record any answers that they find. Note that the handout has a chart for them to complete about which radioactive elements could be used to date certain items.

ANSWER KEY FOR CHAPTER 1 HANDOUT[To date the oldest rocks on Earth, which are almost 4.3 billion years old, scientists used zircon because it decays very slowly and can be used to date really old rocks.To date volcanic rock from an eruption millions of years ago, scientists could use potassium-40, which has a half-life of 1.3 billion years.To date a mummy from ancient Egypt, scientists could use carbon-14, which has a half-life of 5,730 years.]

After reading: Discuss key concepts

Have students work in small groups. Ask each group member to share one question they still have about absolute age dating. Encourage group members to work together to find the answers in the text. Be sure to provide additional reference materials or valid science websites for students to use.

Then allow students to demonstrate their understanding of how radioactive elements are used for absolute age dating. On the board, make a chart showing the half-lives of these radioactive elements:

> Potassium-40 (half-life: 1.3 billion years)

> Uranium-238 (half-life: 4.5 billion years)

> Uranium-235 (half-life: 700 million years)

GEOLOGIC TIME: CHAPTER 2Absolute Age Dating


Ask students,

Which element would be most appropriate for dating rocks that are 100 million years old?

How about rocks that are 900 million years old?

Which would you use for rocks that are 2 billion years old?

Call on a student to answer each question, and then discuss the answers as a class until you come to an agreement on the best radioactive element to use in each case. [The best element to use in each case would have a longer half-life than the age of the rock, but its half-life would be relatively close to the age of the rock. So uranium-235 could be used to date a 100-million-year old rock, potassium-40 could date a 900-million-year old rock, and uranium-238 could date a 2-billion-year-old rock.]

GEOLOGIC TIME: CHAPTER 2Absolute Age Dating

A radioactive element is one that breaks down, or decays, spontaneously. When this happens, the element releases energy and particles and becomes another element. For example, over time, a sample of uranium-235 (U-235) will decay into lead-207 (Pb-207). The time it takes for half of an element to decay is called the element’s half-life. Because elements decay at steady rates, scientists can use half-lives to age date a substance. For instance, they can measure how much of the original U-235 in a rock has decayed and how much Pb-207 has been produced. Then they can backtrack to figure out when that rock formed.

SCIENCE BACKGROUND


Give students the Create a Comic Strip handout. It gives them a chance to demonstrate their understanding of relative age dating and absolute age dating by drawing a comic strip.

Relative and absolute age dating

Create a comic strip about two geologists, each using a different method to date rocks. Your comic strip should provide information about relative age dating and absolute age dating. Use captions or speech or thought balloons to explain what is happening in each panel.

GEOLOGIC TIMECreate a Comic Strip


Read Thinking Like a Scientist (pages 18-19) and answer the questions

Ask students to read Thinking Like a Scientist. Give them the Thinking Like a Scientist handout and tell them to use it to answer the questions on page 19. Encourage students to work in pairs to answer the questions. Have pairs share their answers with the class. If time permits, ask students to share the process they used to determine their answers.

Interpreting Data

Scientists sometimes use diagrams like the one here to present complex information in a way that is easy to understand. The diagram shows the rock layers that preserve the story of the dinosaurs all the way up to their extinction. You can see how events such as volcanic eruptions or an asteroid impact are written into the geologic record.

ANSWER KEY1. How do you think geologists determined when

dinosaurs lived in the first place? [Scientists figured out when dinosaurs lived by discovering which rock layers contained dinosaur fossils. Scientists used absolute age dating on the dateable material such as lava within or just above and below the layers of rocks containing dinosaur fossils.]

2. Which is the youngest layer shown in the diagram? The oldest? Why? [The upper layer is the youngest and the bottom layer is the oldest. Rocks usually are laid down layer after layer like a stack of books so the top layers are younger than the bottom layers. This principle is so important to scientists that it has a name—the law of superposition.]

3. Why are dinosaur fossils found below the iridium layer but not above it? [Dinosaurs went extinct just after an asteroid striking the Earth deposited the iridium layer. Since layers above the iridium were deposited after the asteroid strike, these deposits represent a time when dinosaurs no longer existed.]

4. Why is the layer containing iridium so thin? [This layer is thin because it was deposited over a relatively short time after the asteroid impact at Chicxulub in Mexico.]

GEOLOGIC TIME: THINKING LIKE A SCIENTISTAnalyze Rock Layers


Age of rocks (millions of years)

Tertiary age rocks

Jurassic age rocks

Jurassic age rocks

Cretaceous age rocks

1-centimeter-thick clay layer with iridium

Lava flow

20

65

145

206

Read Chapter 3: Earth’s History

Before reading: Model how to summarize with a concept map

Before students read Chapter 3: Earth’s History, give them the Chapter 3 handout. Point out that it has a place for them to summarize the chapter by making a concept map. To help students get started, draw a circle in the middle of the board and ask,

What is Chapter 3 about?

Listen to students’ responses and then write Earth’s History in the circle. Next, draw a second level of four or five circles, connecting them with lines to the first circle. Tell students that each level of the concept map provides more detail for the level above. Call on a student to read the caption on page 21 (page 20 in the print book). Then ask,

What are some important concepts about Earth’s history that we can write in the second level of our concept map?

Listen to students’ responses. In the second-level circles, write some of their answers, such as, Earth’s timeline goes from 4.5 billion years ago to today and Human beings are very recent newcomers.

Tell students to copy the concept map on their Chapter 3 handouts. Tell them they can add a third level of circles to give details about the concepts in the second level.

Read Chapter 3: Earth’s History (pages 20-25)

Ask students to read Chapter 3: Earth’s History. As they read, they should take notes on their handouts and add to their concept maps for Chapter 3. After students have finished reading, have them work in small groups to share their concept maps and discuss the key concepts in Chapter 3. Tell students they may refine their concept maps if they wish.

After reading: Make a circle graph

Have students look at the chart of the Geologic Time Scale on page 24. Tell them you want to make a circle graph showing the percentage of Earth’s past represented by Precambrian time and the other three major eras. Draw a circle on the board and ask,

About what percent of my circle should represent Precambrian time?

Listen to students’ responses. As a class, come to an understanding that the Precambrian time makes up about 88 percent of Earth’s geologic past. Draw a small wedge on your circle graph to represent the 12 percent of Earth’s history after Precambrian time. Then label the rest of the circle Precambrian time.

As a class, determine how to divide up the small slice of the circle graph representing the Paleozoic, Mesozoic, and Cenozoic eras. Then add those eras to your circle graph. [The Paleozoic era makes up 6.5 percent, the Mesozoic era makes up 4 percent, and the Cenozoic era makes up 1.5 percent.]

GEOLOGIC TIME: CHAPTER 3Earth’s History

Scientists rarely make scale representations of the Geologic Time Scale. This is because there are vast differences between the lengths of time of some periods and eras. The entire Geologic Time Scale spans over 4.6 billion years. To draw a scale representation would mean that Precambrian time would take up the vast majority of the scale, since that era spans nearly 4 billion years. By contrast, the Cenozoic era would take up only 1.5 percent of the scale, spanning 65 million years. This would make the Precambrian division over 60 times the size of the Cenozoic division! Instead of being divided proportionally by length of time, the Geologic Time Scale is divided into sections of variable sizes, based on the important events that took place during that era or period.

SCIENCE BACKGROUND


Give students the Science Writing handout. Students will use the handout to write two paragraphs: one about a past mass extinction and another about the possibility of future mass extinctions.

Write about mass extinctions

Several mass extinctions have occurred in Earth’s history. At the end of the Permian Period, for example, about 90 percent of all species disappeared. Scientists are not sure what causes every mass extinction, but they do know that several factors can contribute.

ANSWER KEY1. Write a paragraph describing how an environmental

change may have caused a mass extinction in Earth’s past. [Sample paragraph: An asteroid struck Earth 65 million years ago and caused a mass extinction. The asteroid killed off the dinosaurs and many other organisms. The impact killed a lot of living things right away. But many more plants and animals probably died in the days and years that followed because dust from the impact blocked sunlight from reaching Earth’s surface and drastically changed the global climate.]

2. Write a paragraph predicting whether mass extinctions might occur in Earth’s future. Use examples to support your answer. [Sample paragraph: Mass extinctions might occur in Earth’s future because conditions that cause mass extinctions could happen again. Scientists think that volcanoes and asteroids caused some of the mass extinctions in the past. Earth still has volcanoes, and an asteroid could hit our planet at some point. Also, human activities that destroy habitat and cause pollution and climate change might lead to mass extinctions.]

GEOLOGIC TIME Science Writing

An asteroid striking the Earth isn’t just the stuff of science fiction. Craters show that large asteroids have hit our planet throughout its long history, including the one that struck Earth 65 million years ago and killed off the dinosaurs. Scientists estimate that the asteroid was about 10 kilometers (6 miles) wide. But strikes by such huge asteroids are extremely rare. Smaller impacts are more common. If an asteroid the size of a house crashed into Earth, the energy of its impact would be similar to that of an atomic bomb. To figure out how a particular asteroid impact would affect Earth, you would need to know the size of the asteroid, its speed, the angle at which it hit Earth, and where it hit.

SCIENCE BACKGROUND


Read How Do We Know? (pages 26-29)

Give students the How Do We Know? handout for Geologic Time. Have them look at the questions on the handout for the first section, The Issue (page 26). Then have them read that section and answer the questions. Have them complete the rest of the sections (The Expert, page 27; In the Field, page 28; Technology, page 29) in the same way. Tell students to share their answers in pairs. Then go over each question as a class. Call on two or three students to share their answers to each question.

ANSWER KEY1. How did the science writer help you understand the topic? [Sample answer: The writer

defined terms that I didn’t know, such as coprolites.]

2. How did the science writer capture your interest? [Sample answer: The writer used descriptive phrases that helped me to picture the dinosaurs, such as “fearsome flesh-eaters.”]

3. What sparked Karen Chin’s interest in paleoecology? [She loved to go on camping trips to Yosemite with her family when she was little. She eventually became a park ranger there and learned all about dung.]

4. What are some of the tools that Karen uses in her work as a paleoecologist? [Karen uses a microscope in the lab to examine rare fossils up close. She uses a grinding machine to make thin sections of each coprolite before she puts it on a glass slide.]

5. How do people usually react when Karen tells them what she does for a living? How do their reactions change when she gives them additional information about her job? [People usually giggle when they first hear about Karen’s job. But then they think it’s interesting when she tells them that the specimens have turned to rock and explains all that she can learn by studying coprolites.]

GEOLOGIC TIME: HOW DO WE KNOW?Meet paleoecologist Karen Chin

Paleoecologists are scientists who study fossils in order to reconstruct ecosystems of the past. Paleoecology is a branch of paleontology—the study of ancient life. Both are branches of geology. Geologists study Earth, the rocky materials that make it up, the processes that shape it, and the ancient life forms that have lived on it, including how those life forms have changed over time. Most geologists specialize in fields such as paleontology, paleoecology, seismology (study of earthquakes), volcanology (study of volcanoes), petrology (study of rocks), and so on. Anthropology is the study of humans and their ancestors. Therefore, anthropologists study objects and environments that are much younger than those studied by geologists.

SCIENCE BACKGROUND


Answer the Math Connection questions (page 29)

Give students the Math Connection handout and have them use it to answer the Math Connection questions on page 29 of Geologic Time.

Math Connection: Waste TimeA 7,000-kilogram (15,400-pound) elephant can produce 100 kilograms (220 pounds) of droppings each day. Calculate the ratio of the elephant’s poop to its body weight. Then assume that this ratio is the same for each of the dinosaurs.

ANSWER KEYHow much—in kilograms and pounds—would each dino poop in a day?

Ratio of elephant’s weight to the weight of the droppings it produces each day: [The ratio is 70/1. (7,000 kg/100 kg (15,400 pounds/220 pounds) = 70/1)]

Therefore, the weight of droppings per day for each dinosaur would be:

Anchisaurus: [35 kg/70 (77 pounds/70) = 0.5 kg (1.1 pounds) droppings]

Barosaurus: [20,000 kg/70 (44,000 pounds/70) = 286 kg (629 pounds) droppings]

Gryposaurus: [2,000 kg/70 (4,400 pounds/70) = 29 kg (63 pounds) droppings]

Maiasaura: [3,500 kg/70 (7,700 pounds/70) = 50 kg (110 pounds) droppings]

Triceratops: [6,000 kg/70 (13,200 pounds/70) = 86 kg (189 pounds) droppings]

GEOLOGIC TIME: MATH CONNECTIONWaste Time


Complete the Hey, I Know That! study guide (page 30)

Give students the Hey, I Know That! handout and ask them to use it to answer the questions on page 30 of Geologic Time. Have pairs of students discuss their answers and note any disagreements they may have. Whip around the room, asking one student to read aloud a question and one or two students to share their answers to each question.

ANSWER KEY1. What is the law of superposition? Compare and contrast a stack of books to a sequence

of rock layers. (page 10) [The law of superposition is the assumption made by scientists that the layers of rock that are deepest were deposited first and so are the oldest, while the top layers were deposited most recently and so are the newest. While stacking books, the book you put down first would be on the bottom of the pile, while the book you put down last would be on the top of the pile. You can tell from the order of the books when they were put down, just as you can tell from the order of rock layers when they were deposited. However, the book on the bottom of the stack is not necessarily the oldest. But the bottom layer of rock is assumed to be the oldest.]

2. Imagine that you’ve been asked to date the items below. What methods would you use? What materials would you date? Keep in mind, there could be more than one right answer. (pages 8 and 9; pages 15 and 16)

a. A fish from before the Jurassic Period. [Sample answer: You could use index fossils found in the same rock layers with the fish fossils to discover when the fish lived.]

b. A mudslide that buried a forest within the last 1,000 years. [Sample answer: You could use carbon-14 dating to find the absolute age of the logs caught in the mud.]

c. Dinosaur footprints that occur just below a layer of lava. [Sample answers: You could use absolute age dating to find the age of the lava. Then relative age dating would tell you that the footprints are older than the lava.]

3. Look at these drawings of some fossils. Why do you think they make good index fossils? (pages 12 and 13) [Good index fossils generally come from organisms that lived only during a specific time. Each geologic period has special index fossils. For example, if you find a Perisphinctes tiziani fossil, the rock must be from the Jurassic period because that’s the only time this creature lived. Good index fossils also represent organisms that lived in many places around the world.]

4. A geologist estimates that when a particular rock formed, it contained 12 milligrams of radioactive potassium-40. The rock now contains 3 milligrams of potassium-40. The half-life of potassium-40 is 1.3 billion years. About how old is the rock? (pages 16 and 17) [The rock is about 2.6 billion years old. In its first half-life, the amount of radioactive potassium-40 decayed from 12 milligrams to 6 mg. Then, in its second half-life, the amount decayed from 6 mg to 3 mg. So, the potassium-40 in the rock has decayed for two half-lives, or 2.6 billion years.]

GEOLOGIC TIME: HEY, I KNOW THAT!Study Guide


Caption: Look at this drawing. In what order were the rock layers formed? Explain your reasoning. (pages 10 and 11) [Layer A is the oldest, because it is on the bottom. According to the law of superposition, the bottom layer of rock is assumed to be the oldest. Layer B is the next oldest, followed by Layer C and Layer D, because they were laid down in that order on top of the oldest layer. Layer E is the next oldest because it crosscuts the earlier layers but does not crosscut Layers F, G, or H. Then, following the law for superposition, Layer F is the next oldest, followed by Layer G. Layer H, the top layer, is the newest because it was laid down most recently.]

GEOLOGIC TIME: HEY, I KNOW THAT!Study Guide


STUDENT HANDOUTS

Key Concepts in Science

GEOLOGIC TIME


Geologic Time: Notes for Chapter 1As you read Chapter 1, write down the most important information you come across. Resist the urge to write down everything that you read. Instead, focus on the big ideas, or gist, of what you are reading.

THE GREAT PUZZLE__________________________________________________________________________________________

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WORLD’S LONGEST CALENDAR__________________________________________________________________________________________

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AGE-OLD QUESTIONS__________________________________________________________________________________________

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MIX AND MATCH__________________________________________________________________________________________

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LAYER-CAKE LOGIC__________________________________________________________________________________________

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PUZZLING IT OUT__________________________________________________________________________________________

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TALES FROM THE DEAD__________________________________________________________________________________________

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TIME INDEXED__________________________________________________________________________________________

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GEOLOGIC TIME • Chapter 1

PICTURE THISReview your notes for Chapter 1. Make drawings or diagrams to explain at least three of the vocabulary words in the chapter. Be sure to add labels and captions to your drawings.

PUT IT ALL TOGETHERUse your notes and drawings to help you identify and list the most important ideas—the key concepts—in Chapter 1.

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Absolute Age Dating: Notes for Chapter 2As you read Chapter 2, write down the most important information you come across. Resist the urge to write down everything that you read. Instead, focus on the big ideas, or gist, of what you are reading.

TIME GETS REAL__________________________________________________________________________________________

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RADIOMETRIC RECORDS

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GET A HALF-LIFE!__________________________________________________________________________________________

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BACKTRACK BOOGIE__________________________________________________________________________________________

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PICTURE THISSummarize Chapter 2 by completing the chart about how to date each item listed in the left-hand column. In the right-hand column, write down which radioactive element you could use to date each item and why it would be a good choice.

Half-lives of radioactive elements:

> Potassium-40 (half-life: 1.3 billion years)> Uranium-238 (half-life: 4.5 billion years)> Uranium-235 (half-life: 700 million years)

Item to be dated Which radioactive element would you use? Why?

The oldest rocks on Earth

Rock formed by a volcanic eruption millions of years ago

A mummy from ancient Egypt

PUT IT ALL TOGETHERUse your notes and chart to help you identify and list the most important ideas—the key concepts—in Chapter 2.

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__________________________________________________________________________________________© 2015 Sally Ride Science 2


Create a comic strip about two geologists, each using a different method to date rocks. Your comic strip should provide information about relative age dating and absolute age dating. Use captions or speech or thought balloons to explain what is happening in each panel.

Title: ___________________________________________________

Create a Comic Strip: Relative and Absolute Age Dating

GEOLOGIC TIME • Create a Comic Strip


Thinking Like a Scientist: Analyze Rock LayersRead Thinking Like a Scientist on pages 18 and 19 of Geologic Time. Then use the information on those pages and in the diagram to answer the questions.

Interpreting Data

Scientists sometimes use diagrams like the one here to present complex information in a way that is easy to understand. The diagram shows the rock layers that preserve the story of the dinosaurs all the way up to their extinction. You can see how events such as volcanic eruptions or an asteroid impact are written into the geologic record.

1. How do you think geologists determined when dinosaurs lived in the first place?

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2. Which is the youngest layer shown in the diagram? The oldest? Why?

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3. Why are dinosaur fossils found below the iridium layer but not above it?

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4. Why is the layer containing iridium so thin?

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GEOLOGIC TIME • Thinking Like a Scientist


Age of rocks (millions of years)

Tertiary age rocks

Jurassic age rocks

Jurassic age rocks

Cretaceous age rocks

1-centimeter-thick clay layer with iridium

Lava flow

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65

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Earth’s History: Notes for Chapter 3As you read Chapter 3, write down the most important information you come across. Resist the urge to write down everything that you read. Instead, focus on the big ideas, or gist, of what you are reading.

LIFE’S UPS AND DOWNS__________________________________________________________________________________________

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FROZEN IN TIME__________________________________________________________________________________________

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AN EXPLOSION OF LIFE__________________________________________________________________________________________

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CATASTROPHES HAPPEN__________________________________________________________________________________________

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NEVER-ENDING STORY__________________________________________________________________________________________

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PICTURE THISReview your notes for Chapter 3. Summarize your notes by developing a concept map that makes sense to you. You might start with a central circle labeled Earth’s History. Extending from this circle might be other circles describing different eras and periods in Earth’s history and important events that took place in each.

PUT IT ALL TOGETHERUse your notes and concept map to help you identify and list the most important ideas—the key concepts—in Chapter 3.

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Science Writing: Write About Mass ExtinctionsSeveral mass extinctions have occurred in Earth’s history. At the end of the Permian Period, for example, about 90 percent of all species disappeared. Scientists are not sure what causes every mass extinction, but they do know that several factors can contribute.

1. Write a paragraph describing how an environmental change may have caused a mass extinction in Earth’s past.

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2. Write a paragraph predicting whether mass extinctions might occur in Earth’s future. Use examples to support your answer.

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GEOLOGIC TIME • Science Writing

Review the questions below for each section of How Do We Know? Then read each section in the book and answer the questions.

THE ISSUE1. How did the science writer help you understand the topic?

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2. How did the science writer capture your interest?

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THE EXPERT3. What sparked Karen Chin’s interest in paleoecology?

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IN THE FIELD4. What are some of the tools that Karen uses in her work as a paleoecologist?

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TECHNOLOGY5. How do people usually react when Karen tells them what she does for a living? How do their reactions change when

she gives them additional information about her job?

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How Do We Know? What Dinosaurs Left Behind


GEOLOGIC TIME • How Do We Know?

Math Connection: Waste TimeA 7,000-kilogram (15,400-pound) elephant can produce 100 kilograms (220 pounds) of droppings each day. Calculate the ratio of the elephant’s poop to its body weight. Then assume that this ratio is the same for each of the dinosaurs.

How much—in kilograms and pounds—would each dino poop in a day?

Show your work for each calculation.

Ratio of elephant’s weight to the weight of the droppings it produces each day:

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Therefore, the weight of droppings per day for each dinosaur would be:

Anchisaurus: ______________________________________________________________________________

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Barosaurus: _______________________________________________________________________________

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Gryposaurus: ______________________________________________________________________________

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Maiasaura: ________________________________________________________________________________

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GEOLOGIC TIME • Math Connection

Use this sheet to answer the Hey, I Know That! questions on page 30 of Geologic Time.

1. What is the law of superposition? Compare and contrast a stack of books to a sequence of rock layers. (page 10)

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2. Imagine that you’ve been asked to date the items below. What methods would you use? What materials would you date? Keep in mind, there could be more than one right answer. (pages 8 and 9; pages 15 and 16)

a. A fish from before the Jurassic Period.

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b. A mudslide that buried a forest within the last 1,000 years.

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c. Dinosaur footprints that occur just below a layer of lava.

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3. Look at these drawings of some fossils. Why do you think they make good index fossils? (pages 12 and 13)

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Hey, I Know That! Study Guide

GEOLOGIC TIME • Hey, I Know That!


4. A geologist estimates that when a particular rock formed, it contained 12 milligrams of radioactive potassium-40. The rock now contains 3 milligrams of potassium-40. The half-life of potassium-40 is 1.3 billion years. About how old is the rock? (pages 16 and 17)

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Caption: Look at this drawing. In what order were the rock layers formed? Explain your reasoning. (pages 10 and 11)

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GEOLOGIC TIME • Hey, I Know That!


geologic time teacher guide

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