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# 9.2: The Evolution of Multicellular Life

Difficulty Level: At Grade Created by: CK-12

## Lesson 9.2: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. Most of Earth’s history passed before multicellular life evolved.

_____ 2. Dinosaurs went extinct just 65 thousand years ago.

_____ 3. Continental drift caused intense volcanic activity.

_____ 4. The disaster called the Cambrian explosion resulted in a tremendous mass extinction.

_____ 5. Birds evolved from reptile ancestors.

_____ 6. The Permian extinction was the biggest mass extinction the world had ever seen.

_____ 7. Sexual reproduction resulted in less variety among offspring.

_____ 8. Sexual reproduction slowed the rate of evolution.

_____ 9. Homo sapiens are primates.

_____ 10. The supercontinent called Pangaea formed during the Permian Period, just under 300 million years ago.

_____ 11. By 2 billion years ago, the first multicellular organisms had evolved.

_____ 12. Birds and insects filled the niches left by the dinosaurs.

_____ 13. The Triassic Period was the golden age of dinosaurs.

_____ 14. The Jurassic Period ended with the extinction of the dinosaurs.

_____ 15. During one ice age, snow and ice completely covered the planet.

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

Setting the Stage: The Late Precambrian

The late Precambrian is the time from about 2 billion to half a billion years ago. During this long span of time, Earth experienced many dramatic geologic and climatic changes.

• Continents drifted. They collided to form a gigantic supercontinent and then broke up again and moved apart. Continental drift changed climates worldwide and caused intense volcanic activity.
• Carbon dioxide levels in the atmosphere rose and fell. This was due to volcanic activity and other factors. When the levels were high, they created a greenhouse effect. More heat was trapped on Earth’s surface, and the climate became warmer. When the levels were low, less heat was trapped and the planet cooled. Several times, cooling was severe enough to plunge Earth into an ice age. One ice age was so cold that snow and ice completely covered the planet.

Life During the Late Precambrian

The dramatic changes of the late Precambrian had a major impact on Earth’s life forms. Living things that could not adapt died out. They were replaced by organisms that evolved new adaptations. These adaptations included sexual reproduction, specialization of cells, and multicellularity.

• Sexual reproduction created much more variety among offspring. This increased the chances that at least some of them would survive when the environment changed. It also increased the speed at which evolution could occur.
• Some cells started to live together in colonies. In some colonies, cells started to specialize in doing different jobs. This made the cells more efficient as a colony than as individual cells.
• By 1 billion years ago, the first multicellular organisms had evolved. They may have developed from colonies of specialized cells. Their cells were so specialized they could no longer survive independently. However, together they were mighty. They formed an organism that was bigger, more efficient, and able to do much more than any single-celled organism ever could.

The Precambrian Extinction

At the close of the Precambrian 544 million years ago, a mass extinction occurred. In a mass extinction, many or even most species abruptly disappear from Earth. There have been five mass extinctions in Earth’s history. Many scientists think we are currently going through a sixth mass extinction. What caused the Precambrian mass extinction? A combination of climatic and geologic events was probably responsible. No matter what the cause, the extinction paved the way for a burst of new life during the following Paleozoic Era.

Questions

1. Name two major events of the late Precambrian.

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2. Name three major adaptations for life during the late Precambrian.

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3. Explain the major benefits of the evolution of sexual reproduction.

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4. How did the first multicellular organisms evolve? What were the benefits of being multicellular?

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5. What is a mass extinction?

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## Lesson 9.2: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

1. Which division of time during Earth's history came first?
1. The Paleozoic Era
2. The Cenozoic Era
3. The Late Precambrian
4. The Mesozoic Era
2. Which period was the “golden age of dinosaurs”?
1. the Triassic Period
2. the Jurassic Period
3. the Cretaceous Period
4. the Tyrannosaurus Period
3. Pangaea
1. is a supercontinent of all the major landmasses.
2. formed during the Mesozoic Era.
3. allowed dinosaurs to roam all over the planet.
4. all of the above
4. The Permian extinction probably
1. occurred because photosynthesis stopped and the planet cooled.
2. occurred at the beginning of the Mesozoic Era, allowing the dinosaurs to evolve.
3. killed most life on Earth except for small reptiles and mammals.
4. all of the above
5. The dinosaurs disappeared at the end of the
1. Triassic Period.
2. Jurassic Period.
3. Cretaceous Period.
4. Mesozoic Period.
6. Which of the following did not occur during the Carboniferous Period?
1. The first amphibians left the water to live on land, but they had to return to the water to reproduce.
2. Plants and animals evolved adaptations to dryness.
3. Widespread forests of huge plants left massive piles of carbon that eventually turned to coal.
4. The first reptiles evolved.
7. When the dinosaurs went extinct ____________ million years ago, the ____________ took over.
1. 65, reptiles
2. 65, mammals
3. 145, mammals
4. 65, birds
8. Which of the following is not true about the Jurassic Period?
1. The earliest birds evolved from reptile ancestors during this time.
2. The major groups of mammals evolved during this time.
3. Flowering plants appeared for the first time.
4. The period ended with the dramatic extinction of small lizards, an important food for the large dinosaurs.

## Lesson 9.2: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.

Definitions

_____ 1. when many or even most species abruptly disappear from Earth

_____ 2. the era of “old life”

_____ 3. the era of “middle life”

_____ 4. the era of “modern life”

_____ 5. Earth during the ice age of the late Precambrian

_____ 6. the biggest mass extinction the world had ever seen

_____ 7. adaptation that created much more variety among offspring

_____ 8. spectacular burst of new life that began the Palezoic Era

_____ 9. when first dinosaurs branched off from the reptiles

_____ 10. the golden age of dinosaurs

_____ 11. when dinosaurs reached their peak in size and distribution

Terms

a. Cambrian explosion

b. Cenozoic Era

c. Cretaceous Period

d. Jurassic Period

e. mass extinction

f. Mesozoic Era

g. Palezoic Era

h. Permian extinction

i. sexual reproduction

j. snowball Earth

k. Triassic Period

## Lesson 9.2: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. During the late Precambrian, continents drifted. They collided to form a gigantic ____________.

2. During the late Precambrian, sexual ____________ created much more variety among offspring.

3. During the late Precambrian, the first multicellular organisms had ____________.

4. In a ____________, many or even most species abruptly disappear from Earth.

5. The Paleozoic Era began with a spectacular burst of new life, called the Cambrian ____________.

6. The Paleozoic Era ended with the biggest mass extinction the world had ever seen, known as the Permian ____________.

7. The Mesozoic Era is known as the age of ____________.

8. During the Triassic Period, the first dinosaurs branched off from ____________.

9. Dinosaurs flourished during the ____________ period.

10. The Cretaceous Period ended with the dramatic extinction of the ____________.

11. The Cenozoic Era is known as the age of ____________.

12. The last ice age ended about ____________ years ago.

## Lesson 9.2: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Describe three major events of life that occurred during the “age of dinosaurs.”

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