Geologic Time 19

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LESSON 1Key Concept Builder

Geologic History and the Evolution of Life Key Concept How is evolution affected by environmental change?

Environmental conditions in Precambrian time supported the evolution of the first life-forms on Earth. Precambrian life then led to the evolution of new, more complex life-forms in the Cambrian period.

Directions: On the line before each statement, write T if the statement is true or F if the statement is false.

1. The earliest of all fossil evidence is in rocks that are about 1.5 billion years old.

2. The earliest life-forms were single-celled.

3. Some Precambrian life-forms were multicellular.

4. Scientists discovered that multicelluar organisms existed about 2 bya.

5. Scientists hypothesize that large, Precambrian, soft-bodied multicellular organisms still exist.

6. The Cambrian explosion occurred about 700 mya.

7. The Cambrian explosion is significant because this is when the first soft-tissued organisms evolved.

8. Organisms from the Cambrian period left behind more fossil record evidence than organisms from Precambrian time.

9. Organisms from the Cambrian period had anatomy that was much different from present-day animals.

10. Scientists hypothesize that some Cambrian period organisms are distant ancestors of present-day organisms.

11. Fossil records from the Archean eon show that single-celled organisms existed at this time.

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Geologic Time 9

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Geologic History and the Evolution of LifeDirections: Write the correct term in the boxes to the right of each definition. Then unscramble the letters from the shaded boxes to spell a ninth term.

eon epoch era extinct geographic isolation

land bridge mass extinction period scale

Content Vocabulary

1. dying out

2. connects continents that previously had been separated by water

3. occurs when a physical barrier separates a population from the rest of its species

4. a subdivision of an eon

5. the longest unit of geologic time

6. a series of marks or points at known intervals

7. event during which many species die

8. a subdivision of a period.

LESSON 1

9. When they are unscrambled, the letters in the shaded boxes spell

, which is a subdivision of an era.

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16 Geologic Time

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Key Concept Builder LESSON 1

Geologic History and the Evolution of LifeKey Concept How was the geologic time scale developed?

Directions: On each line, write the term from the word bank that correctly completes each sentence. Each term is used only once.

epochs eras fossils Mesozoic

Paleozoic periods Phanerozoic Triassic

Eons Eras Eras Periods

Phan

eroz

oic

Ceno

zoic

Mes

ozoi

cPa

leoz

oic

MesozoicTertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

QuaternaryCenozoic

Paleozoic

Precambrian

065.5251

542

2500

1. Divisions in the geologic time scale were developed based on differences

in the in different rock layers.

2. Eons, the longest unit of geologic time, are subdivided into

.

3. Periods are subdivided into

.

4. Jurassic and the Ordovician are examples

of geologic .

5. The Cretaceous period is part of the

era.

6. The Cambrian period is part of the

era.

7. The Mesozoic era includes the

period.

8. The eon includes the Quaternary period.

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Geologic Time 17

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LESSON 1Key Concept Builder

Geologic History and the Evolution of Life Key Concept What are some causes of mass extinctions?

Directions: Answer each question on the lines provided.

1. What do all organisms depend on for survival?

2. What is a mass extinction?

3. What are two examples of environmental events that have caused mass extinctions?

4. How does volcanic activity cause climate change?

5. What happens to organisms that do not adapt to environmental changes?

6. What do scientists hypothesize contributed to the mass extinction of dinosaurs?

7. How many significant mass extinctions have occurred in Earth’s history?

8. What happened as Earth moved from the Permian to the Triassic period?

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18 Geologic Time

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Key Concept Builder LESSON 1

Geologic History and the Evolution of Life Key Concept How is evolution affected by environmental change?

Directions: Complete this cause-and-effect chart by writing a main effect of each cause in the space provided.

The Effect of the Environment on Evolution

Cause Effect

Sudden environmental change occurs.

1.

Earth experiences mass extinctions.

2.

Catastrophic changes in the environment occur.

3.

Earth’s tectonic plates slowly moved.

4.

Earth’s tectonic plates separate and reunite.

5.

Sea levels drop. 6.

Land bridges form between continents.

7.

Organisms are able to move into new areas.

8.

Earth’s tectonic plates separate landmasses.

9.

Animals become geographically isolated.

10.

Some animal species are not able to adapt to changes.

11.

Some organisms become physically separated.

12.

Climate changes occur. 13.

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Geologic Time 13

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Geologic History and the Evolution of Life Directions: On the line before each definition, write the letter of the term that matches it correctly. Each term is used only once.

Content Practice A

1. a subdivision of periods on the geologic time scale

2. the time line of Earth’s past

3. is nearly 90 percent of Earth’s history

4. the largest unit of geologic time

5. Mass extinctions are caused by sudden changes in this.

6. the disappearance of many species within a short time period

7. Organisms are dependent on this for survival.

8. provides evidence of meteorite impact

9. blocks sunlight resulting in environmental changes

10. the change in species over time as organisms adapt to their environments

11. connects two continents that were once separated

12. separation of species due to a physical barrier

13. the earliest life-forms

14. the sudden evolution of new, complex life-forms

A. Cambrian explosion

B. environment

C. eon

D. epoch

E. evolution

F. fossil record

G. geographic isolation

H. geologic time scale

I. iridium

J. land bridge

K. mass extinction

L. Precambrian time

M. single-celled organisms

N. volcanic activity

LESSON 1

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