Name
Date
Class
Eras of Earth’s History
Inquiry Warm-Up, Dividing History?
In the Inquiry Warm-Up, you investigated criteria for constructing and dividing a time
scale. Using what you learned from that activity, answer the questions below.
1. COMPARE AND CONTRAST How are the two timelines constructed by
you and another student similar and how are they different?
2. COMMUNICATE Why do timelines not include details about the event
listed for each date?
3. SEQUENCE Take the events on your timeline and list them in order of
importance, instead of by dates. How does the order differ from your
timeline order by dates?
4. COMMUNICATE Which method of showing information, a timeline
or a list of key events, would you use to present a person’s history?
Explain.
139A
Name
Date
Eras of Earth’s History
What Happened in the Paleozoic Era?
1a. LIST What are the periods of the Paleozoic Era?
b. SEQUENCE Number the following organisms in order from earliest to
latest appearance.
amphibians
jawless fishes
trilobites
bony fishes
c. RELATE CAUSE AND EFFECT Name two possible causes of the mass
extinction at the end of the Paleozoic Era.
I get it! Now I know that the main events in the Paleozoic Era were
I need extra help with
139B
Class
Name
Date
Class
Eras of Earth’s History
What Happened in the Mesozoic Era?
I get it! Now I know that the main developments in the Mesozoic Era were
I need extra help with
What Happened in the Mesozoic Era?
2a. IDENTIFY (Grasses/Flowering plants) first spread widely in the
Cenozoic Era.
b. EXPLAIN What factors allowed new organisms to spread during the
Cenozoic Era?
c. ANSWER
How do scientists study Earth’s past? Use an example
from this chapter in your answer.
I get it! Now I know that important events in the Cenozoic Era included
I need extra help with
139C
Name
Date
Class
Eras of Earth’s History
On a separate sheet of paper, explain how several different life forms have developed on
Earth.
139D
Name
Date
Class
Eras of Earth’s History
Understanding Main Ideas
Fill in the blank with the correct era or period to complete each statement.
1. Until the
, only one-celled organisms lived
on land, but during this period, plants became abundant.
2. At the start of the
, many organisms
evolved with hard parts including shells and outer skeletons.
3. During the
widely on land.
animals began to spread
4. At the end of the
Earth died.
, most species of life on
5. Reptiles were so successful that the
often called the Age of Reptiles.
is
6. At the close of the
ago, a second mass extinction occurred.
, about 65 million years
7. The first dinosaurs appeared during the
.
8. During the
, mammals evolved to live in
many different environments—on land, in water, and even in the air.
9. The fossil record suggests that humans migrated to most continents during the
.
Building Vocabulary
Match each definition with its term by writing the letter of the correct term in the right
column on the line beside the definition in the left column.
10.
animal with a backbone
a. reptile
11.
animal without a backbone
b. mammal
12.
animal that evolved from lungfish
c. invertebrate
13.
animal with strong legs and eggs with thick shells
d. mass extinction
14.
an event in which many types of living things die out at once
e. amphibian
15.
animal that feeds its young with milk
f. vertebrate
139E
Name
Date
Class
Eras of Earth’s History
Read the passages below. Then answer the questions that follow on a separate sheet
of paper.
The End of an Era
What happened at the close of the Mesozoic Era to cause the extinction of dinosaurs and many other
types of organisms? There is more than one theory. Each uses evidence from fossils and from analysis of
rock layers.
Theory 1: An Asteroid Impact
About 65 million years ago, an asteroid about 10 kilometers in diameter collided with Earth. The
impact had the force of millions of atomic bombs. Sediment and particles of the asteroid blasted into
the atmosphere. A dust cloud blocked the sun for months or longer. Plants and other organisms that
performed photosynthesis died, and many animals that depended on those plants for food died, too.
Blocking the sun also dropped Earth’s temperature, changing the climate. Animals that couldn’t adapt
became extinct. Evidence for this theory includes the fossil record, which shows many organisms died
out suddenly at the end of the Cretaceous Period. Scientists also discovered an impact crater in the Gulf
of Mexico. Other evidence includes a thin layer of rock around Earth enriched with the rare element
iridium—65 million years old. Asteroids contain iridium.
Theory 2: Volcanic Eruptions
About 65 millions years ago, huge volcanic eruptions occurred on the Indian subcontinent of south
Asia. Movements of Earth’s continents caused these eruptions. Lava poured over a large area, equal
in size to about half of Europe. Volcanic dust spewed into the atmosphere, and dark clouds encircled
Earth. For months or longer, the volcanic dust blocked the sun’s energy from reaching Earth’s surface,
causing plants, and then animals, to die. Evidence for this theory includes a fossil record, which shows
many organisms died suddenly at the end of the Cretaceous Period. Geologists identified a huge area of
volcanic rock 65 million years old on the Indian subcontinent. Also a thin rock layer enriched with iridium
around Earth dates back 65 million years. Eruptions produce dust-containing iridium.
1.
2.
3.
4.
5.
What is the evidence for the asteroid-impact theory?
What is the evidence for the volcanic-eruptions theory?
In each theory, what causes the extinction of plants and animals?
What evidence would be needed to prove one of the theories true?
Which theory makes the most sense to you? Give reasons.
139F
Name
Date
Class
Eras of Earth’s History
If the statement is true, write true. If the statement is false, change the underlined word
or words to make the statement true.
1.
Near the end of Precambrian Time, single-celled organisms
were joined by more complex living things.
2.
A(n) vertebrate is an animal without a backbone.
3.
During the Silurian Period, plants and insects became abundant
on Earth’s land.
4.
5.
6.
A(n) amphibian is an animal that lives part of its life on land
and part of its life in water.
Reptiles are invertebrates that evolved from amphibians.
Between 299 and 250 million years ago, Earth’s continents
formed a vast landmass called Pangaea.
Fill in the blank to complete each statement.
7. A(n)
things die out at the same time.
occurs when many types of living
8. The Mesozoic Era is often called the Age of
success of these animals.
because of the
9. The Triassic Period saw the rise of
vertebrates that feed milk to their young.
, or warm-blooded
10. The geologic period in which we are living is called the
.
139G
Eras of Earth’s History
Answer Key
9. Quaternary Period
1. Answers will vary. Both students’ timelines
may show segments are divided into similar
periods, or that the timelines represent a
person in the same type of profession, such
as an athlete or scientist. They may show
different time sections and different types of
events that represent the person they chose.
10. f
11. c
12. e
13. a
14. d
15. b
1. Evidence includes the fossil record, which
2. Answers will vary. Sample: Timelines are
shows many organisms died out 65 million
years ago, an impact crater near the Yucatán
Peninsula, and a layer of rock around Earth that
is enriched with iridium.
outlines of events during certain periods of
time. Details about each event would make
the timeline too cumbersome.
3. Answers will vary. Students may show key
2. Evidence includes the fossil record, which shows
accomplishments that appear in a different
order from how they occurred in time.
many organisms died out 65 million years ago,
a huge area of volcanic rock on the Indian
subcontinent from 65 million years ago, and a
layer of rock around Earth that is enriched with
iridium.
4. Answers will vary. Students may choose a
timelines because it shows the order in time
that the events happened. Some students
may choose the event list to show the most
important items first.
3. In each theory, a dust cloud blocks the energy
from the sun from reaching Earth’s surface for
months or longer. This causes plants, which use
energy from the sun to make food, to die, and
then animals die.
For much of Earth’s history, the only form of life
was single-celled organisms. Finally invertebrates
and vertebrates developed. Plants, fishes,
amphibians, and reptiles followed. Mammals,
birds, and flowering plants evolved before human
beings developed on Earth.
4. Answers may vary. A typical answer might
suggest that there is no evidence that could
prove absolutely that one or the other of these
theories is true.
5. Answers may vary. A typical answer might
suggest that the asteroid theory makes more
sense because volcanic eruptions in recent times
have not caused similar extinctions.
1. Silurian Period
2. Paleozoic Era
3. Devonian Period
1. true
2. invertebrate
4. Permian Period
3. true
4. true
5. Mesozoic Era
5. vertebrates
6. true
6. Cretaceous Period
7. mass extinction
8. Reptiles
7. Triassic Period
9. mammals
8. Cenozoic Era
139H
10. Quaternary Period