Lesson 1 | Geologic History and the Evolution of Life



Name Date Class

LESSON 1

Geologic History and the Evolution of Life

Directions: 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 | |

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.

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

, which is a subdivision of an era.

Geologic Time 9

Name Date Class

LESSON 1

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.

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

Geologic Time 13

Name Date Class

LESSON 1

Geologic History and the Evolution of Life

Key Concept How is evolution affected by environmental change?

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.

Geologic Time 19

Name Date Class

LESSON 1

The Biggest Event in the History of Earth

When Earth was a scant 50 million

years old, an infant planet still forming

and still largely molten, it collided with an

object about the size that Mars is today.

Fragments of the object and much of

Earth’s crust were flung into space. Quickly,

this material assumed an orbit around

Earth. Eventually, this material coalesced,

or combined, to become our Moon. This is

the best accepted theory of how the Moon

formed, but there are several others.

The Fission Theory

The fission theory proposes that Earth

was once spinning very rapidly—fast

enough to throw some of its crust into

orbit, which then coalesced into the Moon.

However, lunar soil has been exposed to

more intense heat, or baking, than Earth

soil. Lunar soil is not as hydrated as Earth

soil, meaning there are fewer molecules of

water inside lunar rock. If the Moon were

made entirely from Earth’s crust, the rocks

would not be different in this way.

The Capture Theory

The capture theory proposes that the

Moon formed somewhere else and was

simply captured by Earth’s gravity as it

drifted by. Scientists are reluctant to

believe that the Moon just drifted by at the

right time, at the right angle, and at the

right speed for Earth’s gravitational field

to capture it. This theory also does not

explain why Moon rocks have experienced

more baking than Earth rocks.

The Condensation Theory

The condensation theory proposes

that the Moon and Earth coalesced at the

same time from the material in the solar

nebula that formed the solar system. If this

were true, the Moon would have the same

composition as Earth. But it doesn’t. This

theory also fails to explain the Moon rocks’

extra baking.

The Giant Impactor Theory

An impactor about the size of Mars

struck Earth at an oblique angle. This

glancing blow, rather than a direct hit,

vaporized the impactor and removed some

of Earth’s molten mantle. The cataclysmic

collision created such heat that the ejected

material flew into space like molten

fireworks. This extreme heat explains the

extra baking of Moon rocks. The glancing

blow also gave Earth its 24-hour days. The

Moon now orbits Earth in the same

direction as Earth’s rotation.

This impactor material and Earth’s

mantle were put in orbit around Earth, and

this material eventually formed the Moon.

The giant impactor theory is the best fit

with what is known today.

Applying Critical-Thinking Skills

Directions: Respond to each statement.

1. Develop an idea about how Earth’s history might have been different if the Moon had

not been present.

2. Describe what might have happened to early Earth if, instead of an oblique hit, it had

been delivered a direct hit from a Mars-sized object while Earth was still mostly molten.

20 Geologic Time

Name Date Class

LESSON 1

Time-Travel Trips

Ninety percent of Earth’s history had already happened before the beginning of the

Paleozoic era. That early time is the Precambrian era, from the formation of Earth 4.6 bya to

542 mya. This era is divided into three eons—the Hadean, the Archean, and the Proterozoic.

Each of these eons experienced distinguishing events, especially the Archean and the

Proterozoic.

Plan a Travel Brochure

Suppose you are a travel agent who specializes in time travel. One of the trips is a tour

of Precambrian time, and visitors get to briefly visit and observe Earth during each of the

Precambrian eons. Your tour promises visitors that they will see at least one thing that

distinguishes each eon.

Design and illustrate a folding, three-page brochure that promotes your time tour of the

Precambrian. Write a brief statement that describes what the visitors will see on the tour,

and illustrate each eon in color. Include your notes on the panels below.

| | | |

-----------------------

Content Vocabulary

Content Practice A

Key Concept Builder

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.

Enrichment

Challenge

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download