Biology (Holt)

Before You Begin

About 4.5 billion years ago, Earth was a ball

of molten rock. As the surface cooled, a

rocky crust formed and water vapor in the

atmosphere condensed to form rain. By 3.9

billion years ago, oceans covered much of

the Earth’s surface. Rocks formed in these

oceans contain of bacterial cells that

lived about 3.5 billion years ago. The

shows a progression of life-forms and

contains evidence of many changes in Earth’s

surface and atmosphere.

In this lab, you will make a

showing the major events in Earth’s history

and in the history of life on Earth, such as

the evolution of new groups of organisms and

the mass extinctions. This timeline can be

used to study how living things have changed

over time.

1.Write a definition for each boldface term

in the paragraphs above.

2.Make a data table similar to the one

at right.

3.Based on the objectives for this lab, write

a question you would like to explore about

the history of life on Earth.

Procedure

PARTA:Making a Timeline

1.Make a mark every 20 cm along a 5 m

length of adding-machine tape. Label one

end of the tape “5 billion years ago” and

the other end “Today.” Write “20 cm =

200 million years” near the beginning of

your timeline.

2.Locate and label a point representing the

origin of Earth on your timeline. Use your

textbook as a reference. See the timeline at

the bottom of Section 2 and Section 3 of

this chapter. Also locate and label the 11

periods of the geologic time scale begin-

ning with the Cambrian period.

3.Using your textbook as a reference, mark

the following events on your timeline:

the first cyanobacteria appear; oxygen

enters the atmosphere; the five mass

extinctions; the first eukaryotes appear;

the first multicellular organisms appear;

the first vertebrates appear; the first plants,

timeline

record

fossil

fossils

Exploration Lab

Making a Timeline of Life on Earth

SKILLS

• Observing


• Inferring relationships


• Organizing data

OBJECTIVES

• Compareand contrastthe
  distinguishing characteristics
  of representative organisms
  of the six kingdoms.


• Organizethe appearance of
  life on Earth in a timeline.

272 CHAPTER 12History of Life on Earth

MATERIALS

• 5 m roll of adding-
  machine tape


• meterstick


• colored pens or pencils


• photographs or
  drawings of organisms
  from ancient Earth to
  present day

Organism Kingdom Characteristics/adaptation

for life on Earth

2A 2B 2C 8B 8C