Exploration Lab Making a Timeline of Life on Earth

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Exploration Lab

Making a Timeline of Life on Earth

SKILLS ? Observing ? Inferring relationships ? Organizing data

OBJECTIVES ? Compare and contrast the distinguishing characteristics of representative

organisms of the six kingdoms. ? Organize the appearance of life on Earth in a timeline.

MATERIALS ? adding-machine tape (5 m roll) ? meterstick ? colored pens or pencils ? photographs or drawings of organisms from ancient Earth to present day

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 Earth's surface. Rocks formed in these oceans contain fossils of bacterial cells that lived about 3.5 billion years ago. The fossil record 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 timeline 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. Use a separate sheet of paper.

2. Record your data in the data table provided. 3. Based on the objectives for this lab, write a question you would like to

explore about the history of life on Earth.

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

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Making a Timeline of Life on Earth continued

Procedure

PART A: 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. Also locate and label the periods of the geologic time scale.

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, fungi, and land animals appear; the first dinosaurs and mammals appear; the first flowering plants appear; the first humans appear.

4. Look at the photographs of organisms provided by your teacher. Identify the major characteristics of each organism. Record your observations in the data table below.

Organism

Data Table

Kingdom

Characteristics/adaptation for life on Earth

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Making a Timeline of Life on Earth continued

5. Lay out your timeline on the floor in your classroom. Place photographs (or drawings) of the organisms you examined on your timeline to show when they appeared on Earth.

6. Fold the timeline at the mark representing 4.8 billion years ago. This leaves 24 segments, each representing 200 million years on your timeline. Now you can think of each segment as 1 hour in a 24-hour day.

7. When you are finished, walk slowly along your timeline. Note the sequence of events in the history of life on Earth and the relative amount of time between each event.

PART B: CLEANUP AND DISPOSAL

8.

Dispose of paper scraps in the designated waste container.

9.

Clean up your work area and all lab equipment. Return lab

equipment to its proper place.

ANALYZE AND CONCLUDE 1. Analyzing Information Think of each segment of your timeline as 1 hour in a 24-hour day as you answer each of the following questions.

a. How long has life existed on Earth?

b. For what part of the day did only unicellular life-forms exist?

c. At what time of day did the first plants appear on Earth?

d. At what time of day did mammals appear on Earth?

2. Summarizing Information Identify the major developments in life-forms that have occurred over the last 3.5 billion years.

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

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Making a Timeline of Life on Earth continued

3. Inferring Relationships How do mass extinctions appear to be related to the appearance of new major groups of organisms?

4. Justifying Conclusions Cyanobacteria are thought to be responsible for adding oxygen to Earth's atmosphere. Use your timeline to justify this conclusion.

5. Calculating Determine the amount of time, as a percentage of the time that life has existed on Earth, that humans (Homo sapiens) have existed.

6. Further Inquiry Write a new question about the history of life on Earth that could be explored in another investigation.

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

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