IAES Plate Tectonics: Activity 39 “Earth Time”
Absent Work
Key Words: Geological Time, Paleontologist
Getting Started:
1. Match the following events to the time it occurred by drawing a line to connect the two.
Event Years Ago
Extinction of 90% of marine life on earth
Thousands
The last Ice Age Millions
Age of oldest fossil Billions
The correct answer is at the bottom of this page. However, there is no reason to change your original answer because this question is meant to have you make a hypothesis.
2. By placing these events in order, you have created a chronological timeline. In this activity, you will do something similar. Scientists who study the history of the earth – known as paleontologists – refer to periods of thousands, millions, and billions of years as geological time.
3. Read the Introduction and Challenge to Activity 39, “Earth Time,” in your Student Book on page D-
20.
Procedure:
1. Imagine that your friend is studying to be a paleontologist. She asks you to help her list some events in the history of the earth in order. She’s interested in organizing her ideas into the four time periods shown on Student Sheet 39.1, “Ordering Events,” which is attached to this packet.
2. Cut out the “Event on Earth” cards that are attached to this packet. Carefully read the information on the front of each card.
3. Place each event in order, from oldest to most recent. Hint: If you need help, read the clue on the back of the card. Some clues will help you put the events in order, while other clues will help you identify the time period in which an event occurred.
4. On Student Sheet 39.1, “Ordering Events,” record the order of events that you have decided upon with your group. Be sure to place each event in the time period in which you think it occurred.
Answer to Getting Started #1: The last Ice Age happened thousands of years ago. There was a mass extinction of the earth’s marine life millions of years ago. The oldest fossil is billions of years old.

5. Your friend suddenly remembers that she wrote down the order of these events in her science notebook. Watch the video link below to view Student Sheet 39.2, “Paleontology Student’s Notes.” Use the information on Student Sheet 39.2 to rearrange the cards in the order scientists have determined from geologic evidence. Record the revised order on Student Sheet 39.1 in a different color ink so that your teacher may see your original hypothesis. http://www.youtube.com/watch?v=mpfC8gn8GBY
Analysis Questions:
1. How did your original order of events differ from that of paleontologists? Explain.
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2. Would units of time such as minutes and hours be useful in measuring events in earth’s history?
Why or why not?
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3. Some nuclear waste may be radioactive for 250,000 years. Would you consider this to be a long or short period in geological time? Explain your reasoning.
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4. Your younger brother tells you about a television show he watched where humans ride dinosaurs instead of cars. He says he wishes he could go back to the time when people lived with dinosaurs.
Based on what you learned in this activity, what do you tell him?
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5. Reflection: How did first placing these events in order yourself help you to understand Earth’s history? Hint: Think about how your understanding of events in geological time has changed.
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EVENTS ON EARTH
Earth formed
EVENTS ON EARTH
Fossil evidence of first life on earth
3
EVENTS ON EARTH
Fossil evidence of first land plants
5
EVENTS ON EARTH
Age of reptiles
1
7
EVENTS ON EARTH
Yucca Mountain formed
9
EVENTS ON EARTH
Oldest rock
EVENTS ON EARTH
Appalachian Mountains began to form
EVENTS ON EARTH
Fossil evidence of first reptiles
EVENTS ON EARTH
Dinosaurs became extinct
EVENTS ON EARTH
Fossil evidence of first modern humans
(Homo sapiens)
10
8
6
4
2

Clue:
The earth is 4.5 billion years old, and is older than almost anything on its surface.
1
Clue:
Some fossils of blue-green algae are almost 3.5 billion years old.
3
Clue:
Land plants evolved from green algae.
5
Clue:
Some rocks are older than any of the organisms that have lived on the earth.
2
Clue:
The mountain chain in the eastern United
States began to form before there were plants or reptiles on the earth.
4
Clue:
Fossils of one of the earliest-known reptiles suggest that it was a plant-eater.
6
Clue:
Dinosaurs were some of the largest reptiles during this age, which occurred 65-248 million years ago.
7
Clue:
Dinosaurs became extinct only after they lived on the earth.
8
Clue:
Yucca mountain formed from volcanic eruptions that occurred 11-14 million years ago.
9
Clue:
Two skulls found in Ethiopia, which is in Africa, are 195,000 years old.
10

Events on Earth:
Original Order
Ordering Events
Time Period
Events on Earth:
Revised Order
Less than 50 million years ago
50-250 million years ago
250-500 million years ago
Issues and Earth Science - Student Sheet 39.1
More than
500 million years ago