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6-8 > Earth Science
Grade level: 6-8 Subject: Earth Science Duration: Two class periods
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Objectives
 



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Students will understand the following:
1. Earth is estimated to be 4.6 billion years old.
2. Certain major events have occurred during this period that are considered important milestones in Earth’s development.
3. Early Earth was very different from our planet as we know it today.
4. Earth has existed as we know it today for only a very short time, relative to the number of years since its origin.
Materials

For this lesson, you will need:
• Computer with Internet access
• Books and articles concerning the birth and development of the Earth
• Forty-six sheets of white paper
• Tape
• Markers
Procedures

1. Tell the students that they will be creating a time scale of Earth’s history. Introduce the following background information to the class:
  • Scientists estimate that Earth formed approximately 4.6 billion (4,600,000,000) years ago.
  • Our planet began as a lifeless sphere, surrounded by hydrogen and methane and devoid of water; it was nothing like the planet we call our home today.
  • Certain important events are considered milestones in Earth’s history.
2. Write the following chronology and major geologic events on the chalkboard, and have students record them:
  • 4.6 billion years ago: Earth was created.
  • 4.5 billion years ago: Earth’s moon was formed.
  • 3.8 billion years ago: Bacteria arose.
  • 3.6 billion years ago: A cooling process began on Earth.
  • 3.0 billion years ago: Clouds formed.
  • 2.0 billion years ago: Eukaryotic cells (single cells with a nucleus) evolved.
  • 0.5 billion year ago: Oxygen began to saturate the atmosphere.
Point out to students that the Earth’s atmosphere has contained oxygen for only the most recent 10 percent of our planet’s history. Announce that they are about to discover more surprising facts about Earth’s geologic history.
3. Invite students to use the materials you have provided to research the development of Earth so that they can answer the following questions about additional important milestones in Earth’s geologic history:
  • When did primordial oceans form?
  • When did plant life begin to appear on Earth?
  • When did animal life begin to appear in the oceans?
  • When did the first land animals evolve?
  • When did humanlike life appear on Earth?
4. Have students share their findings by adding to the list of geologic events on the chalkboard.
5. Have volunteers help you to tape the 46 sheets of paper around the room, explaining that each sheet represents 100 million years of Earth’s history. Students should use markers to label the sheets: “4.6 billion years ago,” “4.5 billion years ago,” and so on.
6. Have additional volunteers work to transfer onto the appropriate sheets of paper the list of geologic events that you and the class have developed. If possible, involve each student in creating the geologic time scale.
7. Discuss with students what the time scale they have created reveals:
  • Which time period shows the most developments?
  • For approximately what fraction of the Earth’s total history have animals existed?
  • What about human beings?
  • How much space would an average human life span cover on the scale?
8. Ask students if creating the time scale has made them think in any new ways about our planet or about the relative place of human history in the bigger scheme of geologic history.