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12.2: Lesson 12.1: The Origin of Earth

Difficulty Level: At Grade Created by: CK-12
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Key Concepts

  • Formation of the solar system
  • Formation of Earth and the moon
  • Formation of the atmosphere and oceans

Lesson Objectives

  • Describe how the solar system formed more than 4 billion years ago.
  • Explain how Earth’s atmosphere has changed over time.
  • Explain how Earth’s oceans formed.

Lesson Vocabulary

  • atmosphere: sphere of gases that surround a planet such as Earth
  • nuclear fusion: nuclear reaction in which two atomic nuclei fuse, or join together, to create a larger nucleus and release a huge amount of energy
  • water vapor: water in the gaseous state

Teaching Strategies

Introducing the Lesson

Introduce the formation of the solar system with the Orion Nebula, which is forming new stars and solar systems today. You can project the NASA image of the Orion Nebula at the following URL. Ask students if they know what the image represents. Tell them it shows a great swirling cloud of gas and dust out of which stars and solar systems are forming. Explain that if they could travel back in time about 5 billion years, this is how our own solar system might look, as they will learn in this lesson.



Students can see how the solar system formed by watching the short National Geographic video clip at this URL: http://video.nationalgeographic.com/video/kids/science-space-kids/solar-system-101-kids/.


With the activity “Birth of the Earth” at the following URL, students can make a timeline of Earth history. From the project, students will learn Earth’s age, milestones in Earth’s development, and how early Earth differed from the planet we know today.


Differentiated Instruction

Work with students to make a flow chart that represents the sequence in which the following formed: the sun, Earth, the moon, Earth’s atmosphere, and Earth’s oceans.


Have one or more creative students write a short story about the “birth” of the moon. The story should be told from the point of view of someone who lived on Earth at the time the moon formed. Ask the students to read their story to the class.

Science Inquiry

In this FlexBook® lesson, students learn that Earth’s initial atmosphere lacked oxygen. Point out that Earth’s present atmosphere is about 20 percent oxygen. Challenge students to predict how oxygen was added to Earth’s atmosphere. (It was added by the process of photosynthesis after the first photosynthetic organisms evolved.) Accept all reasonable responses at this point, and then tell students they will learn where the oxygen came from when they read the next lesson.

Common Misconceptions

Misconceptions about Earth’s age are common. Students may think that scientists disagree about the age of Earth or that Earth is only thousands, not billions, of years old. Made sure students are aware that scientists agree Earth is nearly 4.6 billion years old and that this estimate of Earth’s age is based on multiple sources of data.

Reinforce and Review

Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Earth Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.

Lesson Review Questions

Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.

Lesson Quiz

Check students’ mastery of the lesson with Lesson 12.1 Quiz in CK-12 Earth Science for Middle School Quizzes and Tests.

Points to Consider

How did life on Earth originate?

  • [Life began in the oceans, perhaps more than once. It probably began with the formation of the first biological molecule, perhaps RNA. Eventually, the earliest cells evolved.]

What were early landmasses like?

  • [Billions of years ago, landmasses came together to form a single supercontinent, and then they broke apart again. This happened five times in Earth’s history. Because early Earth was very hot, there was a lot of plate tectonic activity, including volcanoes and earthquakes.]

What happened when large amounts of oxygen entered the atmosphere?

  • [When large amounts of oxygen entered the atmosphere after photosynthesis evolved, some of the oxygen became ozone. The ozone protected Earth from harmful radiation, which allowed complex life forms to evolve. However, the oxygen was toxic to many existing organisms, which went extinct as a result.]

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