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12.1: The Origin of Earth

Difficulty Level: At Grade Created by: CK-12
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Lesson 12.1: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. The solar system formed from a giant mass of gas and dust.

_____ 2. The sun formed billions of years before other objects in the solar system.

_____ 3. The solar nebula formed a disk before it formed the sun.

_____ 4. Objects in our solar system include dwarf planets.

_____ 5. As Earth formed, gravity pulled lighter materials to the center of the planet.

_____ 6. Earth’s mantle is made entirely of liquid rock.

_____ 7. There was a lot of space debris in the early solar system.

_____ 8. Earth’s moon began as a dwarf planet orbiting the sun.

_____ 9. From the time it first formed, Earth has always had an atmosphere.

_____ 10. Some of the gases in Earth’s early atmosphere came from comets.

Lesson 12.1: Critical Reading

Name___________________ Class______________ Date________

Read this passage based on the text and answer the questions that follow.

How the Solar System Formed

Our solar system began to form about 5 billion years ago. The Sun, planets, and other solar system objects all formed at about the same time. They formed from a giant cloud of gas and dust called the solar nebula. The cloud pulled together and began to spin. As it contracted, its temperature and pressure increased. The cloud spun faster and formed into a disk.

Temperature and pressure at the center of the disk were extremely high. It was so hot that nuclear fusion reactions began. In these reactions, hydrogen atoms fuse, or join together, to form helium atoms. Extreme amounts of energy were released in these reactions. This is how the sun was born.

Other materials in the disk surrounding the Sun collided together. They formed the rest of the solar system. Small particles collided and became rocks. Rocks collided and became boulders. Eventually, the planets formed from the colliding material. Dwarf planets, comets, and asteroids formed as well.


  1. How did our solar system begin?
  2. Describe how the sun formed.
  3. Explain how other bodies of the solar system came about

Lesson 12.1: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. Our solar system began to form about
    1. 3 billion years ago.
    2. 4 billion years ago.
    3. 5 billion years ago.
    4. 10 billion years ago.
  2. When the solar nebula contracted and began to spin, it
    1. increased in temperature.
    2. increased in pressure.
    3. formed into a disk.
    4. all of the above
  3. The inner planets of our solar system include
    1. Pluto.
    2. Uranus.
    3. Saturn.
    4. Mercury.
  4. After the sun formed, material at similar distances from the sun collided to form each of the
    1. moons.
    2. planets.
    3. asteroids.
    4. comets.
  5. Earth formed about
    1. 4.5 billion years ago.
    2. 3 billion years ago.
    3. 1 billion years ago.
    4. 0.5 billion years ago.
  6. Gases in Earth’s early atmosphere included
    1. oxygen.
    2. water vapor.
    3. carbon dioxide.
    4. all of the above
  7. After the oceans formed on Earth’s surface, the
    1. water cycle began.
    2. atmosphere formed.
    3. mantle started to cool.
    4. all of the above

Lesson 12.1: Matching

Name___________________ Class______________ Date________

Match each definition with the correct term.


_____ 1. ring of icy debris just beyond Neptune

_____ 2. example of an object in the solar system

_____ 3. water in the gaseous state

_____ 4. gas missing from Earth’s early atmosphere

_____ 5. reaction in which hydrogen atoms change to helium

_____ 6. giant cloud of gas and dust from which the solar system formed

_____ 7. gases that surround a planet


a. atmosphere

b. nuclear fusion

c. comet

d. solar nebula

e. water vapor

f. Kuiper belt

g. oxygen

Lesson 12.1: Fill in the Blank

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

  1. Nuclear fusion reactions release huge amounts of __________.
  2. Scientists think that the moon formed when Earth was stuck by a(n) __________.
  3. Earth’s core is made mostly of the element __________.
  4. Earth’s __________ is made mostly of lightweight materials.
  5. In between Earth’s core and crust is the __________.
  6. Gases from Earth’s interior were released into the early atmosphere by __________.
  7. The oceans could form only after Earth’s atmosphere __________.

Lesson 12.1: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Explain how Earth’s atmosphere and oceans formed.

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