12.2 Early Earth
Lesson Objectives
- Describe how the Earth formed with other parts of the solar system more than 4 billion
years ago. - Explain how Earth’s atmosphere has changed over time.
- Explain the conditions that allowed the first forms of life to develop on Earth.
Introduction
Figure 12.3: The Earth from space. The Earth looks very different today than it did when
it first formed over 4 billion years ago. ( 22 )
Imagine that you had a movie that shows the history of Earth from its beginning to the
present day—as if a giant camera in space had recorded pictures of Earth over the last 4
1/2 billion years. How do you think the Earth would look in that movie at different times
in history? How do you think it has changed?
If you put the movie in fast-forward, you would see lots of action and lots of change! You
would see that our planet has undergone remarkable changes over billions of years (Figure