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Chapter 2: Earth as a Planet

Difficulty Level: Basic Created by: CK-12


Is Earth a planet?

Yes! No one doubts that Earth is a planet. But Earth is a lot different from the other planets in our solar system. The outer planets are huge and made of gas, like Jupiter. The inner planets are also different, like scorching-hot Venus. Earth is different because it has liquid water. It also has life! Life may be found on another planet or moon in our solar system. But it will not be intelligent life. We humans have looked around to know that! There was a planet that was really different from the other planets. That planet is no longer a planet. Pluto is now categorized as a dwarf planet. To decide what to do with Pluto, scientists had to decide what a planet is. We will look at some of the characteristics that make Earth a bona fide planet.

Chapter Outline

Chapter Summary


This Concept deals with some Earth basics. Earth is a planet and has the characteristics of a planet. Like other planets, it is nearly round. This is because it has enough mass for its gravity to pull material into a round shape. Earth's gravity has also pulled in small objects, like asteroids. So the planet's orbit is cleared. Earth rotates on its axis and revolves around its star. As a result of its rotation, Earth has a day-night cycle. The tilt of its axis creates the seasons. Earth has layers from crust to mantle to core. The core is divided into a liquid outer core and a solid inner core. The liquid outer core has convection, which generates the magnetic field. The mantle is solid rock. The crust has two major types: continental and oceanic. The crust and uppermost mantle make up the lithosphere. Beneath the lithosphere is the asthenosphere. The lithosphere is brittle and will break. The asthenosphere can flow.

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6 , 7

Date Created:

Jan 04, 2013

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Jan 02, 2015
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