chapter 2 notes

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The Earth is a rounded object that is slightly wider around the center than from top to bottom. Earth has a larger diameter at the Equator—about 7,930 miles (12,760 km)—than from Pole to Pole, but the difference is less than 1 percent. With a circumference of about 24,900 miles (40,060 km), Earth is the largest of the inner planets in the solar system.

The surface of the Earth is made up of water and land. About 70 percent of our planet’s surface is water. Oceans, lakes, rivers, underground water, and other bodies of water make up a part of the Earth called the hydrosphere.

About 30 percent of the Earth’s surface is land, including continents and islands. Land makes up a part of the Earth called the lithosphere, the Earth’s crust. The lithosphere also includes the ocean basins, or the land beneath the oceans.

The air we breathe is part of Earth’s atmosphere, a thin layer of gases extending above the planet’s surface. The atmosphere is composed of 78 percent nitrogen, 21 percent oxygen, and small amounts of argon and other gases.

All people, animals, and plants live on or close to the Earth’s surface or in the atmosphere. The part of the Earth that supports life is the biosphere. Life outside the biosphere, such as on a space station orbiting Earth, exists only with the assistance of mechanical life-support systems.

Landforms are natural features at the surface of the Earth’s lithosphere. Many of the Earth’s landforms have a particular shape or elevation. Landforms often contain rivers, lakes, and streams.