Chapter 15

Earth’s Atmosphere

15.1 The Atmosphere

Lesson Objectives

• Describe the importance of the atmosphere to our planet and its life.


• Outline the role of the atmosphere in the water cycle.


• List the major components of the atmosphere and know their functions.


• Describe how atmospheric pressure changes with altitude.

Introduction

Earth’satmosphereisathinblanketofgasesandtinyparticles—togethercalledair. Without
air, the Earth would just be another lifeless rock orbiting the Sun. Although we are rarely
aware of it, air surrounds us. We are most aware of air when it moves, creating wind. Like
all gases, air takes up space. These gases that make up our air are packed closer together
near the Earth’s surface than at higher elevations.

All living things need some of the gases in air for life support. In particular, all organisms
rely on oxygen for respiration — even plants require oxygen to stay alive at night or when
the Sun is obscured. Plants also require carbon dioxide in the air for photosynthesis. All
weather happens in the atmosphere. The atmosphere has many other important roles as
well. These include moderating Earth’s temperatures and protecting living things from the
Sun’s most harmful rays.