24.1  The Atmosphere (continued)

Earth's Protective Layer

What you commonly call air, scientists call the atmosphere. The atmosphere (at muh sfeer) is the layer of gases that surrounds Earth.   The atmosphere forms a protective boundary between Earth and space and provides conditions that are suitable for life. The atmosphere protects Earth's surface from continual pounding by meteoroids, chunks of rock and metal from space. The atmosphere also protects Earth from much of the high-energy radiation from space.

Figure 2  Dry air is a mixture of many gases. Air also contains water vapor, which makes up between 0.02 percent and 4.0 percent of air's volume.

The atmosphere holds in heat and helps to moderate Earth's temperatures. Without the atmosphere, Earth's surface would be similar to the moon's, boiling hot during the day and freezing cold at night. Earth's relatively constant temperatures allow life to flourish.

The atmosphere also provides the gases that are essential for life. Carbon dioxide in the atmosphere is essential for plants and some other organisms to carry out photosynthesis. Photosynthesis is the process of capturing the sun's energy to make food. Oxygen is produced during photosynthesis and released into the atmosphere. Your body uses oxygen to carry out many life functions.